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: Kartyshov Ivan <i.kartyshov@postgrespro.ru>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2023-12-08T10:27:16Z
Lists: pgsql-hackers 
On Fri, Dec 8, 2023 at 11:20 AM Kartyshov Ivan
<i.kartyshov@postgrespro.ru> wrote:
>
> On 2023-11-27 03:08, Alexander Korotkov wrote:
> > I've retried my case with v6 and it doesn't fail anymore.  But I
> > wonder how safe it is to reset xmin within the user-visible function?
> > We have no guarantee that the function is not called inside the
> > complex query.  Then how will the rest of the query work with xmin
> > reset?  Separate utility statement still looks like more safe option
> > for me.
>
> As you mentioned, we can`t guarantee that the function is not called
> inside the complex query, but we can return the xmin after waiting.

Returning xmin back isn't safe.  Especially after potentially long
waiting.  The snapshot could be no longer valid, because the
corresponding tuples could be VACUUM'ed.

------
Regards,
Alexander Korotkov

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