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When a corrupted two-phase state file is found by WAL replay, be it for crash recovery or archive recovery, then the file is simply skipped and a WARNING is logged to the user, causing the transaction to be silently lost. Facing an on-disk WAL file which is corrupted is as likely to happen as what is stored in WAL records, but WAL records are already able to fail hard if there is a CRC mismatch. On-disk two-phase state files, on the contrary, are simply ignored if corrupted. Note that when restoring the initial two-phase data state at recovery, files newer than the horizon XID are discarded hence no files present in pg_twophase/ should be torned and have been made durable by a previous checkpoint, so recovery should never see any corrupted two-phase state file by design. The situation got better since 978b2f6 which has added two-phase state information directly in WAL instead of using on-disk files, so the risk is limited to two-phase transactions which live across at least one checkpoint for long periods. Backups having legit two-phase state files on-disk could also lose silently transactions when restored if things get corrupted. This behavior exists since two-phase commit has been introduced, no back-patch is done for now per the lack of complaints about this problem. Author: Michael Paquier Discussion: https://postgr.es/m/20180709050309.GM1467@paquier.xyz