The file_fdw module provides the foreign-data wrapper
  file_fdw, which can be used to access data
  files in the server's file system, or to execute programs on the server
  and read their output.  The data file or program output must be in a format
  that can be read by COPY FROM;
  see COPY for details.
  Access to data files is currently read-only.
 
A foreign table created using this wrapper can have the following options:
filename
     Specifies the file to be read.  Must be an absolute path name.
     Either filename or program must be
     specified, but not both.
    
program
     Specifies the command to be executed.  The standard output of this
     command will be read as though COPY FROM PROGRAM were used.
     Either program or filename must be
     specified, but not both.
    
format
     Specifies the data format,
     the same as COPY's FORMAT option.
    
header
     Specifies whether the data has a header line,
     the same as COPY's HEADER option.
    
delimiter
     Specifies the data delimiter character,
     the same as COPY's DELIMITER option.
    
quote
     Specifies the data quote character,
     the same as COPY's QUOTE option.
    
escape
     Specifies the data escape character,
     the same as COPY's ESCAPE option.
    
null
     Specifies the data null string,
     the same as COPY's NULL option.
    
encoding
     Specifies the data encoding,
     the same as COPY's ENCODING option.
    
  Note that while COPY allows options such as HEADER
  to be specified without a corresponding value, the foreign table option
  syntax requires a value to be present in all cases.  To activate
  COPY options typically written without a value, you can pass
  the value TRUE, since all such options are Booleans.
 
A column of a foreign table created using this wrapper can have the following options:
force_not_null
     This is a Boolean option.  If true, it specifies that values of the
     column should not be matched against the null string (that is, the
     table-level null option).  This has the same effect
     as listing the column in COPY's
     FORCE_NOT_NULL option.
    
force_null
     This is a Boolean option.  If true, it specifies that values of the
     column which match the null string are returned as NULL
     even if the value is quoted. Without this option, only unquoted
     values matching the null string are returned as NULL.
     This has the same effect  as listing the column in
     COPY's FORCE_NULL option.
    
  COPY's OIDS and
  FORCE_QUOTE options are currently not supported by
  file_fdw.
 
  These options can only be specified for a foreign table or its columns, not
  in the options of the file_fdw foreign-data wrapper, nor in the
  options of a server or user mapping using the wrapper.
 
  Changing table-level options requires being a superuser or having the privileges
  of the default role pg_read_server_files (to use a filename) or
  the default role pg_execute_server_programs (to use a program),
  for security reasons: only certain users should be able to control which file is
  read or which program is run.  In principle regular users could be allowed to
  change the other options, but that's not supported at present.
 
  When specifying the program option, keep in mind that the option
  string is executed by the shell.  If you need to pass any arguments to the
  command that come from an untrusted source, you must be careful to strip or
  escape any characters that might have special meaning to the shell.
  For security reasons, it is best to use a fixed command string, or at least
  avoid passing any user input in it.
 
  For a foreign table using file_fdw, EXPLAIN shows
  the name of the file to be read or program to be run.
  For a file, unless COSTS OFF is
  specified, the file size (in bytes) is shown as well.
 
Example F.1. Create a Foreign Table for PostgreSQL CSV Logs
   One of the obvious uses for file_fdw is to make
   the PostgreSQL activity log available as a table for querying.  To
   do this, first you must be logging to a CSV file, which here we
   will call pglog.csv.  First, install file_fdw
   as an extension:
  
CREATE EXTENSION file_fdw;
Then create a foreign server:
CREATE SERVER pglog FOREIGN DATA WRAPPER file_fdw;
   Now you are ready to create the foreign data table.  Using the
   CREATE FOREIGN TABLE command, you will need to define
   the columns for the table, the CSV file name, and its format:
CREATE FOREIGN TABLE pglog ( log_time timestamp(3) with time zone, user_name text, database_name text, process_id integer, connection_from text, session_id text, session_line_num bigint, command_tag text, session_start_time timestamp with time zone, virtual_transaction_id text, transaction_id bigint, error_severity text, sql_state_code text, message text, detail text, hint text, internal_query text, internal_query_pos integer, context text, query text, query_pos integer, location text, application_name text ) SERVER pglog OPTIONS ( filename '/home/josh/data/log/pglog.csv', format 'csv' );
That's it — now you can query your log directly. In production, of course, you would need to define some way to deal with log rotation.