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: 2024-08-03T03:07:32Z
Lists: pgsql-hackers 
On Sat, Aug 3, 2024 at 3:45 AM Kevin Hale Boyes <kcboyes@gmail.com> wrote:
> I noticed the commit and had a question and a comment.
> There is a small problem in func.sgml in the sentence "After that the changes made of primary".  Should be "on primary".

Thank you for spotting this. Will fix.

> 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.

------
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