Horton

Re: First draft of the PG 15 release notes

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Euler Taveira <euler@eulerto.com>
Cc: Bruce Momjian <bruce@momjian.us>, Ajin Cherian <itsajin@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-05-13T02:54:53Z
Lists: pgsql-hackers 
On Fri, May 13, 2022 at 6:02 AM Euler Taveira <euler@eulerto.com> wrote:
>
> On Thu, May 12, 2022, at 11:22 AM, Bruce Momjian wrote:
>
> On Thu, May 12, 2022 at 11:12:54AM -0300, Euler Taveira wrote:
> OB> On Thu, May 12, 2022, at 11:03 AM, Bruce Momjian wrote:
> >
> >     I looked at that but thought that everyone would already assume we
> >     skipped replication of empty transactions, and I didn't see much impact
> >     for the user, so I didn't include it.
> >
> > It certainly has an impact on heavy workloads that replicate tables with few
> > modifications. It receives a high traffic of 'begin' and 'commit' messages that
> > the previous Postgres versions have to handle (discard). I would classify it as
> > a performance improvement for logical replication. Don't have a strong opinion
> > if it should be mentioned or not.
>
> Oh, so your point is that a transaction that only has SELECT would
> previously send an empty transaction?  I thought this was only for apps
> that create literal empty transactions, which seem rare.
>
> No. It should be a write transaction. If you have a replication setup that
> publish only table foo (that isn't modified often) and most of your
> workload does not contain table foo, Postgres sends 'begin' and 'commit'
> messages to subscriber even if there is no change to replicate.
>

It reduces network traffic and improves performance by 3-14% on simple
tests [1] like the one shown by Euler. I see a value in adding this as
for the workloads where it hits, it seems more than 99% of network
traffic [2] is due to these empty messages.

[1] - https://www.postgresql.org/message-id/OSZPR01MB63105A71CFAA46F5BD7C9D7CFD1E9%40OSZPR01MB6310.jpnprd01.prod.outlook.com
[2] - https://www.postgresql.org/message-id/CAMkU=1yohp9-dv48FLoSPrMqYEyyS5ZWkaZGD41RJr10xiNo_Q@mail.gmail.com

-- 
With Regards,
Amit Kapila.

Commits

  1. Doc: last minute adjustment to the release notes

  2. Doc: more tweaking of v15 release notes.

  3. Doc: further adjust notes about pg_upgrade_output.d.

  4. Doc: add list of major features to the v15 release notes.

  5. relnotes: update item about public schema permission change

  6. relnotes: update ordered partition scan item

  7. relnotes: add Heikki to UTF8 item

  8. relnotes: improve UTF8 text item in relation to ASCII

  9. relnotes: add null logical replication item

  10. relnotes: adjust several logical replication items and FK text

  11. relnotes: mention non-exclusive backup mode was deprecated

  12. relnotes: add author to in-memory sorts item

  13. relnotes: update for non-exclusive backup mode removal

  14. relnote: improve sorting entries

  15. relnotes: adjustments from Álvaro Herrera

  16. relnotes: update foreign key partition and add sort items

  17. relnotes: more adjustments

  18. relnotes: logical replication permissions checked by subscrib.

  19. relnotes: adjustments

  20. relnotes: remove sequence replication and update 'postgres -C'

  21. relnote: extensive updates

  22. relnotes: "training" -> "trailing"

  23. Standardize references to Zstandard as <productname>

  24. pgstat: Update docs to match the shared memory stats reality.

  25. Raise a WARNING for missing publications.

  26. Skip empty transactions for logical replication.

  27. Optionally disable subscriptions on error.

  28. Allow root-owned SSL private keys in libpq, not only the backend.

  29. Use COPY FREEZE in pgbench for faster benchmark table population.