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Re: WIP: WAL prefetch (another approach)

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Michael Paquier <michael.paquier@gmail.com>, Stephen Frost <sfrost@snowman.net>, Alvaro Herrera <alvherre@2ndquadrant.com>, David Steele <david@pgmasters.net>, Dmitry Dolgov <9erthalion6@gmail.com>, Jakub Wartak <Jakub.Wartak@tomtom.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-04-29T04:27:36Z
Lists: pgsql-hackers 
On Thu, Apr 29, 2021 at 3:14 PM Andres Freund <andres@anarazel.de> wrote:
> To me it looks like a smaller version of the problem is present in < 14,
> albeit only when the page header is at a record boundary. In that case
> we don't validate the page header immediately, only once it's completely
> read. But we do believe the total size, and try to allocate
> that.
>
> There's a really crufty escape hatch (from 70b4f82a4b) to that:

Right, I made that problem worse, and that could probably be changed
to be no worse than 13 by reordering those operations.

PS Sorry for my intermittent/slow responses on this thread this week,
as I'm mostly away from the keyboard due to personal commitments.
I'll be back in the saddle next week to tidy this up, most likely by
reverting.  The main thought I've been having about this whole area is
that, aside from the lack of general testing of recovery, which we
should definitely address[1], what it really needs is a decent test
harness to drive it through all interesting scenarios and states at a
lower level, independently.

[1] https://www.postgresql.org/message-id/flat/CA%2BhUKGKpRWQ9SxdxxDmTBCJoR0YnFpMBe7kyzY8SUQk%2BHeskxg%40mail.gmail.com

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