Horton

Re: Postgres 11 release notes

David Rowley <david.rowley@2ndquadrant.com>

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From: David Rowley <david.rowley@2ndquadrant.com>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>, Bruce Momjian <bruce@momjian.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-05-21T07:34:18Z
Lists: pgsql-hackers 
On 19 May 2018 at 03:58, Amit Langote <amitlangote09@gmail.com> wrote:
> I wonder what you think about including this little performance item:
>
> https://www.postgresql.org/message-id/E1eotSQ-0005V0-LV@gemulon.postgresql.org
>
> especially considering the part of the commit message which states
>
> ...Still, testing shows
> that this makes single-row inserts significantly faster on a table
> with many partitions without harming the bulk-insert case.
>
> I recall seeing those inserts being as much as 2x faster as partition
> count grows beyond hundreds.  One might argue that we should think
> about publicizing this only after we've dealt with the
> lock-all-partitions issue that's also mentioned in the commit message
> which is still a significant portion of the time spent and I'm totally
> fine with that.

While I do think that was a good change, I do think there's much still
left to do to speed up usage of partitioned tables with many
partitions.

I've been working a bit in this area over the past few weeks and with
PG11 I measured a single INSERT into a 10k RANGE partitioned table at
just 84 tps (!), while inserting the same row into a non-partitioned
table was about 11.1k tps. I have patches locally that take this up to
~9.8k tps, which I'll submit for PG12. I'm unsure if we should be
shouting anything from the rooftops about the work done in this area
for PG11, since it's still got a long way to go still before the
feature is usable with higher numbers of partitions. I do think your
change was a good one to make, but I just don't want users to think
that we're done here when we all know that much work remains.

If we're going to add an item in the release notes about this then I
wouldn't object, providing it could be done in a way that indicates
we've not finished here yet, but if that's the case then maybe it's
better to say nothing at all.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Commits

  1. doc: update PG 11 release notes

  2. Fix misspelled pg_trgm contrib name in PostgreSQL 11 release notes

  3. Doc: clarify release note text about v11's new window function features.

  4. Improve wording of release notes item

  5. Fix typos in release notes

  6. Doc: preliminary list of PG11 major features.

  7. Make numeric power() handle NaNs according to the modern POSIX spec.

  8. Various improvements of skipping index scan during vacuum technics

  9. Revert back-branch changes in power()'s behavior for NaN inputs.

  10. Avoid wrong results for power() with NaN input on more platforms.

  11. Avoid wrong results for power() with NaN input on some platforms.

  12. Skip full index scan during cleanup of B-tree indexes when possible

  13. Rewrite the code that applies scan/join targets to paths.

  14. Postpone generate_gather_paths for topmost scan/join rel.

  15. Add casts from jsonb

  16. Make plpgsql use its DTYPE_REC code paths for composite-type variables.

  17. Don't allow VACUUM VERBOSE ANALYZE VERBOSE.

  18. Pass InitPlan values to workers via Gather (Merge).

  19. Account for the effect of lossy pages when costing bitmap scans.

  20. Allow no-op GiST support functions to be omitted.

  21. Rearm statement_timeout after each executed query.

  22. Push limit through subqueries to underlying sort, where possible.