/*****************************************************************************

Copyright (c) 1994, 2022, Oracle and/or its affiliates.
Copyright (c) 2012, Facebook Inc.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License, version 2.0, as published by the
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*****************************************************************************/

/** @file btr/btr0btr.cc
 The B-tree

 Created 6/2/1994 Heikki Tuuri
 *******************************************************/

#include "btr0btr.h"

#include <sys/types.h>

#ifndef UNIV_HOTBACKUP
#include "btr0cur.h"
#include "btr0pcur.h"
#include "btr0sea.h"
#include "buf0stats.h"
#include "dict0boot.h"
#include "fsp0sysspace.h"
#include "gis0geo.h"
#include "gis0rtree.h"
#include "ibuf0ibuf.h"
#include "lock0lock.h"
#include "my_dbug.h"
#include "page0page.h"
#include "page0zip.h"
#include "rem0cmp.h"
#include "srv0mon.h"
#include "trx0trx.h"
#include "ut0new.h"
#endif /* !UNIV_HOTBACKUP */

#ifndef UNIV_HOTBACKUP
/** Checks if the page in the cursor can be merged with given page.
 If necessary, re-organize the merge_page.
 @return        true if possible to merge. */
static bool btr_can_merge_with_page(
    btr_cur_t *cursor,         /*!< in: cursor on the page to merge */
    page_no_t page_no,         /*!< in: a sibling page */
    buf_block_t **merge_block, /*!< out: the merge block */
    mtr_t *mtr);               /*!< in: mini-transaction */
#endif                         /* !UNIV_HOTBACKUP */

/** Report that an index page is corrupted. */
void btr_corruption_report(const buf_block_t *block, /*!< in: corrupted block */
                           const dict_index_t *index) /*!< in: index tree */
{
  ib::error(ER_IB_MSG_27) << "Flag mismatch in page " << block->page.id
                          << " index " << index->name << " of table "
                          << index->table->name;
}

#ifndef UNIV_HOTBACKUP
/*
Latching strategy of the InnoDB B-tree
--------------------------------------
A tree latch protects all non-leaf nodes of the tree. Each node of a tree
also has a latch of its own.

A B-tree operation normally first acquires an S-latch on the tree. It
searches down the tree and releases the tree latch when it has the
leaf node latch. To save CPU time we do not acquire any latch on
non-leaf nodes of the tree during a search, those pages are only bufferfixed.

If an operation needs to restructure the tree, it acquires an X-latch on
the tree before searching to a leaf node. If it needs, for example, to
split a leaf,
(1) InnoDB decides the split point in the leaf,
(2) allocates a new page,
(3) inserts the appropriate node pointer to the first non-leaf level,
(4) releases the tree X-latch,
(5) and then moves records from the leaf to the new allocated page.

Node pointers
-------------
Leaf pages of a B-tree contain the index records stored in the
tree. On levels n > 0 we store 'node pointers' to pages on level
n - 1. For each page there is exactly one node pointer stored:
thus the our tree is an ordinary B-tree, not a B-link tree.

A node pointer contains a prefix P of an index record. The prefix
is long enough so that it determines an index record uniquely.
The file page number of the child page is added as the last
field. To the child page we can store node pointers or index records
which are >= P in the alphabetical order, but < P1 if there is
a next node pointer on the level, and P1 is its prefix.

If a node pointer with a prefix P points to a non-leaf child,
then the leftmost record in the child must have the same
prefix P. If it points to a leaf node, the child is not required
to contain any record with a prefix equal to P. The leaf case
is decided this way to allow arbitrary deletions in a leaf node
without touching upper levels of the tree.

We have predefined a special minimum record which we
define as the smallest record in any alphabetical order.
A minimum record is denoted by setting a bit in the record
header. A minimum record acts as the prefix of a node pointer
which points to a leftmost node on any level of the tree.

File page allocation
--------------------
In the root node of a B-tree there are two file segment headers.
The leaf pages of a tree are allocated from one file segment, to
make them consecutive on disk if possible. From the other file segment
we allocate pages for the non-leaf levels of the tree.
*/

#ifdef UNIV_BTR_DEBUG
/** Checks a file segment header within a B-tree root page.
 @return true if valid */
static bool btr_root_fseg_validate(
    const fseg_header_t *seg_header, /*!< in: segment header */
    space_id_t space)                /*!< in: tablespace identifier */
{
  ulint offset = mach_read_from_2(seg_header + FSEG_HDR_OFFSET);

  ut_a(mach_read_from_4(seg_header + FSEG_HDR_SPACE) == space);
  ut_a(offset >= FIL_PAGE_DATA);
  ut_a(offset <= UNIV_PAGE_SIZE - FIL_PAGE_DATA_END);
  return true;
}
#endif /* UNIV_BTR_DEBUG */

/** Gets the root node of a tree and x- or s-latches it.
 @return root page, x- or s-latched */
buf_block_t *btr_root_block_get(
    const dict_index_t *index, /*!< in: index tree */
    ulint mode,                /*!< in: either RW_S_LATCH
                               or RW_X_LATCH */
    mtr_t *mtr)                /*!< in: mtr */
{
  const space_id_t space_id = dict_index_get_space(index);
  const page_id_t page_id(space_id, dict_index_get_page(index));
  const page_size_t page_size(dict_table_page_size(index->table));

  buf_block_t *block =
      btr_block_get(page_id, page_size, mode, UT_LOCATION_HERE, index, mtr);

  btr_assert_not_corrupted(block, index);
#ifdef UNIV_BTR_DEBUG
  if (!dict_index_is_ibuf(index)) {
    const page_t *root = buf_block_get_frame(block);

    ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_LEAF + root,
                                space_id));
    ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_TOP + root,
                                space_id));
  }
#endif /* UNIV_BTR_DEBUG */

  return (block);
}

/** Gets the root node of a tree and sx-latches it for segment access.
 @return root page, sx-latched */
page_t *btr_root_get(const dict_index_t *index, /*!< in: index tree */
                     mtr_t *mtr)                /*!< in: mtr */
{
  /* Intended to be used for segment list access.
  SX lock doesn't block reading user data by other threads.
  And block the segment list access by others.*/
  return (buf_block_get_frame(btr_root_block_get(index, RW_SX_LATCH, mtr)));
}

/** Gets the height of the B-tree (the level of the root, when the leaf
 level is assumed to be 0). The caller must hold an S or X latch on
 the index.
 @return tree height (level of the root) */
ulint btr_height_get(dict_index_t *index, /*!< in: index tree */
                     mtr_t *mtr)          /*!< in/out: mini-transaction */
{
  ulint height;
  buf_block_t *root_block;

  ut_ad(srv_read_only_mode ||
        mtr_memo_contains_flagged(
            mtr, dict_index_get_lock(index),
            MTR_MEMO_S_LOCK | MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK) ||
        index->table->is_intrinsic());

  /* S latches the page */
  root_block = btr_root_block_get(index, RW_S_LATCH, mtr);

  height = btr_page_get_level(buf_block_get_frame(root_block));

  /* Release the S latch on the root page. */
  mtr->memo_release(root_block, MTR_MEMO_PAGE_S_FIX);

  ut_d(sync_check_unlock(&root_block->lock));

  return (height);
}

/** Checks a file segment header within a B-tree root page and updates
 the segment header space id.
 @return true if valid */
static bool btr_root_fseg_adjust_on_import(
    fseg_header_t *seg_header, /*!< in/out: segment header */
    page_zip_des_t *page_zip,  /*!< in/out: compressed page,
                               or NULL */
    space_id_t space,          /*!< in: tablespace identifier */
    mtr_t *mtr)                /*!< in/out: mini-transaction */
{
  page_no_t offset = mach_read_from_2(seg_header + FSEG_HDR_OFFSET);

  if (offset < FIL_PAGE_DATA || offset > UNIV_PAGE_SIZE - FIL_PAGE_DATA_END) {
    return false;

  } else if (page_zip) {
    mach_write_to_4(seg_header + FSEG_HDR_SPACE, space);
    page_zip_write_header(page_zip, seg_header + FSEG_HDR_SPACE, 4, mtr);
  } else {
    mlog_write_ulint(seg_header + FSEG_HDR_SPACE, space, MLOG_4BYTES, mtr);
  }

  return true;
}

/** Checks and adjusts the root node of a tree during IMPORT TABLESPACE.
 @return error code, or DB_SUCCESS */
dberr_t btr_root_adjust_on_import(
    const dict_index_t *index) /*!< in: index tree */
{
  dberr_t err;
  mtr_t mtr;
  page_t *page;
  buf_block_t *block;
  page_zip_des_t *page_zip;
  dict_table_t *table = index->table;
  const space_id_t space_id = dict_index_get_space(index);
  const page_id_t page_id(space_id, dict_index_get_page(index));
  const page_size_t page_size(dict_table_page_size(table));

  DBUG_EXECUTE_IF("ib_import_trigger_corruption_3", return (DB_CORRUPTION););

  mtr_start(&mtr);

  mtr_set_log_mode(&mtr, MTR_LOG_NO_REDO);

  block = btr_block_get(page_id, page_size, RW_X_LATCH, UT_LOCATION_HERE, index,
                        &mtr);

  page = buf_block_get_frame(block);
  page_zip = buf_block_get_page_zip(block);

  if (!page_is_root(page)) {
    err = DB_CORRUPTION;

  } else if (index->is_clustered()) {
    auto page_is_compact_format = page_is_comp(page);

    /* Check if the page format and table format agree. */
    if (page_is_compact_format != dict_table_is_comp(table)) {
      err = DB_CORRUPTION;
    } else {
      /* Check that the table flags and the tablespace
      flags match. */
      uint32_t flags = dict_tf_to_fsp_flags(table->flags);
      uint32_t fsp_flags = fil_space_get_flags(table->space);

      /* We remove SDI flag from space flags temporarily for
      comparison because the space flags derived from table
      flags will not have SDI flag */
      fsp_flags_unset_sdi(fsp_flags);

      /* As encryption is not a table property, we don't keep
      any encryption property related flag in table. Thus
      exclude encryption flag as well. */
      fsp_flags_unset_encryption(fsp_flags);

      err = fsp_flags_are_equal(flags, fsp_flags) ? DB_SUCCESS : DB_CORRUPTION;
    }
  } else {
    err = DB_SUCCESS;
  }

  /* Check and adjust the file segment headers, if all OK so far. */
  if (err == DB_SUCCESS &&
      (!btr_root_fseg_adjust_on_import(FIL_PAGE_DATA + PAGE_BTR_SEG_LEAF + page,
                                       page_zip, space_id, &mtr) ||
       !btr_root_fseg_adjust_on_import(FIL_PAGE_DATA + PAGE_BTR_SEG_TOP + page,
                                       page_zip, space_id, &mtr))) {
    err = DB_CORRUPTION;
  }

  mtr_commit(&mtr);

  return (err);
}

/** Creates a new index page (not the root, and also not
 used in page reorganization).  @see btr_page_empty(). */
void btr_page_create(
    buf_block_t *block,       /*!< in/out: page to be created */
    page_zip_des_t *page_zip, /*!< in/out: compressed page, or NULL */
    dict_index_t *index,      /*!< in: index */
    ulint level,              /*!< in: the B-tree level of the page */
    mtr_t *mtr)               /*!< in: mtr */
{
  page_t *page = buf_block_get_frame(block);

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));

  uint16_t page_create_type;
  if (dict_index_is_spatial(index)) {
    page_create_type = FIL_PAGE_RTREE;
  } else if (dict_index_is_sdi(index)) {
    page_create_type = FIL_PAGE_SDI;
  } else {
    page_create_type = FIL_PAGE_INDEX;
  }

  if (page_zip) {
    page_create_zip(block, index, level, 0, mtr, page_create_type);
  } else {
    page_create(block, mtr, dict_table_is_comp(index->table), page_create_type);
    /* Set the level of the new index page */
    btr_page_set_level(page, nullptr, level, mtr);
  }

  /* For Spatial Index, initialize the Split Sequence Number */
  if (dict_index_is_spatial(index)) {
    page_set_ssn_id(block, page_zip, 0, mtr);
  }

  btr_page_set_index_id(page, page_zip, index->id, mtr);

  if (level == 0) {
    buf_stat_per_index->inc(index_id_t(index->space, index->id));
  }
}

/** Allocates a new file page to be used in an ibuf tree. Takes the page from
 the free list of the tree, which must contain pages!
 @return new allocated block, x-latched */
static buf_block_t *btr_page_alloc_for_ibuf(
    dict_index_t *index, /*!< in: index tree */
    mtr_t *mtr)          /*!< in: mtr */
{
  fil_addr_t node_addr;
  page_t *root;
  page_t *new_page;
  buf_block_t *new_block;

  root = btr_root_get(index, mtr);

  node_addr = flst_get_first(root + PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST, mtr);
  ut_a(node_addr.page != FIL_NULL);

  new_block = buf_page_get(
      page_id_t(dict_index_get_space(index), node_addr.page),
      dict_table_page_size(index->table), RW_X_LATCH, UT_LOCATION_HERE, mtr);

  new_page = buf_block_get_frame(new_block);
  buf_block_dbg_add_level(new_block, SYNC_IBUF_TREE_NODE_NEW);

  flst_remove(root + PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST,
              new_page + PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST_NODE, mtr);
  ut_d(flst_validate(root + PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST, mtr));

  return (new_block);
}

/** Allocates a new file page to be used in an index tree. NOTE: we assume
 that the caller has made the reservation for free extents!
 @retval NULL if no page could be allocated
 @retval block, rw_lock_x_lock_count(&block->lock) == 1 if allocation succeeded
 (init_mtr == mtr, or the page was not previously freed in mtr),
 returned block is not allocated nor initialized otherwise */
[[nodiscard]] static buf_block_t *btr_page_alloc_low(
    dict_index_t *index,    /*!< in: index */
    page_no_t hint_page_no, /*!< in: hint of a good page */
    byte file_direction,    /*!< in: direction where a possible
                            page split is made */
    ulint level,            /*!< in: level where the page is placed
                            in the tree */
    mtr_t *mtr,             /*!< in/out: mini-transaction
                            for the allocation */
    mtr_t *init_mtr)        /*!< in/out: mtr or another
                            mini-transaction in which the
                            page should be initialized.
                            If init_mtr!=mtr, but the page
                            is already X-latched in mtr, do
                            not initialize the page. */
{
  fseg_header_t *seg_header;
  page_t *root;

  root = btr_root_get(index, mtr);

  if (level == 0) {
    seg_header = root + PAGE_HEADER + PAGE_BTR_SEG_LEAF;
  } else {
    seg_header = root + PAGE_HEADER + PAGE_BTR_SEG_TOP;
  }

  /* Parameter true below states that the caller has made the
  reservation for free extents, and thus we know that a page can
  be allocated. However, for the cases where the file size is
  either smaller than an extent or same as the initial size,
  the fsp_reserve_free_extents returns reserved extents as 0.
  This can be true even if the initial allocation is about
  to be completely filled up. The function below is a point
  of no return and expects that enough space is already allocated.
  However, the callers of this function rely on the success/failure
  return by fsp_reserve_free_extents, which does not really guarantee
  that a whole extent has been reserved.
  The function fseg_alloc_free_page_general should attempt to ensure
  enough space is reserved before proceeding ahead. */
  uint64_t reserved_ext = fil_space_get_n_reserved_extents(
      page_get_space_id(page_align(seg_header)));

  return (fseg_alloc_free_page_general(seg_header, hint_page_no, file_direction,
                                       reserved_ext > 0, mtr, init_mtr));
}

buf_block_t *btr_page_alloc_priv(
    dict_index_t *index, page_no_t hint_page_no, byte file_direction,
    ulint level, mtr_t *mtr,
    mtr_t *init_mtr IF_DEBUG(, const ut::Location &loc [[maybe_unused]])) {
  buf_block_t *new_block;

  if (dict_index_is_ibuf(index)) {
    return (btr_page_alloc_for_ibuf(index, mtr));
  }

  new_block = btr_page_alloc_low(index, hint_page_no, file_direction, level,
                                 mtr, init_mtr);

  if (new_block) {
    buf_block_dbg_add_level(new_block, SYNC_TREE_NODE_NEW);
  }

  return (new_block);
}

/** Gets the number of pages in a B-tree.
 @return number of pages, or ULINT_UNDEFINED if the index is unavailable */
ulint btr_get_size(dict_index_t *index, /*!< in: index */
                   ulint flag, /*!< in: BTR_N_LEAF_PAGES or BTR_TOTAL_SIZE */
                   mtr_t *mtr) /*!< in/out: mini-transaction where index
                               is s-latched */
{
  fseg_header_t *seg_header;
  page_t *root;
  ulint n;
  ulint dummy;

  ut_ad(srv_read_only_mode ||
        mtr_memo_contains(mtr, dict_index_get_lock(index), MTR_MEMO_S_LOCK) ||
        index->table->is_intrinsic());
  ut_ad(index->page >= FSP_FIRST_INODE_PAGE_NO);

  if (index->page == FIL_NULL || dict_index_is_online_ddl(index) ||
      !index->is_committed()) {
    return (ULINT_UNDEFINED);
  }

  root = btr_root_get(index, mtr);

  if (flag == BTR_N_LEAF_PAGES) {
    seg_header = root + PAGE_HEADER + PAGE_BTR_SEG_LEAF;

    fseg_n_reserved_pages(seg_header, &n, mtr);

  } else if (flag == BTR_TOTAL_SIZE) {
    seg_header = root + PAGE_HEADER + PAGE_BTR_SEG_TOP;

    n = fseg_n_reserved_pages(seg_header, &dummy, mtr);

    seg_header = root + PAGE_HEADER + PAGE_BTR_SEG_LEAF;

    n += fseg_n_reserved_pages(seg_header, &dummy, mtr);
  } else {
    ut_error;
  }

  return (n);
}

/** Frees a page used in an ibuf tree. Puts the page to the free list of the
 ibuf tree. */
static void btr_page_free_for_ibuf(
    dict_index_t *index, /*!< in: index tree */
    buf_block_t *block,  /*!< in: block to be freed, x-latched */
    mtr_t *mtr)          /*!< in: mtr */
{
  page_t *root;

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));
  root = btr_root_get(index, mtr);

  flst_add_first(
      root + PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST,
      buf_block_get_frame(block) + PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST_NODE,
      mtr);

  ut_d(flst_validate(root + PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST, mtr));
}

void btr_page_free_low(dict_index_t *index, buf_block_t *block, ulint level,
                       mtr_t *mtr) {
  fseg_header_t *seg_header;
  page_t *root;

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));
  /* The page gets invalid for optimistic searches: increment the frame
  modify clock */

  buf_block_modify_clock_inc(block);

  if (dict_index_is_ibuf(index)) {
    btr_page_free_for_ibuf(index, block, mtr);

    return;
  }

  root = btr_root_get(index, mtr);

  if (level == 0 || level == ULINT_UNDEFINED) {
    seg_header = root + PAGE_HEADER + PAGE_BTR_SEG_LEAF;
  } else {
    seg_header = root + PAGE_HEADER + PAGE_BTR_SEG_TOP;
  }

#ifdef UNIV_GIS_DEBUG
  if (dict_index_is_spatial(index)) {
    fprintf(stderr, "GIS_DIAG: Freed  %ld\n", (long)block->page.id.page_no());
  }
#endif

  fseg_free_page(seg_header, block->page.id.space(), block->page.id.page_no(),
                 level != ULINT_UNDEFINED, mtr);

  /* The page was marked free in the allocation bitmap, but it
  should remain buffer-fixed until mtr_commit(mtr) or until it
  is explicitly freed from the mini-transaction. */
  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));
  /* TODO: Discard any operations on the page from the redo log
  and remove the block from the flush list and the buffer pool.
  This would free up buffer pool earlier and reduce writes to
  both the tablespace and the redo log. */
}

/** Frees a file page used in an index tree. NOTE: cannot free field external
 storage pages because the page must contain info on its level. */
void btr_page_free(dict_index_t *index, /*!< in: index tree */
                   buf_block_t *block,  /*!< in: block to be freed, x-latched */
                   mtr_t *mtr)          /*!< in: mtr */
{
  const page_t *page = buf_block_get_frame(block);
  ulint level = btr_page_get_level(page);

  ut_ad(fil_page_index_page_check(block->frame));
  ut_ad(level != ULINT_UNDEFINED);
  btr_page_free_low(index, block, level, mtr);
}

/** Sets the child node file address in a node pointer. */
static inline void btr_node_ptr_set_child_page_no(
    rec_t *rec,               /*!< in: node pointer record */
    page_zip_des_t *page_zip, /*!< in/out: compressed page whose uncompressed
                             part will be updated, or NULL */
    const ulint *offsets,     /*!< in: array returned by rec_get_offsets() */
    page_no_t page_no,        /*!< in: child node address */
    mtr_t *mtr)               /*!< in: mtr */
{
  byte *field;
  ulint len;

  ut_ad(rec_offs_validate(rec, nullptr, offsets));
  ut_ad(!page_is_leaf(page_align(rec)));
  ut_ad(!rec_offs_comp(offsets) || rec_get_node_ptr_flag(rec));

