From: Michael Paquier <michael@paquier.xyz>
To: suyu.cmj <mengjuan.cmj@alibaba-inc.com>
Cc: pgsql-bugs <pgsql-bugs@lists.postgresql.org>
Subject: Re: Got FATAL in lock_twophase_recover() during recovery
Date: Wed, 12 Jul 2023 08:41:45 +0900
Message-ID: <ZK3oueit2kXFZujm@paquier.xyz> (raw)
In-Reply-To: <92895db6-5ae2-41f1-8038-302c31712691.mengjuan.cmj@alibaba-inc.com>
References: <92895db6-5ae2-41f1-8038-302c31712691.mengjuan.cmj@alibaba-inc.com>
On Tue, Jul 11, 2023 at 10:35:15AM +0800, suyu.cmj wrote:
> 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;
It looks like you have something here. I'll try to look at it. This
is a bug, so I have removed pgsql-hackers from the CC list keeping
only pgsql-bugs as cross-list posts are not encouraged.
--
Michael
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To: pgsql-bugs@postgresql.org
Cc: michael@paquier.xyz, mengjuan.cmj@alibaba-inc.com, pgsql-bugs@lists.postgresql.org
Subject: Re: Got FATAL in lock_twophase_recover() during recovery
In-Reply-To: <ZK3oueit2kXFZujm@paquier.xyz>
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