Hi, all. I want to report a bug about the recovery of two-phase transaction, in current implementation of crash recovery, there are two ways to recover 2pc data: 1、before redo, func restoreTwoPhaseData() will restore 2pc data those xid < ShmemVariableCache->nextXid, which is initialized from checkPoint.nextXid; 2、during redo, func xact_redo() will add 2pc from wal; The following scenario may cause the same 2pc transaction to be added repeatedly, I have attached a patch for pg11 that reproduces the error: 1、start creating checkpoint_1, checkpoint_1.redo is set as curInsert; 2、before set checkPoint_1.nextXid, a new 2pc is prepared, suppose the xid of this 2pc is 100, and then ShmemVariableCache->nextXid will be advanced as 101; 3、checkPoint_1.nextXid is set as 101; 4、in CheckPointTwoPhase() of checkpoint_1, 2pc_100 won't be copied to disk because its prepare_end_lsn > checkpoint_1.redo; 5、checkPoint_1 is finished, after checkpoint_timeout, start creating checkpoint_2; 6、during checkpoint_2, data of 2pc_100 will be copied to disk; 7、before UpdateControlFile() of checkpoint_2, crash happened; 8、during crash recovery, redo will start from checkpoint_1, and 2pc_100 will be restored first by restoreTwoPhaseData() because xid_100 < checkPoint_1.nextXid, which is 101; 9、because prepare_start_lsn of 2pc_100 > checkpoint_1.redo, 2pc_100 will be added again by xact_redo() during wal replay, resulting in the same 2pc data being added twice; 10、In RecoverPreparedTransactions() -> lock_twophase_recover(), lock the same 2pc will cause FATAL. After running the patch that reproduced the error, you will get the following error during crash recovery: 2023-07-10 13:04:30.670 UTC [11169] LOG: recovering prepared transaction 569 from shared memory 2023-07-10 13:04:30.670 UTC [11169] LOG: recovering prepared transaction 569 from shared memory 2023-07-10 13:04:30.670 UTC [11169] FATAL: lock ExclusiveLock on object 569/0/0 is already held 2023-07-10 13:04:30.670 UTC [11168] LOG: startup process (PID 11169) exited with exit code 1 2023-07-10 13:04:30.670 UTC [11168] LOG: aborting startup due to startup process failure I also added a patch for pg11 to fix this problem, hope you can check it when you have time. Thanks & Best Regard
0001-Reproduce-the-error-in-lock_twophase_recover_11.patch
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