  /* The child address is in the last field */
  field = const_cast<byte *>(rec_get_nth_field(
      nullptr, rec, offsets, rec_offs_n_fields(offsets) - 1, &len));

  ut_ad(len == REC_NODE_PTR_SIZE);

  if (page_zip) {
    page_zip_write_node_ptr(page_zip, rec, rec_offs_data_size(offsets), page_no,
                            mtr);
  } else {
    mlog_write_ulint(field, page_no, MLOG_4BYTES, mtr);
  }
}

buf_block_t *btr_node_ptr_get_child(const rec_t *node_ptr, dict_index_t *index,
                                    const ulint *offsets, mtr_t *mtr,
                                    rw_lock_type_t type) {
  ut_ad(rec_offs_validate(node_ptr, index, offsets));

  const page_id_t page_id(page_get_space_id(page_align(node_ptr)),
                          btr_node_ptr_get_child_page_no(node_ptr, offsets));

  return (btr_block_get(page_id, dict_table_page_size(index->table), type,
                        UT_LOCATION_HERE, index, mtr));
}

/** Returns the upper level node pointer to a page. It is assumed that mtr holds
 an sx-latch on the tree.
 @param[in] offsets work area for the return value
 @param[in] heap memory heap to use
 @param[in,out] cursor in: cursor pointing to user record, out: cursor on node
 pointer record, its page x-latched
 @param[in] latch_mode BTR_CONT_MODIFY_TREE or BTR_CONT_SEARCH_TREE
 @param[in] location location where called
 @param[in] mtr mtr
 @return rec_get_offsets() of the node pointer record */
static ulint *btr_page_get_father_node_ptr_func(
    ulint *offsets, mem_heap_t *heap, btr_cur_t *cursor, ulint latch_mode,
    ut::Location location, mtr_t *mtr) {
  dtuple_t *tuple;
  rec_t *user_rec;
  rec_t *node_ptr;
  ulint level;
  page_no_t page_no;
  dict_index_t *index;

  ut_ad(latch_mode == BTR_CONT_MODIFY_TREE ||
        latch_mode == BTR_CONT_SEARCH_TREE);

  page_no = btr_cur_get_block(cursor)->page.id.page_no();
  index = cursor->index;
  ut_ad(!dict_index_is_spatial(index));

  ut_ad(srv_read_only_mode ||
        mtr_memo_contains_flagged(mtr, dict_index_get_lock(index),
                                  MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK) ||
        index->table->is_intrinsic());

  ut_ad(dict_index_get_page(index) != page_no);

  level = btr_page_get_level(btr_cur_get_page(cursor));

  user_rec = btr_cur_get_rec(cursor);
  ut_a(page_rec_is_user_rec(user_rec));

  tuple = dict_index_build_node_ptr(index, user_rec, 0, heap, level);
  if (index->table->is_intrinsic()) {
    btr_cur_search_to_nth_level_with_no_latch(
        index, level + 1, tuple, PAGE_CUR_LE, cursor, location.filename,
        location.line, mtr);
  } else {
    btr_cur_search_to_nth_level(index, level + 1, tuple, PAGE_CUR_LE,
                                latch_mode, cursor, 0, location.filename,
                                location.line, mtr);
  }

  node_ptr = btr_cur_get_rec(cursor);
  ut_ad(!page_rec_is_comp(node_ptr) ||
        rec_get_status(node_ptr) == REC_STATUS_NODE_PTR);
  offsets = rec_get_offsets(node_ptr, index, offsets, ULINT_UNDEFINED, &heap);

  if (btr_node_ptr_get_child_page_no(node_ptr, offsets) != page_no) {
    rec_t *print_rec;

    ib::error(ER_IB_MSG_28)
        << "Corruption of an index tree: table " << index->table->name
        << " index " << index->name << ", father ptr page no "
        << btr_node_ptr_get_child_page_no(node_ptr, offsets)
        << ", child page no " << page_no;

    print_rec = page_rec_get_next(page_get_infimum_rec(page_align(user_rec)));
    offsets =
        rec_get_offsets(print_rec, index, offsets, ULINT_UNDEFINED, &heap);
    page_rec_print(print_rec, offsets);
    offsets = rec_get_offsets(node_ptr, index, offsets, ULINT_UNDEFINED, &heap);
    page_rec_print(node_ptr, offsets);

    ib::fatal(UT_LOCATION_HERE, ER_IB_MSG_29)
        << "You should dump + drop + reimport the table to"
        << " fix the corruption. If the crash happens at"
        << " database startup. " << FORCE_RECOVERY_MSG
        << " Then dump + drop + reimport.";
  }

  return (offsets);
}

inline ulint *btr_page_get_father_node_ptr(ulint *offsets, mem_heap_t *heap,
                                           btr_cur_t *cursor,
                                           ut::Location location, mtr_t *mtr) {
  return btr_page_get_father_node_ptr_func(offsets, heap, cursor,
                                           BTR_CONT_MODIFY_TREE, location, mtr);
}

inline ulint *btr_page_get_father_node_ptr_for_validate(ulint *offsets,
                                                        mem_heap_t *heap,
                                                        btr_cur_t *cursor,
                                                        ut::Location location,
                                                        mtr_t *mtr) {
  return btr_page_get_father_node_ptr_func(offsets, heap, cursor,
                                           BTR_CONT_SEARCH_TREE, location, mtr);
}

/** Returns the upper level node pointer to a page. It is assumed that mtr holds
 an x-latch on the tree.
 @return rec_get_offsets() of the node pointer record */
static ulint *btr_page_get_father_block(
    ulint *offsets,      /*!< in: work area for the return value */
    mem_heap_t *heap,    /*!< in: memory heap to use */
    dict_index_t *index, /*!< in: b-tree index */
    buf_block_t *block,  /*!< in: child page in the index */
    mtr_t *mtr,          /*!< in: mtr */
    btr_cur_t *cursor)   /*!< out: cursor on node pointer record,
                         its page x-latched */
{
  rec_t *rec =
      page_rec_get_next(page_get_infimum_rec(buf_block_get_frame(block)));
  btr_cur_position(index, rec, block, cursor);
  return btr_page_get_father_node_ptr(offsets, heap, cursor, UT_LOCATION_HERE,
                                      mtr);
}

/** Seeks to the upper level node pointer to a page.
 It is assumed that mtr holds an x-latch on the tree. */
static void btr_page_get_father(
    dict_index_t *index, /*!< in: b-tree index */
    buf_block_t *block,  /*!< in: child page in the index */
    mtr_t *mtr,          /*!< in: mtr */
    btr_cur_t *cursor)   /*!< out: cursor on node pointer record,
                         its page x-latched */
{
  mem_heap_t *heap;
  rec_t *rec =
      page_rec_get_next(page_get_infimum_rec(buf_block_get_frame(block)));
  btr_cur_position(index, rec, block, cursor);

  heap = mem_heap_create(100, UT_LOCATION_HERE);
  btr_page_get_father_node_ptr(nullptr, heap, cursor, UT_LOCATION_HERE, mtr);
  mem_heap_free(heap);
}

/** Free a B-tree root page. btr_free_but_not_root() must already
have been called.
In a persistent tablespace, the caller must invoke fsp_init_file_page()
before mtr.commit().
@param[in,out]  block   Index root page
@param[in,out]  mtr     Mini-transaction */
static void btr_free_root(buf_block_t *block, mtr_t *mtr) {
  fseg_header_t *header;

  ut_ad(mtr_memo_contains_flagged(mtr, block, MTR_MEMO_PAGE_X_FIX));

  btr_search_drop_page_hash_index(block);

  header = buf_block_get_frame(block) + PAGE_HEADER + PAGE_BTR_SEG_TOP;
#ifdef UNIV_BTR_DEBUG
  ut_a(btr_root_fseg_validate(header, block->page.id.space()));
#endif /* UNIV_BTR_DEBUG */

  while (!fseg_free_step(header, true, mtr)) {
    /* Free the entire segment in small steps. */
  }
}

/** PAGE_INDEX_ID value for freed index B-trees */
static const space_index_t BTR_FREED_INDEX_ID = 0;

/** Invalidate an index root page so that btr_free_root_check()
will not find it.
@param[in,out]  block   Index root page
@param[in,out]  mtr     Mini-transaction */
static void btr_free_root_invalidate(buf_block_t *block, mtr_t *mtr) {
  ut_ad(page_is_root(block->frame));

  btr_page_set_index_id(buf_block_get_frame(block),
                        buf_block_get_page_zip(block), BTR_FREED_INDEX_ID, mtr);
}

/** Prepare to free a B-tree.
@param[in]      page_id         Page id
@param[in]      page_size Page size
@param[in]      index_id        PAGE_INDEX_ID contents
@param[in,out]  mtr             Mini-transaction
@return root block, to invoke btr_free_but_not_root() and btr_free_root()
@retval NULL if the page is no longer a matching B-tree page */
[[nodiscard]] static buf_block_t *btr_free_root_check(
    const page_id_t &page_id, const page_size_t &page_size,
    space_index_t index_id, mtr_t *mtr) {
  ut_ad(!fsp_is_system_temporary(page_id.space()));
  ut_ad(index_id != BTR_FREED_INDEX_ID);

  buf_block_t *block =
      buf_page_get(page_id, page_size, RW_X_LATCH, UT_LOCATION_HERE, mtr);
  buf_block_dbg_add_level(block, SYNC_TREE_NODE);

  if (fil_page_index_page_check(block->frame) &&
      index_id == btr_page_get_index_id(block->frame)) {
    /* This should be a root page.
    It should not be possible to reassign the same
    index_id for some other index in the tablespace. */
    ut_ad(page_is_root(block->frame));
  } else {
    block = nullptr;
  }

  return (block);
}

ulint btr_create(ulint type, space_id_t space, space_index_t index_id,
                 dict_index_t *index, mtr_t *mtr) {
  page_no_t page_no;
  buf_block_t *block;
  buf_frame_t *frame;
  page_t *page;
  page_zip_des_t *page_zip;

  ut_ad(index_id != BTR_FREED_INDEX_ID);

  /* Create the two new segments (one, in the case of an ibuf tree) for
  the index tree; the segment headers are put on the allocated root page
  (for an ibuf tree, not in the root, but on a separate ibuf header
  page) */

  if (type & DICT_IBUF) {
    /* Allocate first the ibuf header page */
    buf_block_t *ibuf_hdr_block =
        fseg_create(space, 0, IBUF_HEADER + IBUF_TREE_SEG_HEADER, mtr);

    if (ibuf_hdr_block == nullptr) {
      return (FIL_NULL);
    }

    buf_block_dbg_add_level(ibuf_hdr_block, SYNC_IBUF_TREE_NODE_NEW);

    ut_ad(ibuf_hdr_block->page.id.page_no() == IBUF_HEADER_PAGE_NO);
    /* Allocate then the next page to the segment: it will be the
    tree root page */

    block = fseg_alloc_free_page(buf_block_get_frame(ibuf_hdr_block) +
                                     IBUF_HEADER + IBUF_TREE_SEG_HEADER,
                                 IBUF_TREE_ROOT_PAGE_NO, FSP_UP, mtr);
    ut_ad(block->page.id.page_no() == IBUF_TREE_ROOT_PAGE_NO);
  } else {
    block = fseg_create(space, 0, PAGE_HEADER + PAGE_BTR_SEG_TOP, mtr);
  }

  if (block == nullptr) {
    return (FIL_NULL);
  }

  page_no = block->page.id.page_no();
  frame = buf_block_get_frame(block);

  if (type & DICT_IBUF) {
    /* It is an insert buffer tree: initialize the free list */
    buf_block_dbg_add_level(block, SYNC_IBUF_TREE_NODE_NEW);

    ut_ad(page_no == IBUF_TREE_ROOT_PAGE_NO);

    flst_init(frame + PAGE_HEADER + PAGE_BTR_IBUF_FREE_LIST, mtr);
  } else {
    /* It is a non-ibuf tree: create a file segment for leaf
    pages */
    buf_block_dbg_add_level(block, SYNC_TREE_NODE_NEW);

    if (!fseg_create(space, page_no, PAGE_HEADER + PAGE_BTR_SEG_LEAF, mtr)) {
      /* Not enough space for new segment, free root
      segment before return. */
      btr_free_root(block, mtr);
      if (!index->table->is_temporary()) {
        btr_free_root_invalidate(block, mtr);
      }

      return (FIL_NULL);
    }

    /* The fseg create acquires a second latch on the page,
    therefore we must declare it: */
    buf_block_dbg_add_level(block, SYNC_TREE_NODE_NEW);
  }

  uint16_t page_create_type;
  if (dict_index_is_spatial(index)) {
    page_create_type = FIL_PAGE_RTREE;
  } else if (dict_index_is_sdi(index)) {
    page_create_type = FIL_PAGE_SDI;
  } else {
    page_create_type = FIL_PAGE_INDEX;
  }

  /* Create a new index page on the allocated segment page */
  page_zip = buf_block_get_page_zip(block);

  if (page_zip) {
    page = page_create_zip(block, index, 0, 0, mtr, page_create_type);
  } else {
    page = page_create(block, mtr, dict_table_is_comp(index->table),
                       page_create_type);
    /* Set the level of the new index page */
    btr_page_set_level(page, nullptr, 0, mtr);
  }

  /* Set the index id of the page */
  btr_page_set_index_id(page, page_zip, index_id, mtr);

  /* Set the next node and previous node fields */
  btr_page_set_next(page, page_zip, FIL_NULL, mtr);
  btr_page_set_prev(page, page_zip, FIL_NULL, mtr);

  /* We reset the free bits for the page to allow creation of several
  trees in the same mtr, otherwise the latch on a bitmap page would
  prevent it because of the latching order.

  Note: Insert Buffering is disabled for temporary tables given that
  most temporary tables are smaller in size and short-lived. */
  if (!(type & DICT_CLUSTERED) && !index->table->is_temporary()) {
    ibuf_reset_free_bits(block);
  }

  /* In the following assertion we test that two records of maximum
  allowed size fit on the root page: this fact is needed to ensure
  correctness of split algorithms */

  ut_ad(page_get_max_insert_size(page, 2) > 2 * BTR_PAGE_MAX_REC_SIZE);

  buf_stat_per_index->inc(index_id_t(space, index_id));

  return (page_no);
}

/** Free a B-tree except the root page. The root page MUST be freed after
this by calling btr_free_root.
@param[in,out]  block           root page
@param[in]      log_mode        mtr logging mode */
static void btr_free_but_not_root(buf_block_t *block, mtr_log_t log_mode) {
  bool finished;
  mtr_t mtr;

  ut_ad(page_is_root(block->frame));
leaf_loop:
  mtr_start(&mtr);
  mtr_set_log_mode(&mtr, log_mode);

  page_t *root = block->frame;

#ifdef UNIV_BTR_DEBUG
  ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_LEAF + root,
                              block->page.id.space()));
  ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_TOP + root,
                              block->page.id.space()));
#endif /* UNIV_BTR_DEBUG */

  /* NOTE: page hash indexes are dropped when a page is freed inside
  fsp0fsp. */

  finished = fseg_free_step(root + PAGE_HEADER + PAGE_BTR_SEG_LEAF, true, &mtr);
  mtr_commit(&mtr);

  if (!finished) {
    goto leaf_loop;
  }
top_loop:
  mtr_start(&mtr);
  mtr_set_log_mode(&mtr, log_mode);

  root = block->frame;

#ifdef UNIV_BTR_DEBUG
  ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_TOP + root,
                              block->page.id.space()));
#endif /* UNIV_BTR_DEBUG */

  finished = fseg_free_step_not_header(root + PAGE_HEADER + PAGE_BTR_SEG_TOP,
                                       true, &mtr);
  mtr_commit(&mtr);

  if (!finished) {
    goto top_loop;
  }
}

/** Free a persistent index tree if it exists.
@param[in]      page_id         Root page id
@param[in]      page_size       Page size
@param[in]      index_id        PAGE_INDEX_ID contents
@param[in,out]  mtr             Mini-transaction */
void btr_free_if_exists(const page_id_t &page_id, const page_size_t &page_size,
                        space_index_t index_id, mtr_t *mtr) {
  buf_block_t *root = btr_free_root_check(page_id, page_size, index_id, mtr);

  if (root == nullptr) {
    return;
  }

  btr_free_but_not_root(root, mtr->get_log_mode());
  btr_free_root(root, mtr);
  btr_free_root_invalidate(root, mtr);
}

/** Free an index tree in a temporary tablespace.
@param[in]      page_id         root page id
@param[in]      page_size       page size */
void btr_free(const page_id_t &page_id, const page_size_t &page_size) {
  mtr_t mtr;
  mtr.start();
  mtr.set_log_mode(MTR_LOG_NO_REDO);

  buf_block_t *block =
      buf_page_get(page_id, page_size, RW_X_LATCH, UT_LOCATION_HERE, &mtr);

  ut_ad(page_is_root(block->frame));

  btr_free_but_not_root(block, MTR_LOG_NO_REDO);
  btr_free_root(block, &mtr);
  mtr.commit();
}

/** Truncate an index tree. We just free all except the root.
Currently, this function is only specific for clustered indexes and the only
caller is DDTableBuffer which manages a table with only a clustered index.
It is up to the caller to ensure atomicity and to ensure correct recovery by
calling btr_truncate_recover().
@param[in]      index           clustered index */
void btr_truncate(const dict_index_t *index) {
  ut_ad(index->is_clustered());
  ut_ad(index->next() == nullptr);

  page_no_t root_page_no = index->page;
  space_id_t space_id = index->space;
  fil_space_t *space = fil_space_acquire_silent(space_id);

  if (space == nullptr) {
    return;
  }

  page_size_t page_size(space->flags);
  const page_id_t page_id(space_id, root_page_no);
  mtr_t mtr;
  buf_block_t *block;

  mtr.start();

  mtr_x_lock(&space->latch, &mtr, UT_LOCATION_HERE);

  block = buf_page_get(page_id, page_size, RW_X_LATCH, UT_LOCATION_HERE, &mtr);

  page_t *page = buf_block_get_frame(block);
  ut_ad(page_is_root(page));

  /* Mark that we are going to truncate the index tree
  We use PAGE_MAX_TRX_ID as it should be always 0 for clustered
  index. */
  mlog_write_ull(page + (PAGE_HEADER + PAGE_MAX_TRX_ID), IB_ID_MAX, &mtr);

  mtr.commit();

  mtr.start();

  block = buf_page_get(page_id, page_size, RW_X_LATCH, UT_LOCATION_HERE, &mtr);

  /* Free all except the root, we don't want to change it. */
  btr_free_but_not_root(block, MTR_LOG_ALL);

  /* Reset the mark saying that we have finished the truncate.
  The PAGE_MAX_TRX_ID would be reset here. */
  page_create(block, &mtr, dict_table_is_comp(index->table), false);
  ut_ad(buf_block_get_frame(block) + (PAGE_HEADER + PAGE_MAX_TRX_ID) ==
        nullptr);

  mtr.commit();

  rw_lock_x_unlock(&space->latch);

  fil_space_release(space);
}

/** Recovery function for btr_truncate. We will check if there is a
crash during btr_truncate, if so, do recover it, if not, do nothing.
@param[in]      index           clustered index */
void btr_truncate_recover(const dict_index_t *index) {
  ut_ad(index->is_clustered());
  ut_ad(index->next() == nullptr);

  page_no_t root_page_no = index->page;
  space_id_t space_id = index->space;
  fil_space_t *space = fil_space_acquire_silent(space_id);

  if (space == nullptr) {
    return;
  }

  page_size_t page_size(space->flags);
  const page_id_t page_id(space_id, root_page_no);
  mtr_t mtr;
  buf_block_t *block;

  mtr.start();

  block = buf_page_get(page_id, page_size, RW_X_LATCH, UT_LOCATION_HERE, &mtr);

  page_t *page = buf_block_get_frame(block);

  trx_id_t trx_id = page_get_max_trx_id(page);
  ut_ad(trx_id == 0 || trx_id == IB_ID_MAX);

  mtr.commit();

  fil_space_release(space);

  if (trx_id == IB_ID_MAX) {
    /* -1 means there is a half-done btr_truncate,
    we can simple redo it again. */
    btr_truncate(index);
  }
}
#endif /* !UNIV_HOTBACKUP */

bool btr_page_reorganize_low(bool recovery, ulint z_level, page_cur_t *cursor,
                             dict_index_t *index, mtr_t *mtr) {
  buf_block_t *block = page_cur_get_block(cursor);
#ifndef UNIV_HOTBACKUP
  buf_pool_t *buf_pool = buf_pool_from_bpage(&block->page);
#endif /* !UNIV_HOTBACKUP */
  page_t *page = buf_block_get_frame(block);
  page_zip_des_t *page_zip = buf_block_get_page_zip(block);
  buf_block_t *temp_block;
  page_t *temp_page;
  ulint data_size1;
  ulint data_size2;
  ulint max_ins_size1;
  ulint max_ins_size2;
  bool success = false;
  ulint pos;
  bool log_compressed;

