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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: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Cc: Simon Riggs <simon.riggs@enterprisedb.com>, Julien Rouhaud <rjuju123@gmail.com>, Ashutosh Sharma <ashu.coek88@gmail.com>, Daniel Gustafsson <daniel@yesql.se>, Stephen Frost <sfrost@snowman.net>, 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: 2022-09-25T02:31:37Z
Lists: pgsql-hackers 
On Wed, Apr 13, 2022 at 8:05 AM Thomas Munro <thomas.munro@gmail.com> wrote:
> On Wed, Apr 13, 2022 at 3:57 AM Dagfinn Ilmari Mannsåker
> <ilmari@ilmari.org> wrote:
> > Simon Riggs <simon.riggs@enterprisedb.com> writes:
> > > This is a nice feature if it is safe to turn off full_page_writes.

> > > When is it safe to do that? On which platform?
> > >
> > > I am not aware of any released software that allows full_page_writes
> > > to be safely disabled. Perhaps something has been released recently
> > > that allows this? I think we have substantial documentation about
> > > safety of other settings, so we should carefully document things here
> > > also.
> >
> > Our WAL reliability docs claim that ZFS is safe against torn pages:
> >
> > https://www.postgresql.org/docs/current/wal-reliability.html:
> >
> >     If you have file-system software that prevents partial page writes
> >     (e.g., ZFS), you can turn off this page imaging by turning off the
> >     full_page_writes parameter.
>
> Unfortunately, posix_fadvise(WILLNEED) doesn't do anything on ZFS
> right now :-(.

Update: OpenZFS now has this working in its master branch (Linux only
for now), so fingers crossed for the next release.

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