Assertion failure with epoch when replaying standby records for 2PC

Hi all,

rorqual has failed today with a very interesting failure:
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=rorqual&dt=2024-01-17%2005%3A06%3A31

This has caused an assertion failure for a 2PC transaction when
replaying one of the tests from the main regression suite:
2024-01-17 05:08:23.143 UTC [3242608] DETAIL:  Last completed transaction was at log time 2024-01-17
05:08:22.920244+00.
TRAP: failed Assert("epoch > 0"), File: "../pgsql/src/backend/access/transam/twophase.c", Line: 969, PID: 3242610
postgres: standby_1: startup recovering 00000001000000000000000C(ExceptionalCondition+0x83)[0x55746c7838c1]
postgres: standby_1: startup recovering 00000001000000000000000C(+0x194f0e)[0x55746c371f0e]
postgres: standby_1: startup recovering 00000001000000000000000C(StandbyTransactionIdIsPrepared+0x29)[0x55746c373120]
postgres: standby_1: startup recovering 00000001000000000000000C(StandbyReleaseOldLocks+0x3f)[0x55746c621357]
postgres: standby_1: startup recovering 00000001000000000000000C(ProcArrayApplyRecoveryInfo+0x50)[0x55746c61bbb5]
postgres: standby_1: startup recovering 00000001000000000000000C(standby_redo+0xe1)[0x55746c621490]
postgres: standby_1: startup recovering 00000001000000000000000C(PerformWalRecovery+0xa5e)[0x55746c392404]
postgres: standby_1: startup recovering 00000001000000000000000C(StartupXLOG+0x3ac)[0x55746c3862b8]
postgres: standby_1: startup recovering 00000001000000000000000C(StartupProcessMain+0xd9)[0x55746c5a60f6]
postgres: standby_1: startup recovering 00000001000000000000000C(AuxiliaryProcessMain+0x172)[0x55746c59bbdd]
postgres: standby_1: startup recovering 00000001000000000000000C(+0x3c4235)[0x55746c5a1235]
postgres: standby_1: startup recovering 00000001000000000000000C(PostmasterMain+0x1401)[0x55746c5a5a10]
postgres: standby_1: startup recovering 00000001000000000000000C(main+0x835)[0x55746c4e90ce]
/lib/x86_64-linux-gnu/libc.so.6(+0x276ca)[0x7f67bbb846ca]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x85)[0x7f67bbb84785]
postgres: standby_1: startup recovering 00000001000000000000000C(_start+0x21)[0x55746c2b61d1]

This refers to the following in twophase.c with
AdjustToFullTransactionId():
    nextXid = XidFromFullTransactionId(nextFullXid);
    epoch = EpochFromFullTransactionId(nextFullXid);

    if (unlikely(xid > nextXid))
    {
        /* Wraparound occurred, must be from a prev epoch. */
        Assert(epoch > 0);
        epoch--;
    }

This would mean that we've found a way to get a negative epoch, which
should not be possible.

Alexander, you have added this code in 5a1dfde8334b when switching the
2PC file names to use FullTransactionIds.  Could you check please?
--
Michael