#ifndef UNIV_HOTBACKUP
  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));
#endif /* !UNIV_HOTBACKUP */
  btr_assert_not_corrupted(block, index);
#ifdef UNIV_ZIP_DEBUG
  ut_a(!page_zip || page_zip_validate(page_zip, page, index));
#endif /* UNIV_ZIP_DEBUG */
  data_size1 = page_get_data_size(page);
  max_ins_size1 = page_get_max_insert_size_after_reorganize(page, 1);

  /* Turn logging off */
  mtr_log_t log_mode = mtr_set_log_mode(mtr, MTR_LOG_NONE);

#ifndef UNIV_HOTBACKUP
  temp_block = buf_block_alloc(buf_pool);
#else  /* !UNIV_HOTBACKUP */
  temp_block = back_block2;
#endif /* !UNIV_HOTBACKUP */
  temp_page = temp_block->frame;

#ifndef UNIV_HOTBACKUP
  MONITOR_INC(MONITOR_INDEX_REORG_ATTEMPTS);
#endif /* !UNIV_HOTBACKUP */

  /* Copy the old page to temporary space */
  buf_frame_copy(temp_page, page);

#ifndef UNIV_HOTBACKUP
  if (!recovery) {
    btr_search_drop_page_hash_index(block);
  }
#endif /* !UNIV_HOTBACKUP */

  /* Save the cursor position. */
  pos = page_rec_get_n_recs_before(page_cur_get_rec(cursor));

  /* Recreate the page: note that global data on page (possible
  segment headers, next page-field, etc.) is preserved intact */

  page_create(block, mtr, dict_table_is_comp(index->table),
              fil_page_get_type(page));

  /* Copy the records from the temporary space to the recreated page;
  do not copy the lock bits yet */

  page_copy_rec_list_end_no_locks(block, temp_block,
                                  page_get_infimum_rec(temp_page), index, mtr);

  /* Multiple transactions cannot simultaneously operate on the
  same temp-table in parallel.
  max_trx_id is ignored for temp tables because it not required
  for MVCC. */
  if (dict_index_is_sec_or_ibuf(index) && page_is_leaf(page) &&
      !index->table->is_temporary()) {
    /* Copy max trx id to recreated page */
    trx_id_t max_trx_id = page_get_max_trx_id(temp_page);
    page_set_max_trx_id(block, nullptr, max_trx_id, mtr);
    /* In crash recovery, dict_index_is_sec_or_ibuf() always
    holds, even for clustered indexes.  max_trx_id is
    unused in clustered index pages. */
    ut_ad(max_trx_id != 0 || recovery);
  }

  /* If innodb_log_compressed_pages is ON, page reorganize should log the
  compressed page image.*/
  log_compressed = page_zip && page_zip_log_pages;

  if (log_compressed) {
    mtr_set_log_mode(mtr, log_mode);
  }

  if (page_zip && !page_zip_compress(page_zip, page, index, z_level, mtr)) {
    /* Restore the old page and exit. */
#if defined UNIV_DEBUG || defined UNIV_ZIP_DEBUG
    /* Check that the bytes that we skip are identical. */
    ut_a(!memcmp(page, temp_page, PAGE_HEADER));
    ut_a(!memcmp(PAGE_HEADER + PAGE_N_RECS + page,
                 PAGE_HEADER + PAGE_N_RECS + temp_page,
                 PAGE_DATA - (PAGE_HEADER + PAGE_N_RECS)));
    ut_a(!memcmp(UNIV_PAGE_SIZE - FIL_PAGE_DATA_END + page,
                 UNIV_PAGE_SIZE - FIL_PAGE_DATA_END + temp_page,
                 FIL_PAGE_DATA_END));
#endif /* UNIV_DEBUG || UNIV_ZIP_DEBUG */

    memcpy(PAGE_HEADER + page, PAGE_HEADER + temp_page,
           PAGE_N_RECS - PAGE_N_DIR_SLOTS);
    memcpy(PAGE_DATA + page, PAGE_DATA + temp_page,
           UNIV_PAGE_SIZE - PAGE_DATA - FIL_PAGE_DATA_END);

#if defined UNIV_DEBUG || defined UNIV_ZIP_DEBUG
    ut_a(!memcmp(page, temp_page, UNIV_PAGE_SIZE));
#endif /* UNIV_DEBUG || UNIV_ZIP_DEBUG */

    goto func_exit;
  }

#ifndef UNIV_HOTBACKUP
  /* No locks are acquried for intrinsic tables. */
  if (!recovery && !dict_table_is_locking_disabled(index->table)) {
    /* Update the record lock bitmaps */
    lock_move_reorganize_page(block, temp_block);
  }
#endif /* !UNIV_HOTBACKUP */

  data_size2 = page_get_data_size(page);
  max_ins_size2 = page_get_max_insert_size_after_reorganize(page, 1);

  if (data_size1 != data_size2 || max_ins_size1 != max_ins_size2) {
    ib::error(ER_IB_MSG_30)
        << "Page old data size " << data_size1 << " new data size "
        << data_size2 << ", page old max ins size " << max_ins_size1
        << " new max ins size " << max_ins_size2;

    ib::error(ER_IB_MSG_31) << BUG_REPORT_MSG;
    ut_d(ut_error);
  } else {
    success = true;
  }

  /* Restore the cursor position. */
  if (pos > 0) {
    cursor->rec = page_rec_get_nth(page, pos);
  } else {
    ut_ad(cursor->rec == page_get_infimum_rec(page));
  }

func_exit:
#ifdef UNIV_ZIP_DEBUG
  ut_a(!page_zip || page_zip_validate(page_zip, page, index));
#endif /* UNIV_ZIP_DEBUG */
#ifndef UNIV_HOTBACKUP
  buf_block_free(temp_block);
#endif /* !UNIV_HOTBACKUP */

  /* Restore logging mode */
  mtr_set_log_mode(mtr, log_mode);

#ifndef UNIV_HOTBACKUP
  if (success) {
    mlog_id_t type;
    byte *log_ptr = nullptr;

    /* Write the log record */
    if (page_zip) {
      ut_ad(page_is_comp(page));
      type = MLOG_ZIP_PAGE_REORGANIZE;
    } else {
      type = MLOG_PAGE_REORGANIZE;
    }

    bool opened = false;

    if (!log_compressed) {
      opened = mlog_open_and_write_index(mtr, page, index, type,
                                         page_zip ? 1 : 0, log_ptr);
    }

    /* For compressed pages write the compression level. */
    if (opened && page_zip) {
      mach_write_to_1(log_ptr, z_level);
      mlog_close(mtr, log_ptr + 1);
    }

    MONITOR_INC(MONITOR_INDEX_REORG_SUCCESSFUL);
  }
#endif /* !UNIV_HOTBACKUP */

  return (success);
}

/** Reorganizes an index page.

 IMPORTANT: On success, the caller will have to update IBUF_BITMAP_FREE
 if this is a compressed leaf page in a secondary index. This has to
 be done either within the same mini-transaction, or by invoking
 ibuf_reset_free_bits() before mtr_commit(). On uncompressed pages,
 IBUF_BITMAP_FREE is unaffected by reorganization.

 @retval true if the operation was successful
 @retval false if it is a compressed page, and recompression failed */
static bool btr_page_reorganize_block(
    bool recovery,       /*!< in: true if called in recovery:
                        locks should not be updated, i.e.,
                        there cannot exist locks on the
                        page, and a hash index should not be
                        dropped: it cannot exist */
    ulint z_level,       /*!< in: compression level to be used
                         if dealing with compressed page */
    buf_block_t *block,  /*!< in/out: B-tree page */
    dict_index_t *index, /*!< in: the index tree of the page */
    mtr_t *mtr)          /*!< in/out: mini-transaction */
{
  page_cur_t cur;
  page_cur_set_before_first(block, &cur);

  return (btr_page_reorganize_low(recovery, z_level, &cur, index, mtr));
}

/** Reorganizes an index page.

IMPORTANT: On success, the caller will have to update IBUF_BITMAP_FREE
if this is a compressed leaf page in a secondary index. This has to
be done either within the same mini-transaction, or by invoking
ibuf_reset_free_bits() before mtr_commit(). On uncompressed pages,
IBUF_BITMAP_FREE is unaffected by reorganization.

@param[in,out] cursor Page cursor
@param[in] index The index tree of the page
@param[in,out] mtr Mini-transaction
@retval true if the operation was successful
@retval false if it is a compressed page, and recompression failed */
bool btr_page_reorganize(page_cur_t *cursor, dict_index_t *index, mtr_t *mtr) {
  return (btr_page_reorganize_low(false, page_zip_level, cursor, index, mtr));
}

/** Parses a redo log record of reorganizing a page.
 @return end of log record or NULL */
byte *btr_parse_page_reorganize(
    byte *ptr,           /*!< in: buffer */
    byte *end_ptr,       /*!< in: buffer end */
    dict_index_t *index, /*!< in: record descriptor */
    bool compressed,     /*!< in: true if compressed page */
    buf_block_t *block,  /*!< in: page to be reorganized, or NULL */
    mtr_t *mtr)          /*!< in: mtr or NULL */
{
  ulint level;

  ut_ad(index != nullptr);

  /* If dealing with a compressed page the record has the
  compression level used during original compression written in
  one byte. Otherwise record is empty. */
  if (compressed) {
    if (ptr == end_ptr) {
      return (nullptr);
    }

    level = mach_read_from_1(ptr);

    ut_a(level <= 9);
    ++ptr;
  } else {
    level = page_zip_level;
  }

  if (block != nullptr) {
    btr_page_reorganize_block(true, level, block, index, mtr);
  }

  return (ptr);
}

#ifndef UNIV_HOTBACKUP
/** Empties an index page.  @see btr_page_create(). */
static void btr_page_empty(
    buf_block_t *block,       /*!< in: page to be emptied */
    page_zip_des_t *page_zip, /*!< out: compressed page, or NULL */
    dict_index_t *index,      /*!< in: index of the page */
    ulint level,              /*!< in: the B-tree level of the page */
    mtr_t *mtr)               /*!< in: mtr */
{
  page_t *page = buf_block_get_frame(block);

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));
  ut_ad(page_zip == buf_block_get_page_zip(block));
#ifdef UNIV_ZIP_DEBUG
  ut_a(!page_zip || page_zip_validate(page_zip, page, index));
#endif /* UNIV_ZIP_DEBUG */

  btr_search_drop_page_hash_index(block);

  uint16_t page_type;
  if (dict_index_is_spatial(index)) {
    page_type = FIL_PAGE_RTREE;
  } else if (dict_index_is_sdi(index)) {
    page_type = FIL_PAGE_SDI;
  } else {
    page_type = FIL_PAGE_INDEX;
  }

  /* Recreate the page: note that global data on page (possible
  segment headers, next page-field, etc.) is preserved intact */

  if (page_zip) {
    page_create_zip(block, index, level, 0, mtr, page_type);
  } else {
    page_create(block, mtr, dict_table_is_comp(index->table), page_type);
    btr_page_set_level(page, nullptr, level, mtr);
  }
}

/** Makes tree one level higher by splitting the root, and inserts
 the tuple. It is assumed that mtr contains an x-latch on the tree.
 NOTE that the operation of this function must always succeed,
 we cannot reverse it: therefore enough free disk space must be
 guaranteed to be available before this function is called.
 @return inserted record */
rec_t *btr_root_raise_and_insert(
    uint32_t flags,        /*!< in: undo logging and locking flags */
    btr_cur_t *cursor,     /*!< in: cursor at which to insert: must be
                           on the root page; when the function returns,
                           the cursor is positioned on the predecessor
                           of the inserted record */
    ulint **offsets,       /*!< out: offsets on inserted record */
    mem_heap_t **heap,     /*!< in/out: pointer to memory heap, or NULL */
    const dtuple_t *tuple, /*!< in: tuple to insert */
    mtr_t *mtr)            /*!< in: mtr */
{
  dict_index_t *index;
  page_t *root;
  page_t *new_page;
  page_no_t new_page_no;
  rec_t *rec;
  dtuple_t *node_ptr;
  ulint level;
  rec_t *node_ptr_rec;
  page_cur_t *page_cursor;
  page_zip_des_t *root_page_zip;
  page_zip_des_t *new_page_zip;
  buf_block_t *root_block;
  buf_block_t *new_block;

  root = btr_cur_get_page(cursor);
  root_block = btr_cur_get_block(cursor);
  root_page_zip = buf_block_get_page_zip(root_block);
  ut_ad(!page_is_empty(root));
  index = cursor->index;
#ifdef UNIV_ZIP_DEBUG
  ut_a(!root_page_zip || page_zip_validate(root_page_zip, root, index));
#endif /* UNIV_ZIP_DEBUG */
#ifdef UNIV_BTR_DEBUG
  if (!dict_index_is_ibuf(index)) {
    space_id_t space_id = dict_index_get_space(index);

    ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_LEAF + root,
                                space_id));
    ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_TOP + root,
                                space_id));
  }

  ut_a(dict_index_get_page(index) == page_get_page_no(root));
#endif /* UNIV_BTR_DEBUG */
  ut_ad(mtr_memo_contains_flagged(mtr, dict_index_get_lock(index),
                                  MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK) ||
        index->table->is_intrinsic());
  ut_ad(mtr_is_block_fix(mtr, root_block, MTR_MEMO_PAGE_X_FIX, index->table));

  /* Allocate a new page to the tree. Root splitting is done by first
  moving the root records to the new page, emptying the root, putting
  a node pointer to the new page, and then splitting the new page. */

  level = btr_page_get_level(root);

  new_block = btr_page_alloc(index, 0, FSP_NO_DIR, level, mtr, mtr);

  /* New page could not be allocated */
  if (!new_block) {
    return nullptr;
  }

  new_page = buf_block_get_frame(new_block);
  new_page_zip = buf_block_get_page_zip(new_block);
  ut_a(!new_page_zip == !root_page_zip);
  ut_a(!new_page_zip ||
       page_zip_get_size(new_page_zip) == page_zip_get_size(root_page_zip));

  btr_page_create(new_block, new_page_zip, index, level, mtr);

  /* Set the next node and previous node fields of new page */
  btr_page_set_next(new_page, new_page_zip, FIL_NULL, mtr);
  btr_page_set_prev(new_page, new_page_zip, FIL_NULL, mtr);

  /* Copy the records from root to the new page one by one. */

  if (false
#ifdef UNIV_ZIP_COPY
      || new_page_zip
#endif /* UNIV_ZIP_COPY */
      || !page_copy_rec_list_end(new_block, root_block,
                                 page_get_infimum_rec(root), index, mtr)) {
    ut_a(new_page_zip);

    /* Copy the page byte for byte. */
    page_zip_copy_recs(new_page_zip, new_page, root_page_zip, root, index, mtr);

    /* Update the lock table and possible hash index. */

    if (!dict_table_is_locking_disabled(index->table)) {
      lock_move_rec_list_end(new_block, root_block, page_get_infimum_rec(root));
    }

    /* Move any existing predicate locks */
    if (dict_index_is_spatial(index)) {
      lock_prdt_rec_move(new_block, root_block);
    }

    btr_search_move_or_delete_hash_entries(new_block, root_block, index);
  }

  /* If this is a pessimistic insert which is actually done to
  perform a pessimistic update then we have stored the lock
  information of the record to be inserted on the infimum of the
  root page: we cannot discard the lock structs on the root page */

  if (!dict_table_is_locking_disabled(index->table)) {
    lock_update_root_raise(new_block, root_block);
  }

  /* Create a memory heap where the node pointer is stored */
  if (!*heap) {
    *heap = mem_heap_create(100, UT_LOCATION_HERE);
  }

  rec = page_rec_get_next(page_get_infimum_rec(new_page));
  new_page_no = new_block->page.id.page_no();

  /* Build the node pointer (= node key and page address) for the
  child */
  if (dict_index_is_spatial(index)) {
    rtr_mbr_t new_mbr;

    rtr_page_cal_mbr(index, new_block, &new_mbr, *heap);
    node_ptr =
        rtr_index_build_node_ptr(index, &new_mbr, rec, new_page_no, *heap);
  } else {
    node_ptr = dict_index_build_node_ptr(index, rec, new_page_no, *heap, level);
  }
  /* The node pointer must be marked as the predefined minimum record,
  as there is no lower alphabetical limit to records in the leftmost
  node of a level: */
  dtuple_set_info_bits(node_ptr,
                       dtuple_get_info_bits(node_ptr) | REC_INFO_MIN_REC_FLAG);

  /* Rebuild the root page to get free space */
  btr_page_empty(root_block, root_page_zip, index, level + 1, mtr);

  /* Set the next node and previous node fields, although
  they should already have been set.  The previous node field
  must be FIL_NULL if root_page_zip != NULL, because the
  REC_INFO_MIN_REC_FLAG (of the first user record) will be
  set if and only if btr_page_get_prev() == FIL_NULL. */
  btr_page_set_next(root, root_page_zip, FIL_NULL, mtr);
  btr_page_set_prev(root, root_page_zip, FIL_NULL, mtr);

  page_cursor = btr_cur_get_page_cur(cursor);

  /* Insert node pointer to the root */

  page_cur_set_before_first(root_block, page_cursor);

  node_ptr_rec =
      page_cur_tuple_insert(page_cursor, node_ptr, index, offsets, heap, mtr);

  /* The root page should only contain the node pointer
  to new_page at this point.  Thus, the data should fit. */
  ut_a(node_ptr_rec);

  /* We play safe and reset the free bits for the new page */

  if (!index->is_clustered() && !index->table->is_temporary()) {
    ibuf_reset_free_bits(new_block);
  }

  /* Reposition the cursor to the child node */
  page_cur_search(new_block, index, tuple, page_cursor);

  /* Split the child and insert tuple */
  if (dict_index_is_spatial(index)) {
    /* Split rtree page and insert tuple */
    return (
        rtr_page_split_and_insert(flags, cursor, offsets, heap, tuple, mtr));
  } else {
    return (
        btr_page_split_and_insert(flags, cursor, offsets, heap, tuple, mtr));
  }
}

/** Decides if the page should be split at the convergence point of inserts
 converging to the left.
 @return true if split recommended */
bool btr_page_get_split_rec_to_left(
    btr_cur_t *cursor, /*!< in: cursor at which to insert */
    rec_t **split_rec) /*!< out: if split recommended,
                    the first record on upper half page,
                    or NULL if tuple to be inserted should
                    be first */
{
  page_t *page;
  rec_t *insert_point;
  rec_t *infimum;

  page = btr_cur_get_page(cursor);
  insert_point = btr_cur_get_rec(cursor);

  if (page_header_get_ptr(page, PAGE_LAST_INSERT) ==
      page_rec_get_next(insert_point)) {
    infimum = page_get_infimum_rec(page);

    /* If the convergence is in the middle of a page, include also
    the record immediately before the new insert to the upper
    page. Otherwise, we could repeatedly move from page to page
    lots of records smaller than the convergence point. */

    if (infimum != insert_point && page_rec_get_next(infimum) != insert_point) {
      *split_rec = insert_point;
    } else {
      *split_rec = page_rec_get_next(insert_point);
    }

    return true;
  }

  return false;
}

/** Decides if the page should be split at the convergence point of inserts
 converging to the right.
 @return true if split recommended */
bool btr_page_get_split_rec_to_right(
    btr_cur_t *cursor, /*!< in: cursor at which to insert */
    rec_t **split_rec) /*!< out: if split recommended,
                    the first record on upper half page,
                    or NULL if tuple to be inserted should
                    be first */
{
  page_t *page;
  rec_t *insert_point;

  page = btr_cur_get_page(cursor);
  insert_point = btr_cur_get_rec(cursor);

  /* We use eager heuristics: if the new insert would be right after
  the previous insert on the same page, we assume that there is a
  pattern of sequential inserts here. */

  if (page_header_get_ptr(page, PAGE_LAST_INSERT) == insert_point) {
    rec_t *next_rec;

    next_rec = page_rec_get_next(insert_point);

    if (page_rec_is_supremum(next_rec)) {
    split_at_new:
      /* Split at the new record to insert */
      *split_rec = nullptr;
    } else {
      rec_t *next_next_rec = page_rec_get_next(next_rec);
      if (page_rec_is_supremum(next_next_rec)) {
        goto split_at_new;
      }

      /* If there are >= 2 user records up from the insert
      point, split all but 1 off. We want to keep one because
      then sequential inserts can use the adaptive hash
      index, as they can do the necessary checks of the right
      search position just by looking at the records on this
      page. */

