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: Andy Fan <zhihuifan1213@163.com>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Kartyshov Ivan <i.kartyshov@postgrespro.ru>, Euler Taveira <euler@eulerto.com>, Thomas Munro <thomas.munro@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, Amit Kapila <amit.kapila16@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Peter Smith <smithpb2250@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2024-04-02T12:31:40Z
Lists: pgsql-hackers 
On Tue, Apr 2, 2024 at 2:47 PM Andy Fan <zhihuifan1213@163.com> wrote:
> Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> writes:
>
> > On Tue, Apr 2, 2024 at 3:41 PM Kartyshov Ivan
> > <i.kartyshov@postgrespro.ru> wrote:
> >>
> >> 8 years, we tried to add this feature, and now we suggest the best way
> >> for this feature is to commit the minimal version first.
> >
> > Just curious, do you or anyone else have an immediate use for this
> > function? If yes, how are they achieving read-after-write-consistency
> > on streaming standbys in their application right now without a
> > function like this?
>
> The link [1] may be helpful and I think the reason there is reasonable
> to me.
>
> Actually we also disucss how to make sure the "read your writes
> consistency" internally, and the soluation here looks good to me.
>
> Glad to know that this patch will be committed very soon.
>
> [1]
> https://www.postgresql.org/message-id/CAPpHfdtuiL1x4APTs7u1fCmxkVp2-ZruXcdCfprDMdnOzvdC%2BA%40mail.gmail.com

Thank you for your feedback.

I also can confirm that a lot of users would be very happy to have
"read your writes consistency" and ready to do something to achieve
this at an application level.  However, they typically don't know what
exactly they need.

So, blogging about pg_wal_replay_wait() and spreading words about it
at conferences would be highly appreciated.

------
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