Horton

Re: Postgres 11 release notes

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Bruce Momjian <bruce@momjian.us>
Cc: Teodor Sigaev <teodor@sigaev.ru>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-05-11T19:04:10Z
Lists: pgsql-hackers 
On 2018-05-11 14:59:04 -0400, Bruce Momjian wrote:
> On Fri, May 11, 2018 at 11:50:51AM -0700, Andres Freund wrote:
> > On 2018-05-11 14:44:06 -0400, Bruce Momjian wrote:
> > > On Fri, May 11, 2018 at 07:49:50PM +0300, Teodor Sigaev wrote:
> > > > 
> > > > 
> > > > Bruce Momjian wrote:
> > > > >I have committed the first draft of the Postgres 11 release notes.  I
> > > > >will add more markup soon.  You can view the most current version here:
> > > > >
> > > > >	http://momjian.us/pgsql_docs/release-11.html
> > > > >
> > > > >I expect a torrent of feedback.  ;-)
> > > > Hi!
> > > > 
> > > > Seems, you miss:
> > > > 857f9c36cda520030381bd8c2af20adf0ce0e1d4 Skip full index scan during cleanup
> > > > of B-tree indexes when possible
> > > 
> > > I read that and thought it was too details to be in the release notes. 
> > > It is not that it is unimportant, but it is hard to see how people would
> > > notice the difference or change their behavior based on this change.
> > 
> > It's a *huge* performance problem in larger installations
> > currently. When you have a multi-TB relation and correspondingly large
> > relation, the VM allows to make the heap cleanups cheap, but then the
> > index scan takes just about forever.  I know at least one large PG user
> > that moved off postgres because of it.  This won't solve all of those
> > concerns, but it definitely is crucial to know for such users.
> > 
> > People would notice by vacuums of large relations not taking forever
> > anymore. And the behaviour change would be to a) upgrade b) tune the
> > associated reloption/GUC.
> 
> OK, so what is the text that people will understand?  This?
> 
> 	Prevent manual VACUUMs on append-only tables from performing
> 	needless index scans

I don't think the table being 'append-only' is necessary?  Nor does it
have to be a manual vacuum. And 'needless index scan' sounds less than
it is/was, namely a full scan of the index. Perhaps something like:

  Allow vacuum to skip doing a full scan of btree indexes after VACUUM,
  if not necessary.

or something like that?


> You can see why I was hesitant to include it, based on this text, but I
> am happy to add it.

I can't. Even if the above were accurate it'd be relevant information.

Greetings,

Andres Freund

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.