      *split_rec = next_next_rec;
    }

    return true;
  }

  return false;
}

/** Calculates a split record such that the tuple will certainly fit on
 its half-page when the split is performed. We assume in this function
 only that the cursor page has at least one user record.
 @return split record, or NULL if tuple will be the first record on
 the lower or upper half-page (determined by btr_page_tuple_smaller()) */
static rec_t *btr_page_get_split_rec(
    btr_cur_t *cursor,     /*!< in: cursor at which insert should be made */
    const dtuple_t *tuple) /*!< in: tuple to insert */
{
  page_t *page;
  page_zip_des_t *page_zip;
  ulint insert_size;
  ulint free_space;
  ulint total_data;
  ulint total_n_recs;
  ulint total_space;
  ulint incl_data;
  rec_t *ins_rec;
  rec_t *rec;
  rec_t *next_rec;
  ulint n;
  mem_heap_t *heap;
  ulint *offsets;

  page = btr_cur_get_page(cursor);

  insert_size = rec_get_converted_size(cursor->index, tuple);
  free_space = page_get_free_space_of_empty(page_is_comp(page));

  page_zip = btr_cur_get_page_zip(cursor);
  if (page_zip) {
    /* Estimate the free space of an empty compressed page. */
    ulint free_space_zip = page_zip_empty_size(cursor->index->n_fields,
                                               page_zip_get_size(page_zip));

    if (free_space > (ulint)free_space_zip) {
      free_space = (ulint)free_space_zip;
    }
  }

  /* free_space is now the free space of a created new page */

  total_data = page_get_data_size(page) + insert_size;
  total_n_recs = page_get_n_recs(page) + 1;
  ut_ad(total_n_recs >= 2);
  total_space = total_data + page_dir_calc_reserved_space(total_n_recs);

  n = 0;
  incl_data = 0;
  ins_rec = btr_cur_get_rec(cursor);
  rec = page_get_infimum_rec(page);

  heap = nullptr;
  offsets = nullptr;

  /* We start to include records to the left half, and when the
  space reserved by them exceeds half of total_space, then if
  the included records fit on the left page, they will be put there
  if something was left over also for the right page,
  otherwise the last included record will be the first on the right
  half page */

  do {
    /* Decide the next record to include */
    if (rec == ins_rec) {
      rec = nullptr; /* NULL denotes that tuple is
                  now included */
    } else if (rec == nullptr) {
      rec = page_rec_get_next(ins_rec);
    } else {
      rec = page_rec_get_next(rec);
    }

    if (rec == nullptr) {
      /* Include tuple */
      incl_data += insert_size;
    } else {
      offsets =
          rec_get_offsets(rec, cursor->index, offsets, ULINT_UNDEFINED, &heap);
      incl_data += rec_offs_size(offsets);
    }

    n++;
  } while (incl_data + page_dir_calc_reserved_space(n) < total_space / 2);

  if (incl_data + page_dir_calc_reserved_space(n) <= free_space) {
    /* The next record will be the first on
    the right half page if it is not the
    supremum record of page */

    if (rec == ins_rec) {
      rec = nullptr;

      goto func_exit;
    } else if (rec == nullptr) {
      next_rec = page_rec_get_next(ins_rec);
    } else {
      next_rec = page_rec_get_next(rec);
    }
    ut_ad(next_rec);
    if (!page_rec_is_supremum(next_rec)) {
      rec = next_rec;
    }
  }

func_exit:
  if (heap) {
    mem_heap_free(heap);
  }
  return (rec);
}

/** Returns true if the insert fits on the appropriate half-page with the
 chosen split_rec.
 @return true if fits */
[[nodiscard]] static bool btr_page_insert_fits(
    btr_cur_t *cursor,      /*!< in: cursor at which insert
                            should be made */
    const rec_t *split_rec, /*!< in: suggestion for first record
                          on upper half-page, or NULL if
                          tuple to be inserted should be first */
    ulint **offsets,        /*!< in: rec_get_offsets(
                            split_rec, cursor->index); out: garbage */
    const dtuple_t *tuple,  /*!< in: tuple to insert */
    mem_heap_t **heap)      /*!< in: temporary memory heap */
{
  page_t *page;
  ulint insert_size;
  ulint free_space;
  ulint total_data;
  ulint total_n_recs;
  const rec_t *rec;
  const rec_t *end_rec;

  page = btr_cur_get_page(cursor);

  ut_ad(!split_rec || !page_is_comp(page) == !rec_offs_comp(*offsets));
  ut_ad(!split_rec || rec_offs_validate(split_rec, cursor->index, *offsets));

  insert_size = rec_get_converted_size(cursor->index, tuple);
  free_space = page_get_free_space_of_empty(page_is_comp(page));

  /* free_space is now the free space of a created new page */

  total_data = page_get_data_size(page) + insert_size;
  total_n_recs = page_get_n_recs(page) + 1;

  /* We determine which records (from rec to end_rec, not including
  end_rec) will end up on the other half page from tuple when it is
  inserted. */

  if (split_rec == nullptr) {
    rec = page_rec_get_next(page_get_infimum_rec(page));
    end_rec = page_rec_get_next(btr_cur_get_rec(cursor));

  } else if (cmp_dtuple_rec(tuple, split_rec, cursor->index, *offsets) >= 0) {
    rec = page_rec_get_next(page_get_infimum_rec(page));
    end_rec = split_rec;
  } else {
    rec = split_rec;
    end_rec = page_get_supremum_rec(page);
  }

  if (total_data + page_dir_calc_reserved_space(total_n_recs) <= free_space) {
    /* Ok, there will be enough available space on the
    half page where the tuple is inserted */

    return (true);
  }

  while (rec != end_rec) {
    /* In this loop we calculate the amount of reserved
    space after rec is removed from page. */

    *offsets =
        rec_get_offsets(rec, cursor->index, *offsets, ULINT_UNDEFINED, heap);

    total_data -= rec_offs_size(*offsets);
    total_n_recs--;

    if (total_data + page_dir_calc_reserved_space(total_n_recs) <= free_space) {
      /* Ok, there will be enough available space on the
      half page where the tuple is inserted */

      return (true);
    }

    rec = page_rec_get_next_const(rec);
  }

  return (false);
}

/** Inserts a data tuple to a tree on a non-leaf level. It is assumed
 that mtr holds an x-latch on the tree.
 @param[in] flags undo logging and locking flags
 @param[in] index index
 @param[in] level level, must be > 0
 @param[in] tuple the record to be inserted
 @param[in] location location where called
 @param[in] mtr mtr */
void btr_insert_on_non_leaf_level(uint32_t flags, dict_index_t *index,
                                  ulint level, dtuple_t *tuple,
                                  ut::Location location, mtr_t *mtr) {
  big_rec_t *dummy_big_rec;
  btr_cur_t cursor;
  dberr_t err;
  rec_t *rec;
  mem_heap_t *heap = nullptr;
  ulint offsets_[REC_OFFS_NORMAL_SIZE];
  ulint *offsets = offsets_;
  rec_offs_init(offsets_);
  rtr_info_t rtr_info;

  ut_ad(level > 0);

  if (!dict_index_is_spatial(index)) {
    if (index->table->is_intrinsic()) {
      btr_cur_search_to_nth_level_with_no_latch(
          index, level, tuple, PAGE_CUR_LE, &cursor, __FILE__, __LINE__, mtr);
    } else {
      btr_cur_search_to_nth_level(index, level, tuple, PAGE_CUR_LE,
                                  BTR_CONT_MODIFY_TREE, &cursor, 0,
                                  location.filename, location.line, mtr);
    }
  } else {
    /* For spatial index, initialize structures to track
    its parents etc. */
    rtr_init_rtr_info(&rtr_info, false, &cursor, index, false);

    rtr_info_update_btr(&cursor, &rtr_info);

    btr_cur_search_to_nth_level(index, level, tuple, PAGE_CUR_RTREE_INSERT,
                                BTR_CONT_MODIFY_TREE, &cursor, 0,
                                location.filename, location.line, mtr);
  }

  ut_ad(cursor.flag == BTR_CUR_BINARY);

  err = btr_cur_optimistic_insert(
      flags | BTR_NO_LOCKING_FLAG | BTR_KEEP_SYS_FLAG | BTR_NO_UNDO_LOG_FLAG,
      &cursor, &offsets, &heap, tuple, &rec, &dummy_big_rec, nullptr, mtr);

  if (err == DB_FAIL) {
    err = btr_cur_pessimistic_insert(
        flags | BTR_NO_LOCKING_FLAG | BTR_KEEP_SYS_FLAG | BTR_NO_UNDO_LOG_FLAG,
        &cursor, &offsets, &heap, tuple, &rec, &dummy_big_rec, nullptr, mtr);
    ut_a(err == DB_SUCCESS);
  }

  if (heap != nullptr) {
    mem_heap_free(heap);
  }

  if (dict_index_is_spatial(index)) {
    ut_ad(cursor.rtr_info);

    rtr_clean_rtr_info(&rtr_info, true);
  }
}

/** Attaches the halves of an index page on the appropriate level in an
 index tree. */
static void btr_attach_half_pages(
    uint32_t flags,         /*!< in: undo logging and
                         locking flags */
    dict_index_t *index,    /*!< in: the index tree */
    buf_block_t *block,     /*!< in/out: page to be split */
    const rec_t *split_rec, /*!< in: first record on upper
                            half page */
    buf_block_t *new_block, /*!< in/out: the new half page */
    ulint direction,        /*!< in: FSP_UP or FSP_DOWN */
    mtr_t *mtr)             /*!< in: mtr */
{
  page_no_t prev_page_no;
  page_no_t next_page_no;
  ulint level;
  page_t *page = buf_block_get_frame(block);
  page_t *lower_page;
  page_t *upper_page;
  page_no_t lower_page_no;
  page_no_t upper_page_no;
  page_zip_des_t *lower_page_zip;
  page_zip_des_t *upper_page_zip;
  dtuple_t *node_ptr_upper;
  mem_heap_t *heap;
  buf_block_t *prev_block = nullptr;
  buf_block_t *next_block = nullptr;

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));
  ut_ad(mtr_is_block_fix(mtr, new_block, MTR_MEMO_PAGE_X_FIX, index->table));

  /* Create a memory heap where the data tuple is stored */
  heap = mem_heap_create(1024, UT_LOCATION_HERE);

  /* Based on split direction, decide upper and lower pages */
  if (direction == FSP_DOWN) {
    btr_cur_t cursor;
    ulint *offsets;

    lower_page = buf_block_get_frame(new_block);
    lower_page_no = new_block->page.id.page_no();
    lower_page_zip = buf_block_get_page_zip(new_block);
    upper_page = buf_block_get_frame(block);
    upper_page_no = block->page.id.page_no();
    upper_page_zip = buf_block_get_page_zip(block);

    /* Look up the index for the node pointer to page */
    offsets =
        btr_page_get_father_block(nullptr, heap, index, block, mtr, &cursor);

    /* Replace the address of the old child node (= page) with the
    address of the new lower half */

    btr_node_ptr_set_child_page_no(btr_cur_get_rec(&cursor),
                                   btr_cur_get_page_zip(&cursor), offsets,
                                   lower_page_no, mtr);
    mem_heap_empty(heap);
  } else {
    lower_page = buf_block_get_frame(block);
    lower_page_no = block->page.id.page_no();
    lower_page_zip = buf_block_get_page_zip(block);
    upper_page = buf_block_get_frame(new_block);
    upper_page_no = new_block->page.id.page_no();
    upper_page_zip = buf_block_get_page_zip(new_block);
  }

  /* Get the previous and next pages of page */
  prev_page_no = btr_page_get_prev(page, mtr);
  next_page_no = btr_page_get_next(page, mtr);

  const space_id_t space = block->page.id.space();

  /* for consistency, both blocks should be locked, before change */
  if (prev_page_no != FIL_NULL && direction == FSP_DOWN) {
    prev_block = btr_block_get(page_id_t(space, prev_page_no), block->page.size,
                               RW_X_LATCH, UT_LOCATION_HERE, index, mtr);
  }
  if (next_page_no != FIL_NULL && direction != FSP_DOWN) {
    next_block = btr_block_get(page_id_t(space, next_page_no), block->page.size,
                               RW_X_LATCH, UT_LOCATION_HERE, index, mtr);
  }

  /* Get the level of the split pages */
  level = btr_page_get_level(buf_block_get_frame(block));
  ut_ad(level == btr_page_get_level(buf_block_get_frame(new_block)));

  /* Build the node pointer (= node key and page address) for the upper
  half */

  node_ptr_upper =
      dict_index_build_node_ptr(index, split_rec, upper_page_no, heap, level);

  /* Insert it next to the pointer to the lower half. Note that this
  may generate recursion leading to a split on the higher level. */

  btr_insert_on_non_leaf_level(flags, index, level + 1, node_ptr_upper,
                               UT_LOCATION_HERE, mtr);

  /* Free the memory heap */
  mem_heap_free(heap);

  /* Update page links of the level */

  if (prev_block) {
#ifdef UNIV_BTR_DEBUG
    ut_a(page_is_comp(prev_block->frame) == page_is_comp(page));
    ut_a(btr_page_get_next(prev_block->frame, mtr) == block->page.id.page_no());
#endif /* UNIV_BTR_DEBUG */

    btr_page_set_next(buf_block_get_frame(prev_block),
                      buf_block_get_page_zip(prev_block), lower_page_no, mtr);
  }

  if (next_block) {
#ifdef UNIV_BTR_DEBUG
    ut_a(page_is_comp(next_block->frame) == page_is_comp(page));
    ut_a(btr_page_get_prev(next_block->frame, mtr) == page_get_page_no(page));
#endif /* UNIV_BTR_DEBUG */

    btr_page_set_prev(buf_block_get_frame(next_block),
                      buf_block_get_page_zip(next_block), upper_page_no, mtr);
  }

  if (direction == FSP_DOWN) {
    /* lower_page is new */
    btr_page_set_prev(lower_page, lower_page_zip, prev_page_no, mtr);
  } else {
    ut_ad(btr_page_get_prev(lower_page, mtr) == prev_page_no);
  }

  btr_page_set_next(lower_page, lower_page_zip, upper_page_no, mtr);
  btr_page_set_prev(upper_page, upper_page_zip, lower_page_no, mtr);

  if (direction != FSP_DOWN) {
    /* upper_page is new */
    btr_page_set_next(upper_page, upper_page_zip, next_page_no, mtr);
  } else {
    ut_ad(btr_page_get_next(upper_page, mtr) == next_page_no);
  }
}

/** Determine if a tuple is smaller than any record on the page.
 @return true if smaller */
[[nodiscard]] static bool btr_page_tuple_smaller(
    btr_cur_t *cursor,     /*!< in: b-tree cursor */
    const dtuple_t *tuple, /*!< in: tuple to consider */
    ulint **offsets,       /*!< in/out: temporary storage */
    ulint n_uniq,          /*!< in: number of unique fields
                           in the index page records */
    mem_heap_t **heap)     /*!< in/out: heap for offsets */
{
  buf_block_t *block;
  const rec_t *first_rec;
  page_cur_t pcur;

  /* Read the first user record in the page. */
  block = btr_cur_get_block(cursor);
  page_cur_set_before_first(block, &pcur);
  page_cur_move_to_next(&pcur);
  first_rec = page_cur_get_rec(&pcur);

  *offsets = rec_get_offsets(first_rec, cursor->index, *offsets, n_uniq, heap);

  return (cmp_dtuple_rec(tuple, first_rec, cursor->index, *offsets) < 0);
}

/** Insert the tuple into the right sibling page, if the cursor is at the end
of a page.
@param[in]      flags   Undo logging and locking flags
@param[in,out]  cursor  Cursor at which to insert; when the function succeeds,
                        the cursor is positioned before the insert point.
@param[out]     offsets Offsets on inserted record
@param[in,out]  heap    Memory heap for allocating offsets
@param[in]      tuple   Tuple to insert
@param[in,out]  mtr     Mini-transaction
@return inserted record (first record on the right sibling page);
        the cursor will be positioned on the page infimum
@retval NULL if the operation was not performed */
static rec_t *btr_insert_into_right_sibling(uint32_t flags, btr_cur_t *cursor,
                                            ulint **offsets, mem_heap_t *heap,
                                            const dtuple_t *tuple, mtr_t *mtr) {
  buf_block_t *block = btr_cur_get_block(cursor);
  page_t *page = buf_block_get_frame(block);
  page_no_t next_page_no = btr_page_get_next(page, mtr);

  ut_ad(cursor->index->table->is_intrinsic() ||
        mtr_memo_contains_flagged(mtr, dict_index_get_lock(cursor->index),
                                  MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK));
  ut_ad(
      mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, cursor->index->table));
  ut_ad(heap);

  if (next_page_no == FIL_NULL ||
      !page_rec_is_supremum(page_rec_get_next(btr_cur_get_rec(cursor)))) {
    return (nullptr);
  }

  page_cur_t next_page_cursor;
  buf_block_t *next_block;
  page_t *next_page;
  btr_cur_t next_father_cursor;
  rec_t *rec = nullptr;
  ulint max_size;

  const space_id_t space = block->page.id.space();

  next_block = btr_block_get(page_id_t(space, next_page_no), block->page.size,
                             RW_X_LATCH, UT_LOCATION_HERE, cursor->index, mtr);
  next_page = buf_block_get_frame(next_block);

  bool is_leaf = page_is_leaf(next_page);

  btr_page_get_father(cursor->index, next_block, mtr, &next_father_cursor);

  page_cur_search(next_block, cursor->index, tuple, PAGE_CUR_LE,
                  &next_page_cursor);

  max_size = page_get_max_insert_size_after_reorganize(next_page, 1);

  /* Extends gap lock for the next page */
  if (!dict_table_is_locking_disabled(cursor->index->table)) {
    lock_update_split_point(next_block, block);
  }

  rec = page_cur_tuple_insert(&next_page_cursor, tuple, cursor->index, offsets,
                              &heap, mtr);

  if (rec == nullptr) {
    if (is_leaf && next_block->page.size.is_compressed() &&
        !cursor->index->is_clustered() &&
        !cursor->index->table->is_temporary()) {
      /* Reset the IBUF_BITMAP_FREE bits, because
      page_cur_tuple_insert() will have attempted page
      reorganize before failing. */
      ibuf_reset_free_bits(next_block);
    }
    return (nullptr);
  }

  dberr_t err;
  ulint level = btr_page_get_level(next_page);

  /* adjust cursor position */
  *btr_cur_get_page_cur(cursor) = next_page_cursor;

  ut_ad(btr_cur_get_rec(cursor) == page_get_infimum_rec(next_page));
  ut_ad(page_rec_get_next(page_get_infimum_rec(next_page)) == rec);

  /* We have to change the parent node pointer */

  auto compressed = btr_cur_pessimistic_delete(&err, true, &next_father_cursor,
                                               BTR_CREATE_FLAG, false, 0, 0, 0,
                                               mtr, nullptr, nullptr);

  ut_a(err == DB_SUCCESS);

  if (!compressed) {
    btr_cur_compress_if_useful(&next_father_cursor, false, mtr);
  }

  dtuple_t *node_ptr = dict_index_build_node_ptr(
      cursor->index, rec, next_block->page.id.page_no(), heap, level);

  btr_insert_on_non_leaf_level(flags, cursor->index, level + 1, node_ptr,
                               UT_LOCATION_HERE, mtr);

  ut_ad(rec_offs_validate(rec, cursor->index, *offsets));

  if (is_leaf && !cursor->index->is_clustered() &&
      !cursor->index->table->is_temporary()) {
    /* Update the free bits of the B-tree page in the
    insert buffer bitmap. */

    if (next_block->page.size.is_compressed()) {
      ibuf_update_free_bits_zip(next_block, mtr);
    } else {
      ibuf_update_free_bits_if_full(
          next_block, max_size, rec_offs_size(*offsets) + PAGE_DIR_SLOT_SIZE);
    }
  }

  return (rec);
}

/** Splits an index page to halves and inserts the tuple. It is assumed
 that mtr holds an x-latch to the index tree. NOTE: the tree x-latch is
 released within this function! NOTE that the operation of this
 function must always succeed, we cannot reverse it: therefore enough
 free disk space (2 pages) must be guaranteed to be available before
 this function is called.
 @return inserted record */
rec_t *btr_page_split_and_insert(
    uint32_t flags,        /*!< in: undo logging and locking flags */
    btr_cur_t *cursor,     /*!< in: cursor at which to insert; when the
                           function returns, the cursor is positioned
                           on the predecessor of the inserted record */
    ulint **offsets,       /*!< out: offsets on inserted record */
    mem_heap_t **heap,     /*!< in/out: pointer to memory heap, or NULL */
    const dtuple_t *tuple, /*!< in: tuple to insert */
    mtr_t *mtr)            /*!< in: mtr */
{
  buf_block_t *block;
  page_t *page;
  page_zip_des_t *page_zip;
  page_no_t page_no;
  byte direction;
  page_no_t hint_page_no;
  buf_block_t *new_block;
  page_t *new_page;
  page_zip_des_t *new_page_zip;
  rec_t *split_rec;
  buf_block_t *left_block;
  buf_block_t *right_block;
  buf_block_t *insert_block;
  page_cur_t *page_cursor;
  rec_t *first_rec;
  byte *buf = nullptr; /* remove warning */
  rec_t *move_limit;
  bool insert_will_fit;
  bool insert_left;
  ulint n_iterations = 0;
  rec_t *rec;
  ulint n_uniq;
  dict_index_t *index;

  index = cursor->index;

  if (dict_index_is_spatial(index)) {
    /* Split rtree page and update parent */
    return (
        rtr_page_split_and_insert(flags, cursor, offsets, heap, tuple, mtr));
  }

  if (!*heap) {
    *heap = mem_heap_create(1024, UT_LOCATION_HERE);
  }
  n_uniq = dict_index_get_n_unique_in_tree(cursor->index);
func_start:
  ut_ad(tuple->m_heap != *heap);
  mem_heap_empty(*heap);
  *offsets = nullptr;

  ut_ad(mtr_memo_contains_flagged(mtr, dict_index_get_lock(cursor->index),
                                  MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK) ||
        cursor->index->table->is_intrinsic());
  ut_ad(!dict_index_is_online_ddl(cursor->index) || (flags & BTR_CREATE_FLAG) ||
        cursor->index->is_clustered());
  ut_ad(rw_lock_own_flagged(dict_index_get_lock(cursor->index),
                            RW_LOCK_FLAG_X | RW_LOCK_FLAG_SX) ||
        cursor->index->table->is_intrinsic());

  block = btr_cur_get_block(cursor);
  page = buf_block_get_frame(block);
  page_zip = buf_block_get_page_zip(block);

  ut_ad(
      mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, cursor->index->table));
  ut_ad(!page_is_empty(page));

