Show GIDs of two-phase commit commands as constants in pg_stat_statements
This relies on the "location" field added to TransactionStmt in
31de7e6,
now applied to the "gid" field used by 2PC commands. These commands are
now reported like:
COMMIT PREPARED 1ドル
PREPARE TRANSACTION 1ドル
ROLLBACK PREPARED 1ドル
Applying constants for these commands is a huge advantage for workloads
that rely a lot on 2PC commands with different GIDs. Some tests are
added to track the new behavior.
Reviewed-by: Julien Rouhaud
Discussion: https://postgr.es/m/ZMhT9kNtJJsHw6jK@paquier.xyz