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Re: WIP: WAL prefetch (another approach)

Julien Rouhaud <rjuju123@gmail.com>

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From: Julien Rouhaud <rjuju123@gmail.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: 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: 2022-03-14T07:17:13Z
Lists: pgsql-hackers 
On Mon, Mar 14, 2022 at 06:15:59PM +1300, Thomas Munro wrote:
> On Fri, Mar 11, 2022 at 9:27 PM Julien Rouhaud <rjuju123@gmail.com> wrote:
> > > > Also, is it worth an assert (likely at the top of the function) for that?
> > >
> > > How could I assert that EndRecPtr has the right value?
> >
> > Sorry, I meant to assert that some value was assigned (!XLogRecPtrIsInvalid).
> > It can only make sure that the first call is done after XLogBeginRead /
> > XLogFindNextRecord, but that's better than nothing and consistent with the top
> > comment.
>
> Done.

Just a small detail: I would move that assert at the top of the function as it
should always be valid.
>
> I also fixed the compile failure with -DWAL_DEBUG, and checked that
> output looks sane with wal_debug=on.

Great!  I'm happy with 0001 and I think it's good to go!
>
> > > The other thing I need to change is that I should turn on
> > > recovery_prefetch for platforms that support it (ie Linux and maybe
> > > NetBSD only for now), in the tests.  Right now you need to put
> > > recovery_prefetch=on in a file and then run the tests with
> > > "TEMP_CONFIG=path_to_that make -C src/test/recovery check" to
> > > excercise much of 0002.
> >
> > +1 with Andres' idea to have a "try" setting.
>
> Done.  The default is still "off" for now, but in
> 027_stream_regress.pl I set it to "try".

Great too!  Unless you want to commit both patches right now I'd like to review
0002 too (this week), as I barely look into it for now.

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