  /* try to insert to the next page if possible before split */
  rec =
      btr_insert_into_right_sibling(flags, cursor, offsets, *heap, tuple, mtr);

  if (rec != nullptr) {
    return (rec);
  }

  page_no = block->page.id.page_no();

  /* 1. Decide the split record; split_rec == NULL means that the
  tuple to be inserted should be the first record on the upper
  half-page */
  insert_left = false;

  if (n_iterations > 0) {
    direction = FSP_UP;
    hint_page_no = page_no + 1;
    split_rec = btr_page_get_split_rec(cursor, tuple);

    if (split_rec == nullptr) {
      insert_left =
          btr_page_tuple_smaller(cursor, tuple, offsets, n_uniq, heap);
    }
  } else if (btr_page_get_split_rec_to_right(cursor, &split_rec)) {
    direction = FSP_UP;
    hint_page_no = page_no + 1;

  } else if (btr_page_get_split_rec_to_left(cursor, &split_rec)) {
    direction = FSP_DOWN;
    hint_page_no = page_no - 1;
    ut_ad(split_rec);
  } else {
    direction = FSP_UP;
    hint_page_no = page_no + 1;

    /* If there is only one record in the index page, we
    can't split the node in the middle by default. We need
    to determine whether the new record will be inserted
    to the left or right. */

    if (page_get_n_recs(page) > 1) {
      split_rec = page_get_middle_rec(page);
    } else if (btr_page_tuple_smaller(cursor, tuple, offsets, n_uniq, heap)) {
      split_rec = page_rec_get_next(page_get_infimum_rec(page));
    } else {
      split_rec = nullptr;
    }
  }

  /* 2. Allocate a new page to the index */
  new_block = btr_page_alloc(cursor->index, hint_page_no, direction,
                             btr_page_get_level(page), mtr, mtr);

  /* New page could not be allocated */
  if (!new_block) {
    return nullptr;
  }

  new_page = buf_block_get_frame(new_block);
  new_page_zip = buf_block_get_page_zip(new_block);
  btr_page_create(new_block, new_page_zip, cursor->index,
                  btr_page_get_level(page), mtr);

  /* 3. Calculate the first record on the upper half-page, and the
  first record (move_limit) on original page which ends up on the
  upper half */

  if (split_rec) {
    first_rec = move_limit = split_rec;

    *offsets =
        rec_get_offsets(split_rec, cursor->index, *offsets, n_uniq, heap);

    insert_left = cmp_dtuple_rec(tuple, split_rec, cursor->index, *offsets) < 0;

    if (!insert_left && new_page_zip && n_iterations > 0) {
      /* If a compressed page has already been split,
      avoid further splits by inserting the record
      to an empty page. */
      split_rec = nullptr;
      goto insert_empty;
    }
  } else if (insert_left) {
    ut_a(n_iterations > 0);
    first_rec = page_rec_get_next(page_get_infimum_rec(page));
    move_limit = page_rec_get_next(btr_cur_get_rec(cursor));
  } else {
  insert_empty:
    ut_ad(!split_rec);
    ut_ad(!insert_left);
    buf = ut::new_arr_withkey<byte>(
        UT_NEW_THIS_FILE_PSI_KEY,
        ut::Count{rec_get_converted_size(cursor->index, tuple)});

    first_rec = rec_convert_dtuple_to_rec(buf, cursor->index, tuple);
    move_limit = page_rec_get_next(btr_cur_get_rec(cursor));
  }

  /* 4. Do first the modifications in the tree structure */

  btr_attach_half_pages(flags, cursor->index, block, first_rec, new_block,
                        direction, mtr);

  /* If the split is made on the leaf level and the insert will fit
  on the appropriate half-page, we may release the tree x-latch.
  We can then move the records after releasing the tree latch,
  thus reducing the tree latch contention. */

  if (split_rec) {
    insert_will_fit =
        !new_page_zip &&
        btr_page_insert_fits(cursor, split_rec, offsets, tuple, heap);
  } else {
    if (!insert_left) {
      ut::delete_arr(buf);
      buf = nullptr;
    }

    insert_will_fit =
        !new_page_zip &&
        btr_page_insert_fits(cursor, nullptr, offsets, tuple, heap);
  }

  if (!srv_read_only_mode && !cursor->index->table->is_intrinsic() &&
      insert_will_fit && page_is_leaf(page) &&
      !dict_index_is_online_ddl(cursor->index)) {
    mtr->memo_release(dict_index_get_lock(cursor->index),
                      MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK);

    /* NOTE: We cannot release root block latch here, because it
    has segment header and already modified in most of cases.*/
  }

  /* 5. Move then the records to the new page */
  if (direction == FSP_DOWN) {
    /*          fputs("Split left\n", stderr); */

    if (false
#ifdef UNIV_ZIP_COPY
        || page_zip
#endif /* UNIV_ZIP_COPY */
        || !page_move_rec_list_start(new_block, block, move_limit,
                                     cursor->index, mtr)) {
      /* For some reason, compressing new_page failed,
      even though it should contain fewer records than
      the original page.  Copy the page byte for byte
      and then delete the records from both pages
      as appropriate.  Deleting will always succeed. */
      ut_a(new_page_zip);

      page_zip_copy_recs(new_page_zip, new_page, page_zip, page, cursor->index,
                         mtr);
      page_delete_rec_list_end(move_limit - page + new_page, new_block,
                               cursor->index, ULINT_UNDEFINED, ULINT_UNDEFINED,
                               mtr);

      /* Update the lock table and possible hash index. */

      if (!dict_table_is_locking_disabled(cursor->index->table)) {
        lock_move_rec_list_start(new_block, block, move_limit,
                                 new_page + PAGE_NEW_INFIMUM);
      }

      btr_search_move_or_delete_hash_entries(new_block, block, cursor->index);

      /* Delete the records from the source page. */

      page_delete_rec_list_start(move_limit, block, cursor->index, mtr);
    }

    left_block = new_block;
    right_block = block;

    if (!dict_table_is_locking_disabled(cursor->index->table)) {
      lock_update_split_left(right_block, left_block);
    }
  } else {
    /*          fputs("Split right\n", stderr); */

    if (false
#ifdef UNIV_ZIP_COPY
        || page_zip
#endif /* UNIV_ZIP_COPY */
        || !page_move_rec_list_end(new_block, block, move_limit, cursor->index,
                                   mtr)) {
      /* For some reason, compressing new_page failed,
      even though it should contain fewer records than
      the original page.  Copy the page byte for byte
      and then delete the records from both pages
      as appropriate.  Deleting will always succeed. */
      ut_a(new_page_zip);

      page_zip_copy_recs(new_page_zip, new_page, page_zip, page, cursor->index,
                         mtr);
      page_delete_rec_list_start(move_limit - page + new_page, new_block,
                                 cursor->index, mtr);

      /* Update the lock table and possible hash index. */
      if (!dict_table_is_locking_disabled(cursor->index->table)) {
        lock_move_rec_list_end(new_block, block, move_limit);
      }

      ut_ad(!dict_index_is_spatial(index));

      btr_search_move_or_delete_hash_entries(new_block, block, cursor->index);

      /* Delete the records from the source page. */

      page_delete_rec_list_end(move_limit, block, cursor->index,
                               ULINT_UNDEFINED, ULINT_UNDEFINED, mtr);
    }

    left_block = block;
    right_block = new_block;

    if (!dict_table_is_locking_disabled(cursor->index->table)) {
      lock_update_split_right(right_block, left_block);
    }
  }

#ifdef UNIV_ZIP_DEBUG
  if (page_zip) {
    ut_a(page_zip_validate(page_zip, page, cursor->index));
    ut_a(page_zip_validate(new_page_zip, new_page, cursor->index));
  }
#endif /* UNIV_ZIP_DEBUG */

  /* At this point, split_rec, move_limit and first_rec may point
  to garbage on the old page. */

  /* 6. The split and the tree modification is now completed. Decide the
  page where the tuple should be inserted */

  if (insert_left) {
    insert_block = left_block;
  } else {
    insert_block = right_block;
  }

  /* 7. Reposition the cursor for insert and try insertion */
  page_cursor = btr_cur_get_page_cur(cursor);

  page_cur_search(insert_block, cursor->index, tuple, page_cursor);

  rec = page_cur_tuple_insert(page_cursor, tuple, cursor->index, offsets, heap,
                              mtr);

#ifdef UNIV_ZIP_DEBUG
  {
    page_t *insert_page = buf_block_get_frame(insert_block);

    page_zip_des_t *insert_page_zip = buf_block_get_page_zip(insert_block);

    ut_a(!insert_page_zip ||
         page_zip_validate(insert_page_zip, insert_page, cursor->index));
  }
#endif /* UNIV_ZIP_DEBUG */

  if (rec != nullptr) {
    goto func_exit;
  }

  /* 8. If insert did not fit, try page reorganization.
  For compressed pages, page_cur_tuple_insert() will have
  attempted this already. */

  if (page_cur_get_page_zip(page_cursor) ||
      !btr_page_reorganize(page_cursor, cursor->index, mtr)) {
    goto insert_failed;
  }

  rec = page_cur_tuple_insert(page_cursor, tuple, cursor->index, offsets, heap,
                              mtr);

  if (rec == nullptr) {
    /* The insert did not fit on the page: loop back to the
    start of the function for a new split */
  insert_failed:
    /* We play safe and reset the free bits for new_page */
    if (!cursor->index->is_clustered() &&
        !cursor->index->table->is_temporary()) {
      ibuf_reset_free_bits(new_block);
      ibuf_reset_free_bits(block);
    }

    n_iterations++;
    ut_ad(n_iterations < 2 || buf_block_get_page_zip(insert_block));
    ut_ad(!insert_will_fit);

    goto func_start;
  }

func_exit:
  /* Insert fit on the page: update the free bits for the
  left and right pages in the same mtr */

  if (!cursor->index->is_clustered() && !cursor->index->table->is_temporary() &&
      page_is_leaf(page)) {
    ibuf_update_free_bits_for_two_pages_low(left_block, right_block, mtr);
  }

  MONITOR_INC(MONITOR_INDEX_SPLIT);

  ut_ad(page_validate(buf_block_get_frame(left_block), cursor->index));
  ut_ad(page_validate(buf_block_get_frame(right_block), cursor->index));

  ut_ad(!rec || rec_offs_validate(rec, cursor->index, *offsets));
  return (rec);
}

/** Removes a page from the level list of pages.
@param[in] space Space where removed
@param[in] page_size Page size
@param[in,out] page Page to remove
@param[in] index Index tree
@param[in,out] mtr Mini-transaction */
static void btr_level_list_remove(space_id_t space,
                                  const page_size_t &page_size, page_t *page,
                                  const dict_index_t *index, mtr_t *mtr) {
  ut_ad(page != nullptr);
  ut_ad(mtr != nullptr);
  ut_ad(mtr_is_page_fix(mtr, page, MTR_MEMO_PAGE_X_FIX, index->table));
  ut_ad(space == page_get_space_id(page));
  /* Get the previous and next page numbers of page */

  const page_no_t prev_page_no = btr_page_get_prev(page, mtr);
  const page_no_t next_page_no = btr_page_get_next(page, mtr);

  /* Update page links of the level */

  if (prev_page_no != FIL_NULL) {
    buf_block_t *prev_block =
        btr_block_get(page_id_t(space, prev_page_no), page_size, RW_X_LATCH,
                      UT_LOCATION_HERE, index, mtr);

    page_t *prev_page = buf_block_get_frame(prev_block);
#ifdef UNIV_BTR_DEBUG
    ut_a(page_is_comp(prev_page) == page_is_comp(page));
    ut_a(btr_page_get_next(prev_page, mtr) == page_get_page_no(page));
#endif /* UNIV_BTR_DEBUG */

    btr_page_set_next(prev_page, buf_block_get_page_zip(prev_block),
                      next_page_no, mtr);
  }

  if (next_page_no != FIL_NULL) {
    buf_block_t *next_block =
        btr_block_get(page_id_t(space, next_page_no), page_size, RW_X_LATCH,
                      UT_LOCATION_HERE, index, mtr);

    page_t *next_page = buf_block_get_frame(next_block);
#ifdef UNIV_BTR_DEBUG
    ut_a(page_is_comp(next_page) == page_is_comp(page));
    ut_a(btr_page_get_prev(next_page, mtr) == page_get_page_no(page));
#endif /* UNIV_BTR_DEBUG */

    btr_page_set_prev(next_page, buf_block_get_page_zip(next_block),
                      prev_page_no, mtr);
  }
}

/** Writes the redo log record for setting an index record as the predefined
 minimum record. */
static inline void btr_set_min_rec_mark_log(
    rec_t *rec,     /*!< in: record */
    mlog_id_t type, /*!< in: MLOG_COMP_REC_MIN_MARK or
                    MLOG_REC_MIN_MARK */
    mtr_t *mtr)     /*!< in: mtr */
{
  mlog_write_initial_log_record(rec, type, mtr);

  /* Write rec offset as a 2-byte ulint */
  mlog_catenate_ulint(mtr, page_offset(rec), MLOG_2BYTES);
}
#else  /* !UNIV_HOTBACKUP */
static inline void btr_set_min_rec_mark_log(rec_t *rec, mlog_id_t type,
                                            mtr_t *mtr) {}
#endif /* !UNIV_HOTBACKUP */

/** Parses the redo log record for setting an index record as the predefined
 minimum record.
 @return end of log record or NULL */
byte *btr_parse_set_min_rec_mark(
    byte *ptr,     /*!< in: buffer */
    byte *end_ptr, /*!< in: buffer end */
    ulint comp,    /*!< in: nonzero=compact page format */
    page_t *page,  /*!< in: page or NULL */
    mtr_t *mtr)    /*!< in: mtr or NULL */
{
  rec_t *rec;

  if (end_ptr < ptr + 2) {
    return (nullptr);
  }

  if (page) {
    ut_a(!page_is_comp(page) == !comp);

    rec = page + mach_read_from_2(ptr);

    btr_set_min_rec_mark(rec, mtr);
  }

  return (ptr + 2);
}

/** Sets a record as the predefined minimum record.
@param[in,out] rec Record
@param[in] mtr Mini-transaction
*/
void btr_set_min_rec_mark(rec_t *rec, mtr_t *mtr) {
  ulint info_bits;

  if (page_rec_is_comp(rec)) {
    info_bits = rec_get_info_bits(rec, true);

    rec_set_info_bits_new(rec, info_bits | REC_INFO_MIN_REC_FLAG);

    btr_set_min_rec_mark_log(rec, MLOG_COMP_REC_MIN_MARK, mtr);
  } else {
    info_bits = rec_get_info_bits(rec, false);

    rec_set_info_bits_old(rec, info_bits | REC_INFO_MIN_REC_FLAG);

    btr_set_min_rec_mark_log(rec, MLOG_REC_MIN_MARK, mtr);
  }
}

#ifndef UNIV_HOTBACKUP
/** Deletes on the upper level the node pointer to a page.
@param[in] index Index tree
@param[in] block Page whose node pointer is deleted
@param[in] mtr Mini-transaction
*/
void btr_node_ptr_delete(dict_index_t *index, buf_block_t *block, mtr_t *mtr) {
  btr_cur_t cursor;
  dberr_t err;

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));

  /* Delete node pointer on father page */
  btr_page_get_father(index, block, mtr, &cursor);

  bool compressed =
      btr_cur_pessimistic_delete(&err, true, &cursor, BTR_CREATE_FLAG, false, 0,
                                 0, 0, mtr, nullptr, nullptr);
  ut_a(err == DB_SUCCESS);

  if (!compressed) {
    btr_cur_compress_if_useful(&cursor, false, mtr);
  }
}

/** If page is the only on its level, this function moves its records to the
 father page, thus reducing the tree height.
 @return father block */
static buf_block_t *btr_lift_page_up(
    dict_index_t *index, /*!< in: index tree */
    buf_block_t *block,  /*!< in: page which is the only on its level;
                         must not be empty: use
                         btr_discard_only_page_on_level if the last
                         record from the page should be removed */
    mtr_t *mtr)          /*!< in: mtr */
{
  buf_block_t *father_block;
  page_t *father_page;
  ulint page_level;
  page_zip_des_t *father_page_zip;
  page_t *page = buf_block_get_frame(block);
  page_no_t root_page_no;
  buf_block_t *blocks[BTR_MAX_LEVELS];
  ulint n_blocks; /*!< last used index in blocks[] */
  ulint i;
  bool lift_father_up;
  buf_block_t *block_orig = block;

  ut_ad(btr_page_get_prev(page, mtr) == FIL_NULL);
  ut_ad(btr_page_get_next(page, mtr) == FIL_NULL);
  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));

  page_level = btr_page_get_level(page);
  root_page_no = dict_index_get_page(index);

  {
    btr_cur_t cursor;
    ulint *offsets = nullptr;
    mem_heap_t *heap = mem_heap_create(
        sizeof(*offsets) * (REC_OFFS_HEADER_SIZE + 1 + 1 + index->n_fields),
        UT_LOCATION_HERE);
    buf_block_t *b;

    if (dict_index_is_spatial(index)) {
      offsets = rtr_page_get_father_block(nullptr, heap, index, block, mtr,
                                          nullptr, &cursor);
    } else {
      offsets =
          btr_page_get_father_block(offsets, heap, index, block, mtr, &cursor);
    }
    father_block = btr_cur_get_block(&cursor);
    father_page_zip = buf_block_get_page_zip(father_block);
    father_page = buf_block_get_frame(father_block);

    n_blocks = 0;

    /* Store all ancestor pages so we can reset their
    levels later on.  We have to do all the searches on
    the tree now because later on, after we've replaced
    the first level, the tree is in an inconsistent state
    and can not be searched. */
    for (b = father_block; b->page.id.page_no() != root_page_no;) {
      ut_a(n_blocks < BTR_MAX_LEVELS);

      if (dict_index_is_spatial(index)) {
        offsets = rtr_page_get_father_block(nullptr, heap, index, b, mtr,
                                            nullptr, &cursor);
      } else {
        offsets =
            btr_page_get_father_block(offsets, heap, index, b, mtr, &cursor);
      }

      blocks[n_blocks++] = b = btr_cur_get_block(&cursor);
    }

    lift_father_up = (n_blocks && page_level == 0);
    if (lift_father_up) {
      /* The father page also should be the only on its level (not
      root). We should lift up the father page at first.
      Because the leaf page should be lifted up only for root page.
      The freeing page is based on page_level (==0 or !=0)
      to choose segment. If the page_level is changed ==0 from !=0,
      later freeing of the page doesn't find the page allocation
      to be freed.*/

      block = father_block;
      page = buf_block_get_frame(block);
      page_level = btr_page_get_level(page);

      ut_ad(btr_page_get_prev(page, mtr) == FIL_NULL);
      ut_ad(btr_page_get_next(page, mtr) == FIL_NULL);
      ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));

      father_block = blocks[0];
      father_page_zip = buf_block_get_page_zip(father_block);
      father_page = buf_block_get_frame(father_block);
    }

    mem_heap_free(heap);
  }

  btr_search_drop_page_hash_index(block);

  /* Make the father empty */
  btr_page_empty(father_block, father_page_zip, index, page_level, mtr);
  page_level++;

  /* Copy the records to the father page one by one. */
  if (false
#ifdef UNIV_ZIP_COPY
      || father_page_zip
#endif /* UNIV_ZIP_COPY */
      || !page_copy_rec_list_end(father_block, block,
                                 page_get_infimum_rec(page), index, mtr)) {
    const page_zip_des_t *page_zip = buf_block_get_page_zip(block);
    ut_a(father_page_zip);
    ut_a(page_zip);

    /* Copy the page byte for byte. */
    page_zip_copy_recs(father_page_zip, father_page, page_zip, page, index,
                       mtr);

    /* Update the lock table and possible hash index. */

    if (!dict_table_is_locking_disabled(index->table)) {
      lock_move_rec_list_end(father_block, block, page_get_infimum_rec(page));
    }

