Horton

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

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Kartyshov Ivan <i.kartyshov@postgrespro.ru>, dilipbalaut@gmail.com, smithpb2250@gmail.com, pgsql-hackers@lists.postgresql.org
Date: 2024-03-16T10:56:22Z
Lists: pgsql-hackers 
On Fri, Mar 15, 2024 at 7:50 PM Alexander Korotkov <aekorotkov@gmail.com> wrote:
>
> I went through this patch another time, and made some minor
> adjustments.  Now it looks good, I'm going to push it if no
> objections.
>

I have a question related to usability, if the regular reads (say a
Select statement or reads via function/procedure) need a similar
guarantee to see the changes on standby then do they also always need
to first do something like "BEGIN AFTER '0/3F0FF791' WITHIN 1000;"? Or
in other words, shouldn't we think of something for implicit
transactions?

In general, it seems this patch has been stuck for a long time on the
decision to choose an appropriate UI (syntax), and we thought of
moving it further so that the other parts of the patch can be
reviewed/discussed. So, I feel before pushing this we should see
comments from a few (at least two) other senior members who earlier
shared their opinion on the syntax. I know we don't have much time
left but OTOH pushing such a change (where we didn't have a consensus
on syntax) without much discussion at this point of time could lead to
discussions after commit.

-- 
With Regards,
Amit Kapila.

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