ROLLBACK PREPARED — cancel a transaction that was earlier prepared for two-phase commit
ROLLBACK PREPARED transaction_id   ROLLBACK PREPARED rolls back a transaction that is in
   prepared state.
  
transaction_idThe transaction identifier of the transaction that is to be rolled back.
To roll back a prepared transaction, you must be either the same user that executed the transaction originally, or a superuser. But you do not have to be in the same session that executed the transaction.
This command cannot be executed inside a transaction block. The prepared transaction is rolled back immediately.
   All currently available prepared transactions are listed in the
   pg_prepared_xacts
   system view.
  
   Roll back the transaction identified by the transaction
   identifier foobar:
ROLLBACK PREPARED 'foobar';
   ROLLBACK PREPARED is a
   PostgreSQL extension.  It is intended for use by
   external transaction management systems, some of which are covered by
   standards (such as X/Open XA), but the SQL side of those systems is not
   standardized.