    /* Also update the predicate locks */
    if (dict_index_is_spatial(index)) {
      lock_prdt_rec_move(father_block, block);
    }

    btr_search_move_or_delete_hash_entries(father_block, block, index);
  }

  if (!dict_table_is_locking_disabled(index->table)) {
    /* Free predicate page locks on the block */
    if (dict_index_is_spatial(index)) {
      locksys::Shard_latch_guard guard{UT_LOCATION_HERE, block->get_page_id()};
      lock_prdt_page_free_from_discard(block, lock_sys->prdt_page_hash);
    }
    lock_update_copy_and_discard(father_block, block);
  }

  /* Go upward to root page, decrementing levels by one. */
  for (i = lift_father_up ? 1 : 0; i < n_blocks; i++, page_level++) {
    page_t *page = buf_block_get_frame(blocks[i]);
    page_zip_des_t *page_zip = buf_block_get_page_zip(blocks[i]);

    ut_ad(btr_page_get_level(page) == page_level + 1);

    btr_page_set_level(page, page_zip, page_level, mtr);
#ifdef UNIV_ZIP_DEBUG
    ut_a(!page_zip || page_zip_validate(page_zip, page, index));
#endif /* UNIV_ZIP_DEBUG */
  }

  if (dict_index_is_spatial(index)) {
    rtr_check_discard_page(index, nullptr, block);
  }

  /* Free the file page */
  btr_page_free(index, block, mtr);

  /* We play it safe and reset the free bits for the father */
  if (!index->is_clustered() && !index->table->is_temporary()) {
    ibuf_reset_free_bits(father_block);
  }
  ut_ad(page_validate(father_page, index));
  ut_d(btr_check_node_ptr(index, father_block, mtr));

  return (lift_father_up ? block_orig : father_block);
}

bool btr_compress(btr_cur_t *cursor, bool adjust, mtr_t *mtr) {
  dict_index_t *index;
  space_id_t space;
  page_no_t left_page_no;
  page_no_t right_page_no;
  buf_block_t *merge_block;
  page_t *merge_page = nullptr;
  page_zip_des_t *merge_page_zip;
  bool is_left;
  buf_block_t *block;
  page_t *page;
  btr_cur_t father_cursor;
  mem_heap_t *heap;
  ulint *offsets;
  ulint nth_rec = 0; /* remove bogus warning */
  bool mbr_changed = false;
#ifdef UNIV_DEBUG
  bool leftmost_child;
#endif
  DBUG_TRACE;

  block = btr_cur_get_block(cursor);
  page = btr_cur_get_page(cursor);
  index = cursor->index;

  btr_assert_not_corrupted(block, index);

#ifdef UNIV_DEBUG
  if (dict_index_is_spatial(index)) {
    ut_ad(mtr_memo_contains_flagged(mtr, dict_index_get_lock(index),
                                    MTR_MEMO_X_LOCK));
  } else {
    ut_ad(mtr_memo_contains_flagged(mtr, dict_index_get_lock(index),
                                    MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK) ||
          index->table->is_intrinsic());
  }
#endif /* UNIV_DEBUG */

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));
  space = dict_index_get_space(index);

  const page_size_t page_size(dict_table_page_size(index->table));

  MONITOR_INC(MONITOR_INDEX_MERGE_ATTEMPTS);

  left_page_no = btr_page_get_prev(page, mtr);
  right_page_no = btr_page_get_next(page, mtr);

#ifdef UNIV_DEBUG
  if (!page_is_leaf(page) && left_page_no == FIL_NULL) {
    ut_a(REC_INFO_MIN_REC_FLAG &
         rec_get_info_bits(page_rec_get_next(page_get_infimum_rec(page)),
                           page_is_comp(page)));
  }
#endif /* UNIV_DEBUG */

  heap = mem_heap_create(100, UT_LOCATION_HERE);

  if (dict_index_is_spatial(index)) {
    offsets = rtr_page_get_father_block(nullptr, heap, index, block, mtr,
                                        cursor, &father_cursor);
    ut_ad(cursor->page_cur.block->page.id.page_no() ==
          block->page.id.page_no());
    rec_t *my_rec = father_cursor.page_cur.rec;

    page_no_t page_no = btr_node_ptr_get_child_page_no(my_rec, offsets);

    if (page_no != block->page.id.page_no()) {
      ib::info(ER_IB_MSG_32) << "father positioned on page " << page_no
                             << "instead of " << block->page.id.page_no();
      offsets = btr_page_get_father_block(nullptr, heap, index, block, mtr,
                                          &father_cursor);
    }
  } else {
    offsets = btr_page_get_father_block(nullptr, heap, index, block, mtr,
                                        &father_cursor);
  }

  if (adjust) {
    nth_rec = page_rec_get_n_recs_before(btr_cur_get_rec(cursor));
    ut_ad(nth_rec > 0);
  }

  if (left_page_no == FIL_NULL && right_page_no == FIL_NULL) {
    /* The page is the only one on the level, lift the records
    to the father */

    merge_block = btr_lift_page_up(index, block, mtr);
    goto func_exit;
  }

  ut_d(leftmost_child =
           left_page_no != FIL_NULL &&
           (page_rec_get_next(page_get_infimum_rec(btr_cur_get_page(
                &father_cursor))) == btr_cur_get_rec(&father_cursor)));

  /* Decide the page to which we try to merge and which will inherit
  the locks */

  is_left = btr_can_merge_with_page(cursor, left_page_no, &merge_block, mtr);

  DBUG_EXECUTE_IF("ib_always_merge_right", is_left = false;);
retry:
  if (!is_left &&
      !btr_can_merge_with_page(cursor, right_page_no, &merge_block, mtr)) {
    if (!merge_block) {
      merge_page = nullptr;
    }
    goto err_exit;
  }

  merge_page = buf_block_get_frame(merge_block);

#ifdef UNIV_BTR_DEBUG
  if (is_left) {
    ut_a(btr_page_get_next(merge_page, mtr) == block->page.id.page_no());
  } else {
    ut_a(btr_page_get_prev(merge_page, mtr) == block->page.id.page_no());
  }
#endif /* UNIV_BTR_DEBUG */

#ifdef UNIV_GIS_DEBUG
  if (dict_index_is_spatial(index)) {
    if (is_left) {
      fprintf(stderr, "GIS_DIAG: merge left  %ld to %ld \n",
              (long)block->page.id.page_no(), left_page_no);
    } else {
      fprintf(stderr, "GIS_DIAG: merge right %ld to %ld\n",
              (long)block->page.id.page_no(), right_page_no);
    }
  }
#endif /* UNIV_GIS_DEBUG */

  ut_ad(page_validate(merge_page, index));

  merge_page_zip = buf_block_get_page_zip(merge_block);
#ifdef UNIV_ZIP_DEBUG
  if (merge_page_zip) {
    const page_zip_des_t *page_zip = buf_block_get_page_zip(block);
    ut_a(page_zip);
    ut_a(page_zip_validate(merge_page_zip, merge_page, index));
    ut_a(page_zip_validate(page_zip, page, index));
  }
#endif /* UNIV_ZIP_DEBUG */

  /* Move records to the merge page */
  if (is_left) {
    btr_cur_t cursor2;
    rtr_mbr_t new_mbr;
    ulint *offsets2 = nullptr;

    /* For rtree, we need to update father's mbr. */
    if (dict_index_is_spatial(index)) {
      /* We only support merge pages with the same parent
      page */
      if (!rtr_check_same_block(index, &cursor2,
                                btr_cur_get_block(&father_cursor), merge_block,
                                heap)) {
        is_left = false;
        goto retry;
      }

      /* Set rtr_info for cursor2, since it is
      necessary in recursive page merge. */
      cursor2.rtr_info = cursor->rtr_info;
      cursor2.tree_height = cursor->tree_height;

      offsets2 = rec_get_offsets(btr_cur_get_rec(&cursor2), index, nullptr,
                                 ULINT_UNDEFINED, &heap);

      /* Check if parent entry needs to be updated */
      mbr_changed = rtr_merge_mbr_changed(&cursor2, &father_cursor, offsets2,
                                          offsets, &new_mbr);
    }

    rec_t *orig_pred = page_copy_rec_list_start(
        merge_block, block, page_get_supremum_rec(page), index, mtr);

    if (!orig_pred) {
      goto err_exit;
    }

    btr_search_drop_page_hash_index(block);

    /* Remove the page from the level list */
    btr_level_list_remove(space, page_size, page, index, mtr);

    if (dict_index_is_spatial(index)) {
      rec_t *my_rec = father_cursor.page_cur.rec;

      page_no_t page_no = btr_node_ptr_get_child_page_no(my_rec, offsets);

      if (page_no != block->page.id.page_no()) {
        ib::fatal(UT_LOCATION_HERE, ER_IB_MSG_33)
            << "father positioned on " << page_no << " instead of "
            << block->page.id.page_no();

        ut_d(ut_error);
      }

      if (mbr_changed) {
#ifdef UNIV_DEBUG
        bool success = rtr_update_mbr_field(&cursor2, offsets2, &father_cursor,
                                            merge_page, &new_mbr, nullptr, mtr);

        ut_ad(success);
#else
        rtr_update_mbr_field(&cursor2, offsets2, &father_cursor, merge_page,
                             &new_mbr, nullptr, mtr);
#endif
      } else {
        rtr_node_ptr_delete(&father_cursor, mtr);
      }

      /* No GAP lock needs to be worrying about */
      locksys::Shard_latch_guard guard{UT_LOCATION_HERE, block->get_page_id()};
      lock_prdt_page_free_from_discard(block, lock_sys->prdt_page_hash);
      lock_rec_free_all_from_discard_page(block);
    } else {
      btr_node_ptr_delete(index, block, mtr);
      if (!dict_table_is_locking_disabled(index->table)) {
        lock_update_merge_left(merge_block, orig_pred, block);
      }
    }

    if (adjust) {
      nth_rec += page_rec_get_n_recs_before(orig_pred);
    }
  } else {
    rec_t *orig_succ;
    bool compressed;
    dberr_t err;
    btr_cur_t cursor2;
    /* father cursor pointing to node ptr
    of the right sibling */
#ifdef UNIV_BTR_DEBUG
    byte fil_page_prev[4];
#endif /* UNIV_BTR_DEBUG */

    if (dict_index_is_spatial(index)) {
      cursor2.rtr_info = nullptr;

      /* For spatial index, we disallow merge of blocks
      with different parents, since the merge would need
      to update entry (for MBR and Primary key) in the
      parent of block being merged */
      if (!rtr_check_same_block(index, &cursor2,
                                btr_cur_get_block(&father_cursor), merge_block,
                                heap)) {
        goto err_exit;
      }

      /* Set rtr_info for cursor2, since it is
      necessary in recursive page merge. */
      cursor2.rtr_info = cursor->rtr_info;
      cursor2.tree_height = cursor->tree_height;
    } else {
      btr_page_get_father(index, merge_block, mtr, &cursor2);
    }

    if (merge_page_zip && left_page_no == FIL_NULL) {
      /* The function page_zip_compress(), which will be
      invoked by page_copy_rec_list_end() below,
      requires that FIL_PAGE_PREV be FIL_NULL.
      Clear the field, but prepare to restore it. */
#ifdef UNIV_BTR_DEBUG
      memcpy(fil_page_prev, merge_page + FIL_PAGE_PREV, 4);
#endif /* UNIV_BTR_DEBUG */
      static_assert(FIL_NULL == 0xffffffff, "FIL_NULL != 0xffffffff");
      memset(merge_page + FIL_PAGE_PREV, 0xff, 4);
    }

    orig_succ = page_copy_rec_list_end(
        merge_block, block, page_get_infimum_rec(page), cursor->index, mtr);

    if (!orig_succ) {
      ut_a(merge_page_zip);
#ifdef UNIV_BTR_DEBUG
      if (left_page_no == FIL_NULL) {
        /* FIL_PAGE_PREV was restored from
        merge_page_zip. */
        ut_a(!memcmp(fil_page_prev, merge_page + FIL_PAGE_PREV, 4));
      }
#endif /* UNIV_BTR_DEBUG */
      goto err_exit;
    }

    btr_search_drop_page_hash_index(block);

#ifdef UNIV_BTR_DEBUG
    if (merge_page_zip && left_page_no == FIL_NULL) {
      /* Restore FIL_PAGE_PREV in order to avoid an assertion
      failure in btr_level_list_remove(), which will set
      the field again to FIL_NULL.  Even though this makes
      merge_page and merge_page_zip inconsistent for a
      split second, it is harmless, because the pages
      are X-latched. */
      memcpy(merge_page + FIL_PAGE_PREV, fil_page_prev, 4);
    }
#endif /* UNIV_BTR_DEBUG */

    /* Remove the page from the level list */
    btr_level_list_remove(space, page_size, page, index, mtr);

    ut_ad(btr_node_ptr_get_child_page_no(btr_cur_get_rec(&father_cursor),
                                         offsets) == block->page.id.page_no());

    /* Replace the address of the old child node (= page) with the
    address of the merge page to the right */
    btr_node_ptr_set_child_page_no(btr_cur_get_rec(&father_cursor),
                                   btr_cur_get_page_zip(&father_cursor),
                                   offsets, right_page_no, mtr);

#ifdef UNIV_DEBUG
    if (!page_is_leaf(page) && left_page_no == FIL_NULL) {
      ut_ad(REC_INFO_MIN_REC_FLAG &
            rec_get_info_bits(page_rec_get_next(page_get_infimum_rec(
                                  buf_block_get_frame(merge_block))),
                              page_is_comp(page)));
    }
#endif /* UNIV_DEBUG */

    /* For rtree, we need to update father's mbr. */
    if (dict_index_is_spatial(index)) {
      ulint *offsets2;
      ulint rec_info;

      offsets2 = rec_get_offsets(btr_cur_get_rec(&cursor2), index, nullptr,
                                 ULINT_UNDEFINED, &heap);

      ut_ad(btr_node_ptr_get_child_page_no(btr_cur_get_rec(&cursor2),
                                           offsets2) == right_page_no);

      rec_info = rec_get_info_bits(btr_cur_get_rec(&father_cursor),
                                   rec_offs_comp(offsets));
      if (rec_info & REC_INFO_MIN_REC_FLAG) {
        /* When the father node ptr is minimal rec,
        we will keep it and delete the node ptr of
        merge page. */
        rtr_merge_and_update_mbr(&father_cursor, &cursor2, offsets, offsets2,
                                 merge_page, mtr);
      } else {
        /* Otherwise, we will keep the node ptr of
        merge page and delete the father node ptr.
        This is for keeping the rec order in upper
        level. */
        rtr_merge_and_update_mbr(&cursor2, &father_cursor, offsets2, offsets,
                                 merge_page, mtr);
      }
      locksys::Shard_latch_guard guard{UT_LOCATION_HERE, block->get_page_id()};
      lock_prdt_page_free_from_discard(block, lock_sys->prdt_page_hash);
      lock_rec_free_all_from_discard_page(block);
    } else {
      compressed =
          btr_cur_pessimistic_delete(&err, true, &cursor2, BTR_CREATE_FLAG,
                                     false, 0, 0, 0, mtr, nullptr, nullptr);
      ut_a(err == DB_SUCCESS);

      if (!compressed) {
        btr_cur_compress_if_useful(&cursor2, false, mtr);
      }

      if (!dict_table_is_locking_disabled(index->table)) {
        lock_update_merge_right(merge_block, orig_succ, block);
      }
    }
  }

  if (!index->is_clustered() && !index->table->is_temporary() &&
      page_is_leaf(merge_page)) {
    /* Update the free bits of the B-tree page in the
    insert buffer bitmap.  This has to be done in a
    separate mini-transaction that is committed before the
    main mini-transaction.  We cannot update the insert
    buffer bitmap in this mini-transaction, because
    btr_compress() can be invoked recursively without
    committing the mini-transaction in between.  Since
    insert buffer bitmap pages have a lower rank than
    B-tree pages, we must not access other pages in the
    same mini-transaction after accessing an insert buffer
    bitmap page. */

    /* The free bits in the insert buffer bitmap must
    never exceed the free space on a page.  It is safe to
    decrement or reset the bits in the bitmap in a
    mini-transaction that is committed before the
    mini-transaction that affects the free space. */

    /* It is unsafe to increment the bits in a separately
    committed mini-transaction, because in crash recovery,
    the free bits could momentarily be set too high. */

    if (page_size.is_compressed()) {
      /* Because the free bits may be incremented
      and we cannot update the insert buffer bitmap
      in the same mini-transaction, the only safe
      thing we can do here is the pessimistic
      approach: reset the free bits. */
      ibuf_reset_free_bits(merge_block);
    } else {
      /* On uncompressed pages, the free bits will
      never increase here.  Thus, it is safe to
      write the bits accurately in a separate
      mini-transaction. */
      ibuf_update_free_bits_if_full(merge_block, UNIV_PAGE_SIZE,
                                    ULINT_UNDEFINED);
    }
  }

  ut_ad(page_validate(merge_page, index));
#ifdef UNIV_ZIP_DEBUG
  ut_a(!merge_page_zip || page_zip_validate(merge_page_zip, merge_page, index));
#endif /* UNIV_ZIP_DEBUG */

  if (dict_index_is_spatial(index)) {
#ifdef UNIV_GIS_DEBUG
    fprintf(stderr, "GIS_DIAG: compressed away  %ld\n",
            (long)block->page.id.page_no());
    fprintf(stderr, "GIS_DIAG: merged to %ld\n",
            (long)merge_block->page.id.page_no());
#endif

    rtr_check_discard_page(index, nullptr, block);
  }

  /* Free the file page */
  btr_page_free(index, block, mtr);

  /* btr_check_node_ptr() needs parent block latched.
  If the merge_block's parent block is not same,
  we cannot use btr_check_node_ptr() */

  ut_ad(leftmost_child || btr_check_node_ptr(index, merge_block, mtr));

func_exit:
  mem_heap_free(heap);

  if (adjust) {
    ut_ad(nth_rec > 0);
    btr_cur_position(index, page_rec_get_nth(merge_block->frame, nth_rec),
                     merge_block, cursor);
  }

  MONITOR_INC(MONITOR_INDEX_MERGE_SUCCESSFUL);

  return true;

err_exit:
  /* We play it safe and reset the free bits. */
  if (page_size.is_compressed() && merge_page && page_is_leaf(merge_page) &&
      !index->is_clustered()) {
    ibuf_reset_free_bits(merge_block);
  }

  mem_heap_free(heap);
  return false;
}

/** Discards a page that is the only page on its level.  This will empty
 the whole B-tree, leaving just an empty root page.  This function
 should never be reached, because btr_compress(), which is invoked in
 delete operations, calls btr_lift_page_up() to flatten the B-tree. */
static void btr_discard_only_page_on_level(
    dict_index_t *index, /*!< in: index tree */
    buf_block_t *block,  /*!< in: page which is the only on its level */
    mtr_t *mtr)          /*!< in: mtr */
{
  ulint page_level = 0;
  trx_id_t max_trx_id;

  /* Save the PAGE_MAX_TRX_ID from the leaf page. */
  max_trx_id = page_get_max_trx_id(buf_block_get_frame(block));

  while (block->page.id.page_no() != dict_index_get_page(index)) {
    btr_cur_t cursor;
    buf_block_t *father;
    const page_t *page = buf_block_get_frame(block);

    ut_a(page_get_n_recs(page) == 1);
    ut_a(page_level == btr_page_get_level(page));
    ut_a(btr_page_get_prev(page, mtr) == FIL_NULL);
    ut_a(btr_page_get_next(page, mtr) == FIL_NULL);

    ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));
    btr_search_drop_page_hash_index(block);

    if (dict_index_is_spatial(index)) {
      /* Check any concurrent search having this page */
      rtr_check_discard_page(index, nullptr, block);
      rtr_page_get_father(index, block, mtr, nullptr, &cursor);
    } else {
      btr_page_get_father(index, block, mtr, &cursor);
    }
    father = btr_cur_get_block(&cursor);

    if (!dict_table_is_locking_disabled(index->table)) {
      lock_update_discard(father, PAGE_HEAP_NO_SUPREMUM, block);
    }

    /* Free the file page */
    btr_page_free(index, block, mtr);

    block = father;
    page_level++;
  }

  /* block is the root page, which must be empty, except
  for the node pointer to the (now discarded) block(s). */

#ifdef UNIV_BTR_DEBUG
  if (!dict_index_is_ibuf(index)) {
    const page_t *root = buf_block_get_frame(block);
    const space_id_t space_id = dict_index_get_space(index);
    ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_LEAF + root,
                                space_id));
    ut_a(btr_root_fseg_validate(FIL_PAGE_DATA + PAGE_BTR_SEG_TOP + root,
                                space_id));
  }
#endif /* UNIV_BTR_DEBUG */

  btr_page_empty(block, buf_block_get_page_zip(block), index, 0, mtr);
  ut_ad(page_is_leaf(buf_block_get_frame(block)));

  if (!index->is_clustered() && !index->table->is_temporary()) {
    /* We play it safe and reset the free bits for the root */
    ibuf_reset_free_bits(block);

    ut_a(max_trx_id);
    page_set_max_trx_id(block, buf_block_get_page_zip(block), max_trx_id, mtr);
  }
}

