Horton

Re: [HACKERS] make async slave to wait for lsn to be replayed

Alexander Korotkov <aekorotkov@gmail.com>

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From: Alexander Korotkov <aekorotkov@gmail.com>
To: Kevin Hale Boyes <kcboyes@gmail.com>
Cc: Kartyshov Ivan <i.kartyshov@postgrespro.ru>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, hlinnaka@iki.fi, alvherre@alvh.no-ip.org, pashkin.elfe@gmail.com, bharath.rupireddyforpostgres@gmail.com, euler@eulerto.com, thomas.munro@gmail.com, peter@eisentraut.org, amit.kapila16@gmail.com, dilipbalaut@gmail.com, smithpb2250@gmail.com, pgsql-hackers@lists.postgresql.org
Date: 2024-08-06T02:17:10Z
Lists: pgsql-hackers

Attachments

On Sat, Aug 3, 2024 at 6:07 AM Alexander Korotkov <aekorotkov@gmail.com> wrote:
> On Sat, Aug 3, 2024 at 3:45 AM Kevin Hale Boyes <kcboyes@gmail.com> wrote:
> > In the for loop in WaitForLSNReplay, shouldn't the check for in-recovery be moved up above the call to GetXLogReplayRecPtr?
> > If we get promoted while waiting for the timeout we could call GetXLogReplayRecPtr while not in recovery.
>
> This is intentional.  After standby gets promoted,
> GetXLogReplayRecPtr() returns the last WAL position being replayed
> while being standby.  So, if standby reached target lsn before being
> promoted, we don't have to throw an error.
>
> But this gave me an idea that before the loop we probably need to put
> RecoveryInProgress() check after GetXLogReplayRecPtr() too.  I'll
> recheck that.

The attached patchset comprises assorted improvements for pg_wal_replay_wait().

The 0001 patch is intended to improve this situation.  Actually, it's
not right to just put RecoveryInProgress() after
GetXLogReplayRecPtr(), because more wal could be replayed between
these calls.  Instead we need to recheck GetXLogReplayRecPtr() after
getting negative result of RecoveryInProgress() because WAL replay
position couldn't get updated after.
0002 patch comprises fix for the header comment of WaitLSNSetLatches() function
0003 patch comprises tests for pg_wal_replay_wait() errors.

------
Regards,
Alexander Korotkov
Supabase

Commits

  1. Ensure standby promotion point in 043_wal_replay_wait.pl

  2. Minor cleanup related to pg_wal_replay_wait() procedure

  3. Adjust pg_wal_replay_wait() procedure behavior on promoted standby

  4. pg_wal_replay_wait(): Fix typo in the doc

  5. Implement pg_wal_replay_wait() stored procedure

  6. Revert: Implement pg_wal_replay_wait() stored procedure

  7. Call WaitLSNCleanup() in AbortTransaction()

  8. Clarify what is protected by WaitLSNLock

  9. Use an LWLock instead of a spinlock in waitlsn.c

  10. Use the pairing heap instead of a flat array for LSN replay waiters

  11. Minor improvements for waitlsn.c

  12. Make the order of the header file includes consistent