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Re: WIP: WAL prefetch (another approach)

Stephen Frost <sfrost@snowman.net>

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From: Stephen Frost <sfrost@snowman.net>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, David Steele <david@pgmasters.net>, Dmitry Dolgov <9erthalion6@gmail.com>, Jakub Wartak <Jakub.Wartak@tomtom.com>, Tom Lane <tgl@sss.pgh.pa.us>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-04-21T23:22:33Z
Lists: pgsql-hackers 
Greetings,

On Wed, Apr 21, 2021 at 19:17 Thomas Munro <thomas.munro@gmail.com> wrote:

> On Thu, Apr 22, 2021 at 8:16 AM Thomas Munro <thomas.munro@gmail.com>
> wrote:
> > That wasn't my plan, but I admit that the timing was non-ideal.  In
> > any case, I'll dig into these failures and then consider options.
> > More soon.
>
> Yeah, this clearly needs more work.  xlogreader.c is difficult to work
> with and I think we need to keep trying to improve it, but I made a
> bad call here trying to combine this with other refactoring work up
> against a deadline and I made some dumb mistakes.  I could of course
> debug it in-tree, and I know that this has been an anticipated
> feature.  Personally I think the right thing to do now is to revert it
> and re-propose for 15 early in the cycle, supported with some better
> testing infrastructure.


I tend to agree with the idea to revert it, perhaps a +0 on that, but if
others argue it should be fixed in-place, I wouldn’t complain about it.

I very much encourage the idea of improving testing in this area and would
be happy to try and help do so in the 15 cycle.

Thanks,

Stephen

>

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix recovery_prefetch docs.

  2. Prefetch data referenced by the WAL, take II.

  3. Add circular WAL decoding buffer, take II.

  4. Fix generation of ./INSTALL for the distribution tarball

  5. Revert recovery prefetching feature.

  6. Sync guc.c and postgresql.conf.sample with the SGML docs.

  7. Add information of total data processed to replication slot stats.

  8. Doc: Review for "Optionally prefetch referenced data in recovery."

  9. Add circular WAL decoding buffer.

  10. Optionally prefetch referenced data in recovery.

  11. Remove read_page callback from XLogReader.

  12. Provide ReadRecentBuffer() to re-pin buffers by ID.

  13. Provide recovery_init_sync_method=syncfs.

  14. Mark factorial operator, and postfix operators in general, as deprecated.

  15. Rationalize GetWalRcv{Write,Flush}RecPtr().

  16. Support PrefetchBuffer() in recovery.

  17. Prevent hard failures of standbys caused by recycled WAL segments