/** Discards a page from a B-tree. This is used to remove the last record from
 a B-tree page: the whole page must be removed at the same time. This cannot
 be used for the root page, which is allowed to be empty. */
void btr_discard_page(btr_cur_t *cursor, /*!< in: cursor on the page to discard:
                                         not on the root page */
                      mtr_t *mtr)        /*!< in: mtr */
{
  dict_index_t *index;
  page_no_t left_page_no;
  page_no_t right_page_no;
  buf_block_t *merge_block;
  page_t *merge_page;
  buf_block_t *block;
  page_t *page;
  rec_t *node_ptr;
#ifdef UNIV_DEBUG
  btr_cur_t parent_cursor;
  bool parent_is_different = false;
#endif

  block = btr_cur_get_block(cursor);
  index = cursor->index;

  ut_ad(dict_index_get_page(index) != block->page.id.page_no());

  ut_ad(mtr_memo_contains_flagged(mtr, dict_index_get_lock(index),
                                  MTR_MEMO_X_LOCK | MTR_MEMO_SX_LOCK) ||
        index->table->is_intrinsic());

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));

  const space_id_t space = dict_index_get_space(index);

  MONITOR_INC(MONITOR_INDEX_DISCARD);

#ifdef UNIV_DEBUG
  if (dict_index_is_spatial(index)) {
    rtr_page_get_father(index, block, mtr, cursor, &parent_cursor);
  } else {
    btr_page_get_father(index, block, mtr, &parent_cursor);
  }
#endif

  /* Decide the page which will inherit the locks */

  left_page_no = btr_page_get_prev(buf_block_get_frame(block), mtr);
  right_page_no = btr_page_get_next(buf_block_get_frame(block), mtr);

  const page_size_t page_size(dict_table_page_size(index->table));

  if (left_page_no != FIL_NULL) {
    merge_block = btr_block_get(page_id_t(space, left_page_no), page_size,
                                RW_X_LATCH, UT_LOCATION_HERE, index, mtr);

    merge_page = buf_block_get_frame(merge_block);
#ifdef UNIV_BTR_DEBUG
    ut_a(btr_page_get_next(merge_page, mtr) == block->page.id.page_no());
#endif /* UNIV_BTR_DEBUG */
    ut_d(parent_is_different =
             (page_rec_get_next(page_get_infimum_rec(btr_cur_get_page(
                  &parent_cursor))) == btr_cur_get_rec(&parent_cursor)));
  } else if (right_page_no != FIL_NULL) {
    merge_block = btr_block_get(page_id_t(space, right_page_no), page_size,
                                RW_X_LATCH, UT_LOCATION_HERE, index, mtr);

    merge_page = buf_block_get_frame(merge_block);
#ifdef UNIV_BTR_DEBUG
    ut_a(btr_page_get_prev(merge_page, mtr) == block->page.id.page_no());
#endif /* UNIV_BTR_DEBUG */
    ut_d(parent_is_different = page_rec_is_supremum(
             page_rec_get_next(btr_cur_get_rec(&parent_cursor))));
  } else {
    btr_discard_only_page_on_level(index, block, mtr);

    return;
  }

  page = buf_block_get_frame(block);
  ut_a(page_is_comp(merge_page) == page_is_comp(page));
  btr_search_drop_page_hash_index(block);

  if (left_page_no == FIL_NULL && !page_is_leaf(page)) {
    /* We have to mark the leftmost node pointer on the right
    side page as the predefined minimum record */
    node_ptr = page_rec_get_next(page_get_infimum_rec(merge_page));

    ut_ad(page_rec_is_user_rec(node_ptr));

    /* This will make page_zip_validate() fail on merge_page
    until btr_level_list_remove() completes.  This is harmless,
    because everything will take place within a single
    mini-transaction and because writing to the redo log
    is an atomic operation (performed by mtr_commit()). */
    btr_set_min_rec_mark(node_ptr, mtr);
  }

  if (dict_index_is_spatial(index)) {
    btr_cur_t father_cursor;

    /* Since rtr_node_ptr_delete doesn't contain get father
    node ptr, so, we need to get father node ptr first and then
    delete it. */
    rtr_page_get_father(index, block, mtr, cursor, &father_cursor);
    rtr_node_ptr_delete(&father_cursor, mtr);
  } else {
    btr_node_ptr_delete(index, block, mtr);
  }

  /* Remove the page from the level list */
  btr_level_list_remove(space, page_size, page, index, mtr);
#ifdef UNIV_ZIP_DEBUG
  {
    page_zip_des_t *merge_page_zip = buf_block_get_page_zip(merge_block);
    ut_a(!merge_page_zip ||
         page_zip_validate(merge_page_zip, merge_page, index));
  }
#endif /* UNIV_ZIP_DEBUG */

  if (!dict_table_is_locking_disabled(index->table)) {
    if (left_page_no != FIL_NULL) {
      lock_update_discard(merge_block, PAGE_HEAP_NO_SUPREMUM, block);
    } else {
      lock_update_discard(merge_block, lock_get_min_heap_no(merge_block),
                          block);
    }
  }

  if (dict_index_is_spatial(index)) {
    rtr_check_discard_page(index, cursor, block);
  }

  /* Free the file page */
  btr_page_free(index, block, mtr);

  /* btr_check_node_ptr() needs parent block latched.
  If the merge_block's parent block is not same,
  we cannot use btr_check_node_ptr() */

  ut_ad(parent_is_different || btr_check_node_ptr(index, merge_block, mtr));
}

#ifdef UNIV_BTR_PRINT
/** Prints size info of a B-tree. */
void btr_print_size(dict_index_t *index) /*!< in: index tree */
{
  page_t *root;
  fseg_header_t *seg;
  mtr_t mtr;

  if (dict_index_is_ibuf(index)) {
    fputs(
        "Sorry, cannot print info of an ibuf tree:"
        " use ibuf functions\n",
        stderr);

    return;
  }

  mtr_start(&mtr);

  root = btr_root_get(index, &mtr);

  seg = root + PAGE_HEADER + PAGE_BTR_SEG_TOP;

  fputs("INFO OF THE NON-LEAF PAGE SEGMENT\n", stderr);
  fseg_print(seg, &mtr);

  if (!dict_index_is_ibuf(index)) {
    seg = root + PAGE_HEADER + PAGE_BTR_SEG_LEAF;

    fputs("INFO OF THE LEAF PAGE SEGMENT\n", stderr);
    fseg_print(seg, &mtr);
  }

  mtr_commit(&mtr);
}

/** Prints recursively index tree pages. */
static void btr_print_recursive(
    dict_index_t *index, /*!< in: index tree */
    buf_block_t *block,  /*!< in: index page */
    ulint width,         /*!< in: print this many entries from start
                         and end */
    mem_heap_t **heap,   /*!< in/out: heap for rec_get_offsets() */
    ulint **offsets,     /*!< in/out: buffer for rec_get_offsets() */
    mtr_t *mtr)          /*!< in: mtr */
{
  const page_t *page = buf_block_get_frame(block);
  page_cur_t cursor;
  ulint n_recs;
  ulint i = 0;
  mtr_t mtr2;

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_SX_FIX, index->table));

  ib::info(ER_IB_MSG_34) << "NODE ON LEVEL " << btr_page_get_level(page)
                         << " page " << block->page.id;

  page_print(block, index, width, width);

  n_recs = page_get_n_recs(page);

  page_cur_set_before_first(block, &cursor);
  page_cur_move_to_next(&cursor);

  while (!page_cur_is_after_last(&cursor)) {
    if (page_is_leaf(page)) {
      /* If this is the leaf level, do nothing */

    } else if ((i <= width) || (i >= n_recs - width)) {
      const rec_t *node_ptr;

      mtr_start(&mtr2);

      node_ptr = page_cur_get_rec(&cursor);

      *offsets =
          rec_get_offsets(node_ptr, index, *offsets, ULINT_UNDEFINED, heap);
      btr_print_recursive(
          index, btr_node_ptr_get_child(node_ptr, index, *offsets, &mtr2),
          width, heap, offsets, &mtr2);
      mtr_commit(&mtr2);
    }

    page_cur_move_to_next(&cursor);
    i++;
  }
}

/** Prints directories and other info of all nodes in the tree. */
void btr_print_index(dict_index_t *index, /*!< in: index */
                     ulint width) /*!< in: print this many entries from start
                                  and end */
{
  mtr_t mtr;
  buf_block_t *root;
  mem_heap_t *heap = NULL;
  ulint offsets_[REC_OFFS_NORMAL_SIZE];
  ulint *offsets = offsets_;
  rec_offs_init(offsets_);

  fputs(
      "--------------------------\n"
      "INDEX TREE PRINT\n",
      stderr);

  mtr_start(&mtr);

  root = btr_root_block_get(index, RW_SX_LATCH, &mtr);

  btr_print_recursive(index, root, width, &heap, &offsets, &mtr);
  if (heap) {
    mem_heap_free(heap);
  }

  mtr_commit(&mtr);

  ut_ad(btr_validate_index(index, 0, false));
}
#endif /* UNIV_BTR_PRINT */

#ifdef UNIV_DEBUG
bool btr_check_node_ptr(dict_index_t *index, buf_block_t *block, mtr_t *mtr) {
  mem_heap_t *heap;
  dtuple_t *tuple;
  ulint *offsets;
  btr_cur_t cursor;
  page_t *page = buf_block_get_frame(block);

  ut_ad(mtr_is_block_fix(mtr, block, MTR_MEMO_PAGE_X_FIX, index->table));

  if (dict_index_get_page(index) == block->page.id.page_no()) {
    return true;
  }

  heap = mem_heap_create(256, UT_LOCATION_HERE);

  if (dict_index_is_spatial(index)) {
    offsets = rtr_page_get_father_block(nullptr, heap, index, block, mtr,
                                        nullptr, &cursor);
  } else {
    offsets =
        btr_page_get_father_block(nullptr, heap, index, block, mtr, &cursor);
  }

  if (page_is_leaf(page)) {
    goto func_exit;
  }

  tuple = dict_index_build_node_ptr(
      index, page_rec_get_next(page_get_infimum_rec(page)), 0, heap,
      btr_page_get_level(page));

  /* For spatial index, the MBR in the parent rec could be different
  with that of first rec of child, their relationship should be
  "WITHIN" relationship */
  if (dict_index_is_spatial(index)) {
    ut_a(!cmp_dtuple_rec_with_gis(tuple, btr_cur_get_rec(&cursor), offsets,
                                  PAGE_CUR_WITHIN, index->rtr_srs.get()));
  } else {
    ut_a(!cmp_dtuple_rec(tuple, btr_cur_get_rec(&cursor), index, offsets));
  }
func_exit:
  mem_heap_free(heap);
  return true;
}
#endif /* UNIV_DEBUG */

/** Display identification information for a record. */
static void btr_index_rec_validate_report(
    const page_t *page,        /*!< in: index page */
    const rec_t *rec,          /*!< in: index record */
    const dict_index_t *index) /*!< in: index */
{
  ib::info(ER_IB_MSG_35) << "Record in index " << index->name << " of table "
                         << index->table->name << ", page "
                         << page_id_t(page_get_space_id(page),
                                      page_get_page_no(page))
                         << ", at offset " << page_offset(rec);
}

/** Checks the size and number of fields in a record based on the definition of
 the index.
 @return true if ok */
bool btr_index_rec_validate(const rec_t *rec,          /*!< in: index record */
                            const dict_index_t *index, /*!< in: index */
                            bool dump_on_error) /*!< in: true if the function
                                                 should print hex dump of
                                                 record and page on error */
{
  ulint len;
  ulint n;
  ulint i;
  const page_t *page;
  mem_heap_t *heap = nullptr;
  ulint offsets_[REC_OFFS_NORMAL_SIZE];
  ulint *offsets = offsets_;
  rec_offs_init(offsets_);

  page = page_align(rec);

  if (dict_index_is_ibuf(index)) {
    /* The insert buffer index tree can contain records from any
    other index: we cannot check the number of fields or
    their length */

    return true;
  }

#ifdef VIRTUAL_INDEX_DEBUG
  if (dict_index_has_virtual(index) || index->is_clustered()) {
    fprintf(stderr, "index name is %s\n", index->name());
  }
#endif
  if (page_is_comp(page) != dict_table_is_comp(index->table)) {
    btr_index_rec_validate_report(page, rec, index);

    ib::error(ER_IB_MSG_36)
        << "Compact flag=" << page_is_comp(page) << ", should be "
        << dict_table_is_comp(index->table);

    return false;
  }

  n = dict_index_get_n_fields(index);

  if (!page_is_comp(page) &&
      (rec_get_n_fields_old(rec, index) != n
       /* a record for older SYS_INDEXES table
       (missing merge_threshold column) is acceptable. */
       && !(index->id == DICT_INDEXES_ID &&
            rec_get_n_fields_old(rec, index) == n - 1))) {
    btr_index_rec_validate_report(page, rec, index);

    ib::error(ER_IB_MSG_37) << "Has " << rec_get_n_fields_old(rec, index)
                            << " fields, should have " << n;

    if (dump_on_error) {
      fputs("InnoDB: corrupt record ", stderr);
      rec_print_old(stderr, rec);
      putc('\n', stderr);
    }
    return false;
  }

  offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);

  for (i = 0; i < n; i++) {
    dict_field_t *field = nullptr;
    field = index->get_physical_field(i);
    const dict_col_t *col = field->col;
    ulint fixed_size = col->get_fixed_size(page_is_comp(page));

    /* nullptr for index as i is physical here */
    rec_get_nth_field_offs(nullptr, offsets, i, &len);

    /* Note that if fixed_size != 0, it equals the
    length of a fixed-size column in the clustered index,
    except the DATA_POINT, whose length would be MBR_LEN
    when it's indexed in a R-TREE. We should adjust it here.
    A prefix index of the column is of fixed, but different
    length.  When fixed_size == 0, prefix_len is the maximum
    length of the prefix index column. */

    if (col->mtype == DATA_POINT) {
      ut_ad(fixed_size == DATA_POINT_LEN);
      if (dict_index_is_spatial(index)) {
        /* For DATA_POINT data, when it has R-tree
        index, the fixed_len is the MBR of the point.
        But if it's a primary key and on R-TREE
        as the PK pointer, the length shall be
        DATA_POINT_LEN as well. */
        ut_ad((field->fixed_len == DATA_MBR_LEN && i == 0) ||
              (field->fixed_len == DATA_POINT_LEN && i != 0));
        fixed_size = field->fixed_len;
      }
    }

    if ((field->prefix_len == 0 && rec_field_not_null_not_add_col_def(len) &&
         fixed_size && len != fixed_size) ||
        (field->prefix_len > 0 && rec_field_not_null_not_add_col_def(len) &&
         len > field->prefix_len)) {
      btr_index_rec_validate_report(page, rec, index);

      ib::error error(ER_IB_MSG_1224);

      error << "Field " << i << " len is " << len << ", should be "
            << fixed_size;

      if (dump_on_error) {
        error << "; ";
        rec_print(error.m_oss, rec,
                  rec_get_info_bits(rec, rec_offs_comp(offsets)), offsets);
      }
      if (heap) {
        mem_heap_free(heap);
      }
      return false;
    }
  }

#ifdef VIRTUAL_INDEX_DEBUG
  if (dict_index_has_virtual(index) || index->is_clustered()) {
    rec_print_new(stderr, rec, offsets);
  }
#endif

  if (heap) {
    mem_heap_free(heap);
  }
  return true;
}

/** Checks the size and number of fields in records based on the definition of
 the index.
 @return true if ok */
static bool btr_index_page_validate(buf_block_t *block,  /*!< in: index page */
                                    dict_index_t *index) /*!< in: index */
{
  page_cur_t cur;
  bool ret = true;
#ifdef UNIV_DEBUG
  ulint nth = 1;
#endif /* UNIV_DEBUG */

  page_cur_set_before_first(block, &cur);

  /* Directory slot 0 should only contain the infimum record. */
  DBUG_EXECUTE_IF(
      "check_table_rec_next",
      ut_a(page_rec_get_nth_const(page_cur_get_page(&cur), 0) == cur.rec);
      ut_a(page_dir_slot_get_n_owned(
               page_dir_get_nth_slot(page_cur_get_page(&cur), 0)) == 1););

  page_cur_move_to_next(&cur);

  for (;;) {
    if (page_cur_is_after_last(&cur)) {
      break;
    }

    if (!btr_index_rec_validate(cur.rec, index, true)) {
      return false;
    }

    /* Verify that page_rec_get_nth_const() is correctly
    retrieving each record. */
    DBUG_EXECUTE_IF("check_table_rec_next",
                    ut_a(cur.rec == page_rec_get_nth_const(
                                        page_cur_get_page(&cur),
                                        page_rec_get_n_recs_before(cur.rec)));
                    ut_a(nth++ == page_rec_get_n_recs_before(cur.rec)););

    page_cur_move_to_next(&cur);
  }

  return (ret);
}

/** Report an error on one page of an index tree. */
static void btr_validate_report1(
    dict_index_t *index,      /*!< in: index */
    ulint level,              /*!< in: B-tree level */
    const buf_block_t *block) /*!< in: index page */
{
  ib::error error(ER_IB_MSG_1225);
  error << "In page " << block->page.id.page_no() << " of index " << index->name
        << " of table " << index->table->name;

  if (level > 0) {
    error << ", index tree level " << level;
  }
}

/** Report an error on two pages of an index tree. */
static void btr_validate_report2(
    const dict_index_t *index, /*!< in: index */
    ulint level,               /*!< in: B-tree level */
    const buf_block_t *block1, /*!< in: first index page */
    const buf_block_t *block2) /*!< in: second index page */
{
  ib::error error(ER_IB_MSG_1226);
  error << "In pages " << block1->page.id << " and " << block2->page.id
        << " of index " << index->name << " of table " << index->table->name;

  if (level > 0) {
    error << ", index tree level " << level;
  }
}

/** Validates index tree level.
 @return true if ok */
static bool btr_validate_level(
    dict_index_t *index, /*!< in: index tree */
    const trx_t *trx,    /*!< in: transaction or NULL */
    ulint level,         /*!< in: level number */
    bool lockout)        /*!< in: true if X-latch index is intended */
{
  buf_block_t *block;
  page_t *page;
  buf_block_t *right_block = nullptr; /* remove warning */
  page_t *right_page = nullptr;       /* remove warning */
  page_t *father_page;
  btr_cur_t node_cur;
  btr_cur_t right_node_cur;
  rec_t *rec;
  page_no_t right_page_no;
  page_no_t left_page_no;
  page_cur_t cursor;
  dtuple_t *node_ptr_tuple;
  bool ret = true;
  mtr_t mtr;
  mem_heap_t *heap = mem_heap_create(256, UT_LOCATION_HERE);
  fseg_header_t *seg;
  ulint *offsets = nullptr;
  ulint *offsets2 = nullptr;
#ifdef UNIV_ZIP_DEBUG
  page_zip_des_t *page_zip;
#endif /* UNIV_ZIP_DEBUG */
  ulint savepoint = 0;
  ulint savepoint2 = 0;
  page_no_t parent_page_no = FIL_NULL;
  page_no_t parent_right_page_no = FIL_NULL;
  bool rightmost_child = false;

  mtr_start(&mtr);

  if (!srv_read_only_mode) {
    if (lockout) {
      mtr_x_lock(dict_index_get_lock(index), &mtr, UT_LOCATION_HERE);
    } else {
      mtr_sx_lock(dict_index_get_lock(index), &mtr, UT_LOCATION_HERE);
    }
  }

  block = btr_root_block_get(index, RW_SX_LATCH, &mtr);
  page = buf_block_get_frame(block);
  seg = page + PAGE_HEADER + PAGE_BTR_SEG_TOP;

#ifdef UNIV_RTR_DEBUG
  if (dict_index_is_spatial(index)) {
    fprintf(stderr, "Root page no: %lu\n", (ulong)page_get_page_no(page));
  }
#endif

  const fil_space_t *space = fil_space_get(index->space);
  const page_size_t table_page_size(dict_table_page_size(index->table));
  const page_size_t space_page_size(space->flags);

  if (!table_page_size.equals_to(space_page_size)) {
    ib::warn(ER_IB_MSG_38) << "Flags mismatch: table=" << index->table->flags
                           << ", tablespace=" << space->flags;

    mtr_commit(&mtr);

    return (false);
  }

  while (level != btr_page_get_level(page)) {
    const rec_t *node_ptr;

    if (fseg_page_is_free(seg, block->page.id.space(),
                          block->page.id.page_no())) {
      btr_validate_report1(index, level, block);

      ib::warn(ER_IB_MSG_39) << "Page is free";

      ret = false;
    }

    ut_a(index->space == block->page.id.space());
    ut_a(index->space == page_get_space_id(page));
#ifdef UNIV_ZIP_DEBUG
    page_zip = buf_block_get_page_zip(block);
    ut_a(!page_zip || page_zip_validate(page_zip, page, index));
#endif /* UNIV_ZIP_DEBUG */
    ut_a(!page_is_leaf(page));

    page_cur_set_before_first(block, &cursor);
    page_cur_move_to_next(&cursor);

    node_ptr = page_cur_get_rec(&cursor);
    offsets = rec_get_offsets(node_ptr, index, offsets, ULINT_UNDEFINED, &heap);

    savepoint2 = mtr_set_savepoint(&mtr);
    block = btr_node_ptr_get_child(node_ptr, index, offsets, &mtr);
    page = buf_block_get_frame(block);

    /* For R-Tree, since record order might not be the same as
    linked index page in the lower level, we need to travers
    backwards to get the first page rec in this level.
    This is only used for index validation. Spatial index
    does not use such scan for any of its DML or query
    operations  */
    if (dict_index_is_spatial(index)) {
      left_page_no = btr_page_get_prev(page, &mtr);

      while (left_page_no != FIL_NULL) {
        page_id_t left_page_id(index->space, left_page_no);
        /* To obey latch order of tree blocks,
        we should release the right_block once to
        obtain lock of the uncle block. */
        mtr_release_block_at_savepoint(&mtr, savepoint2, block);

        savepoint2 = mtr_set_savepoint(&mtr);
        block = btr_block_get(left_page_id, table_page_size, RW_SX_LATCH,
                              UT_LOCATION_HERE, index, &mtr);
        page = buf_block_get_frame(block);
        left_page_no = btr_page_get_prev(page, &mtr);
      }
    }
  }

  /* Now we are on the desired level. Loop through the pages on that
  level. */

  if (level == 0) {
    /* Leaf pages are managed in their own file segment. */
    seg -= PAGE_BTR_SEG_TOP - PAGE_BTR_SEG_LEAF;
  }

loop:
  mem_heap_empty(heap);
  offsets = offsets2 = nullptr;
  if (!srv_read_only_mode) {
    if (lockout) {
      mtr_x_lock(dict_index_get_lock(index), &mtr, UT_LOCATION_HERE);
    } else {
      mtr_sx_lock(dict_index_get_lock(index), &mtr, UT_LOCATION_HERE);
    }
  }

#ifdef UNIV_ZIP_DEBUG
  page_zip = buf_block_get_page_zip(block);
  ut_a(!page_zip || page_zip_validate(page_zip, page, index));
#endif /* UNIV_ZIP_DEBUG */

  ut_a(block->page.id.space() == index->space);

  if (fseg_page_is_free(seg, block->page.id.space(),
                        block->page.id.page_no())) {
    btr_validate_report1(index, level, block);

    ib::warn(ER_IB_MSG_40) << "Page is marked as free";
    ret = false;

  } else if (btr_page_get_index_id(page) != index->id) {
    ib::error(ER_IB_MSG_41) << "Page index id " << btr_page_get_index_id(page)
                            << " != data dictionary index id " << index->id;

    ret = false;

  } else if (!page_validate(page, index)) {
    btr_validate_report1(index, level, block);
    ret = false;

  } else if (level == 0 && !btr_index_page_validate(block, index)) {
    /* We are on level 0. Check that the records have the right
    number of fields, and field lengths are right. */

    ret = false;
  }

  ut_a(btr_page_get_level(page) == level);

  right_page_no = btr_page_get_next(page, &mtr);
  left_page_no = btr_page_get_prev(page, &mtr);

  ut_a(!page_is_empty(page) ||
       (level == 0 && page_get_page_no(page) == dict_index_get_page(index)));

  if (right_page_no != FIL_NULL) {
    const rec_t *right_rec;
    savepoint = mtr_set_savepoint(&mtr);

    right_block =
        btr_block_get(page_id_t(index->space, right_page_no), table_page_size,
                      RW_SX_LATCH, UT_LOCATION_HERE, index, &mtr);

    right_page = buf_block_get_frame(right_block);

    if (btr_page_get_prev(right_page, &mtr) != page_get_page_no(page)) {
      btr_validate_report2(index, level, block, right_block);
      fputs(
          "InnoDB: broken FIL_PAGE_NEXT"
          " or FIL_PAGE_PREV links\n",
          stderr);

      ret = false;
    }

    if (page_is_comp(right_page) != page_is_comp(page)) {
      btr_validate_report2(index, level, block, right_block);
      fputs("InnoDB: 'compact' flag mismatch\n", stderr);

      ret = false;

      goto node_ptr_fails;
    }

    rec = page_rec_get_prev(page_get_supremum_rec(page));
    right_rec = page_rec_get_next(page_get_infimum_rec(right_page));
    offsets = rec_get_offsets(rec, index, offsets, ULINT_UNDEFINED, &heap);
    offsets2 =
        rec_get_offsets(right_rec, index, offsets2, ULINT_UNDEFINED, &heap);

    /* For spatial index, we cannot guarantee the key ordering
    across pages, so skip the record compare verification for
    now. Will enhanced in special R-Tree index validation scheme */
    if (!dict_index_is_spatial(index) &&
        cmp_rec_rec(rec, right_rec, offsets, offsets2, index, false) >= 0) {
      btr_validate_report2(index, level, block, right_block);

      fputs(
          "InnoDB: records in wrong order"
          " on adjacent pages\n",
          stderr);

      fputs("InnoDB: record ", stderr);
      rec = page_rec_get_prev(page_get_supremum_rec(page));
      rec_print(stderr, rec, index);
      putc('\n', stderr);
      fputs("InnoDB: record ", stderr);
      rec = page_rec_get_next(page_get_infimum_rec(right_page));
      rec_print(stderr, rec, index);
      putc('\n', stderr);

      ret = false;
    }
  }

  if (level > 0 && left_page_no == FIL_NULL) {
    ut_a(REC_INFO_MIN_REC_FLAG &
         rec_get_info_bits(page_rec_get_next(page_get_infimum_rec(page)),
                           page_is_comp(page)));
  }

  /* Similarly skip the father node check for spatial index for now,
  for a couple of reasons:
  1) As mentioned, there is no ordering relationship between records
  in parent level and linked pages in the child level.
  2) Search parent from root is very costly for R-tree.
  We will add special validation mechanism for R-tree later (WL #7520) */
  if (!dict_index_is_spatial(index) &&
      block->page.id.page_no() != dict_index_get_page(index)) {
    /* Check father node pointers */
    rec_t *node_ptr;

    btr_cur_position(index, page_rec_get_next(page_get_infimum_rec(page)),
                     block, &node_cur);
    offsets = btr_page_get_father_node_ptr_for_validate(
        offsets, heap, &node_cur, UT_LOCATION_HERE, &mtr);

    father_page = btr_cur_get_page(&node_cur);
    node_ptr = btr_cur_get_rec(&node_cur);

    parent_page_no = page_get_page_no(father_page);
    parent_right_page_no = btr_page_get_next(father_page, &mtr);
    rightmost_child = page_rec_is_supremum(page_rec_get_next(node_ptr));

    btr_cur_position(index, page_rec_get_prev(page_get_supremum_rec(page)),
                     block, &node_cur);

    offsets = btr_page_get_father_node_ptr_for_validate(
        offsets, heap, &node_cur, UT_LOCATION_HERE, &mtr);

    if (node_ptr != btr_cur_get_rec(&node_cur) ||
        btr_node_ptr_get_child_page_no(node_ptr, offsets) !=
            block->page.id.page_no()) {
      btr_validate_report1(index, level, block);

      fputs("InnoDB: node pointer to the page is wrong\n", stderr);

      fputs("InnoDB: node ptr ", stderr);
      rec_print(stderr, node_ptr, index);

      rec = btr_cur_get_rec(&node_cur);
      fprintf(stderr,
              "\n"
              "InnoDB: node ptr child page n:o %lu\n",
              (ulong)btr_node_ptr_get_child_page_no(rec, offsets));

      fputs("InnoDB: record on page ", stderr);
      rec_print_new(stderr, rec, offsets);
      putc('\n', stderr);
      ret = false;

      goto node_ptr_fails;
    }

    if (!page_is_leaf(page)) {
      node_ptr_tuple = dict_index_build_node_ptr(
          index, page_rec_get_next(page_get_infimum_rec(page)), 0, heap,
          btr_page_get_level(page));

      if (cmp_dtuple_rec(node_ptr_tuple, node_ptr, index, offsets)) {
        const rec_t *first_rec = page_rec_get_next(page_get_infimum_rec(page));

        btr_validate_report1(index, level, block);

        ib::error(ER_IB_MSG_42) << "Node ptrs differ on levels > 0";

        fputs("InnoDB: node ptr ", stderr);
        rec_print_new(stderr, node_ptr, offsets);
        fputs("InnoDB: first rec ", stderr);
        rec_print(stderr, first_rec, index);
        putc('\n', stderr);
        ret = false;

        goto node_ptr_fails;
      }
    }

    if (left_page_no == FIL_NULL) {
      ut_a(node_ptr == page_rec_get_next(page_get_infimum_rec(father_page)));
      ut_a(btr_page_get_prev(father_page, &mtr) == FIL_NULL);
    }

    if (right_page_no == FIL_NULL) {
      ut_a(node_ptr == page_rec_get_prev(page_get_supremum_rec(father_page)));
      ut_a(btr_page_get_next(father_page, &mtr) == FIL_NULL);
    } else {
      const rec_t *right_node_ptr;

      right_node_ptr = page_rec_get_next(node_ptr);

      if (!lockout && rightmost_child) {
        /* To obey latch order of tree blocks,
        we should release the right_block once to
        obtain lock of the uncle block. */
        mtr_release_block_at_savepoint(&mtr, savepoint, right_block);

        btr_block_get(page_id_t(index->space, parent_right_page_no),
                      table_page_size, RW_SX_LATCH, UT_LOCATION_HERE, index,
                      &mtr);

        right_block = btr_block_get(page_id_t(index->space, right_page_no),
                                    table_page_size, RW_SX_LATCH,
                                    UT_LOCATION_HERE, index, &mtr);
      }

      btr_cur_position(index,
                       page_rec_get_next(page_get_infimum_rec(
                           buf_block_get_frame(right_block))),
                       right_block, &right_node_cur);

      offsets = btr_page_get_father_node_ptr_for_validate(
          offsets, heap, &right_node_cur, UT_LOCATION_HERE, &mtr);

      if (right_node_ptr != page_get_supremum_rec(father_page)) {
        if (btr_cur_get_rec(&right_node_cur) != right_node_ptr) {
          ret = false;
          fputs(
              "InnoDB: node pointer to"
              " the right page is wrong\n",
              stderr);

          btr_validate_report1(index, level, block);
        }
      } else {
        page_t *right_father_page = btr_cur_get_page(&right_node_cur);

        if (btr_cur_get_rec(&right_node_cur) !=
            page_rec_get_next(page_get_infimum_rec(right_father_page))) {
          ret = false;
          fputs(
              "InnoDB: node pointer 2 to"
              " the right page is wrong\n",
              stderr);

          btr_validate_report1(index, level, block);
        }

        if (page_get_page_no(right_father_page) !=
            btr_page_get_next(father_page, &mtr)) {
          ret = false;
          fputs(
              "InnoDB: node pointer 3 to"
              " the right page is wrong\n",
              stderr);

          btr_validate_report1(index, level, block);
        }
      }
    }
  }

node_ptr_fails:
  /* Commit the mini-transaction to release the latch on 'page'.
  Re-acquire the latch on right_page, which will become 'page'
  on the next loop.  The page has already been checked. */
  mtr_commit(&mtr);

  if (trx_is_interrupted(trx)) {
    /* On interrupt, return the current status. */
  } else if (right_page_no != FIL_NULL) {
    mtr_start(&mtr);

    if (!lockout) {
      if (rightmost_child) {
        if (parent_right_page_no != FIL_NULL) {
          btr_block_get(page_id_t(index->space, parent_right_page_no),
                        table_page_size, RW_SX_LATCH, UT_LOCATION_HERE, index,
                        &mtr);
        }
      } else if (parent_page_no != FIL_NULL) {
        btr_block_get(page_id_t(index->space, parent_page_no), table_page_size,
                      RW_SX_LATCH, UT_LOCATION_HERE, index, &mtr);
      }
    }

    block =
        btr_block_get(page_id_t(index->space, right_page_no), table_page_size,
                      RW_SX_LATCH, UT_LOCATION_HERE, index, &mtr);

    page = buf_block_get_frame(block);

    goto loop;
  }

  mem_heap_free(heap);

  return (ret);
}

/** Do an index level validation of spaital index tree.
 @return        true if no error found */
static bool btr_validate_spatial_index(
    dict_index_t *index, /*!< in: index */
    const trx_t *trx)    /*!< in: transaction or NULL */
{
  mtr_t mtr;
  bool ok = true;

  mtr_start(&mtr);

  mtr_x_lock(dict_index_get_lock(index), &mtr, UT_LOCATION_HERE);

  page_t *root = btr_root_get(index, &mtr);
  ulint n = btr_page_get_level(root);

#ifdef UNIV_RTR_DEBUG
  fprintf(stderr, "R-tree level is %lu\n", n);
#endif /* UNIV_RTR_DEBUG */

  for (ulint i = 0; i <= n; ++i) {
#ifdef UNIV_RTR_DEBUG
    fprintf(stderr, "Level %lu:\n", n - i);
#endif /* UNIV_RTR_DEBUG */

    if (!btr_validate_level(index, trx, n - i, true)) {
      ok = false;
      break;
    }
  }

  mtr_commit(&mtr);

  return (ok);
}

/** Checks the consistency of an index tree.
 @return true if ok */
bool btr_validate_index(
    dict_index_t *index, /*!< in: index */
    const trx_t *trx,    /*!< in: transaction or NULL */
    bool lockout)        /*!< in: true if X-latch index is intended */
{
  /* Full Text index are implemented by auxiliary tables,
  not the B-tree */
  if (dict_index_is_online_ddl(index) || (index->type & DICT_FTS)) {
    return (true);
  }

  if (dict_index_is_spatial(index)) {
    return (btr_validate_spatial_index(index, trx));
  }

  mtr_t mtr;

#ifdef UNIV_DEBUG
  /* Check the FSEG_NOT_FULL_N_USED field stored in the segment inode. */
  {
    const space_id_t space_id = dict_index_get_space(index);

    fil_space_t *space = fil_space_acquire(space_id);

    if (space == nullptr) {
      return true;
    }

    mtr_start(&mtr);
    const page_t *const root = btr_root_get(index, &mtr);
    mtr_x_lock(&space->latch, &mtr, UT_LOCATION_HERE);
    const page_size_t page_size = dict_table_page_size(index->table);

    for (auto offset : {PAGE_BTR_SEG_LEAF, PAGE_BTR_SEG_TOP}) {
      const fseg_header_t *const seg_header = root + PAGE_HEADER + offset;
      fseg_inode_t *inode =
          fseg_inode_get(seg_header, space_id, page_size, &mtr);
      File_segment_inode fsi(space_id, page_size, inode, &mtr);
      ut_ad(fsi.verify_not_full_n_used());
    }

    mtr_commit(&mtr);

    fil_space_release(space);
  }
#endif /* UNIV_DEBUG */

  mtr_start(&mtr);

  if (!srv_read_only_mode) {
    if (lockout) {
      mtr_x_lock(dict_index_get_lock(index), &mtr, UT_LOCATION_HERE);
    } else {
      mtr_sx_lock(dict_index_get_lock(index), &mtr, UT_LOCATION_HERE);
    }
  }

  bool ok = true;
  page_t *root = btr_root_get(index, &mtr);
  ulint n = btr_page_get_level(root);

  for (ulint i = 0; i <= n; ++i) {
    if (!btr_validate_level(index, trx, n - i, lockout)) {
      ok = false;
      break;
    }
  }

  mtr_commit(&mtr);

  return (ok);
}

/** Checks if the page in the cursor can be merged with given page.
 If necessary, re-organize the merge_page.
 @return        true if possible to merge. */
static bool btr_can_merge_with_page(
    btr_cur_t *cursor,         /*!< in: cursor on the page to merge */
    page_no_t page_no,         /*!< in: a sibling page */
    buf_block_t **merge_block, /*!< out: the merge block */
    mtr_t *mtr)                /*!< in: mini-transaction */
{
  dict_index_t *index;
  page_t *page;
  ulint n_recs;
  ulint data_size;
  ulint max_ins_size_reorg;
  ulint max_ins_size;
  buf_block_t *mblock;
  page_t *mpage;
  DBUG_TRACE;

  if (page_no == FIL_NULL) {
    *merge_block = nullptr;
    return false;
  }

  index = cursor->index;
  page = btr_cur_get_page(cursor);

  const page_id_t page_id(dict_index_get_space(index), page_no);
  const page_size_t page_size(dict_table_page_size(index->table));

  mblock = btr_block_get(page_id, page_size, RW_X_LATCH, UT_LOCATION_HERE,
                         index, mtr);
  mpage = buf_block_get_frame(mblock);

  n_recs = page_get_n_recs(page);
  data_size = page_get_data_size(page);

  max_ins_size_reorg = page_get_max_insert_size_after_reorganize(mpage, n_recs);

  if (data_size > max_ins_size_reorg) {
    goto error;
  }

  /* If compression padding tells us that merging will result in
  too packed up page i.e.: which is likely to cause compression
  failure then don't merge the pages. */
  if (page_size.is_compressed() && page_is_leaf(mpage) &&
      (page_get_data_size(mpage) + data_size >=
       dict_index_zip_pad_optimal_page_size(index))) {
    goto error;
  }

  max_ins_size = page_get_max_insert_size(mpage, n_recs);

  if (data_size > max_ins_size) {
    /* We have to reorganize mpage */

    if (!btr_page_reorganize_block(false, page_zip_level, mblock, index, mtr)) {
      goto error;
    }

    max_ins_size = page_get_max_insert_size(mpage, n_recs);

    ut_ad(page_validate(mpage, index));
    ut_ad(max_ins_size == max_ins_size_reorg);

    if (data_size > max_ins_size) {
      /* Add fault tolerance, though this should
      never happen */

      goto error;
    }
  }

  *merge_block = mblock;
  return true;

error:
  *merge_block = nullptr;
  return false;
}

/** Create an SDI Index
@param[in]      space_id        Tablespace id
@param[in,out]  mtr             Mini-transaction
@param[in,out]  table           SDI table
@return root page number of the SDI index created or FIL_NULL on failure */
static page_no_t btr_sdi_create(space_id_t space_id, mtr_t *mtr,
                                dict_table_t *table) {
  dict_index_t *index = table->first_index();
  ut_ad(index != nullptr);
  ut_ad(UT_LIST_GET_LEN(table->indexes) == 1);

  index->page = btr_create(DICT_CLUSTERED | DICT_UNIQUE | DICT_SDI, space_id,
                           index->id, index, mtr);

  return (index->page);
}

/** Creates SDI index and stores the root page numbers in page 1 & 2
@param[in]      space_id        tablespace id
@param[in]      dict_locked     true if dict_sys mutex is acquired
@return DB_SUCCESS on success, else DB_ERROR on failure */
dberr_t btr_sdi_create_index(space_id_t space_id, bool dict_locked) {
  fil_space_t *space = fil_space_acquire(space_id);
  if (space == nullptr) {
    ut_d(ut_error);
    ut_o(return (DB_ERROR));
  }

  dict_table_t *sdi_table;
  page_no_t sdi_root_page_num;

  sdi_table = dict_sdi_get_table(space_id, dict_locked, true);
  ut_ad(sdi_table != nullptr);

  mtr_t mtr;
  mtr.start();

  const page_size_t page_size = page_size_t(space->flags);

  /* Create B-Tree root page for SDI Indexes */

  sdi_root_page_num = btr_sdi_create(space_id, &mtr, sdi_table);

  if (sdi_root_page_num == FIL_NULL) {
    ib::error(ER_IB_MSG_43) << "Unable to create root index page"
                               " for SDI table "
                            << " in tablespace " << space_id;
    mtr.commit();
    dict_sdi_remove_from_cache(space_id, sdi_table, dict_locked);
    fil_space_release(space);
    return (DB_ERROR);
  } else {
    dict_index_t *index = sdi_table->first_index();
    index->page = sdi_root_page_num;
  }

  buf_block_t *block = buf_page_get(page_id_t(space_id, 0), page_size,
                                    RW_SX_LATCH, UT_LOCATION_HERE, &mtr);

  buf_block_dbg_add_level(block, SYNC_FSP_PAGE);

  page_t *page = buf_block_get_frame(block);

  /* Write SDI Index root page numbers to Page 0 */
  fsp_sdi_write_root_to_page(page, page_size, sdi_root_page_num, &mtr);

  /* Space flags from memory */
  uint32_t fsp_flags = space->flags;

  ut_ad(fsp_header_get_field(page, FSP_SPACE_FLAGS) == fsp_flags);

  fsp_flags_set_sdi(fsp_flags);
  mlog_write_ulint(FSP_HEADER_OFFSET + FSP_SPACE_FLAGS + page, fsp_flags,
                   MLOG_4BYTES, &mtr);

  mtr.commit();

  fil_space_set_flags(space, fsp_flags);

  dict_table_close(sdi_table, dict_locked, false);

  fil_space_release(space);
  return (DB_SUCCESS);
}
#endif /* !UNIV_HOTBACKUP */
