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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: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@gmail.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Dmitry Dolgov <9erthalion6@gmail.com>, David Steele <david@pgmasters.net>, Alvaro Herrera <alvherre@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2020-12-04T19:01:45Z
Lists: pgsql-hackers 
Greetings,

* Andres Freund (andres@anarazel.de) wrote:
> On 2020-12-04 13:27:38 -0500, Stephen Frost wrote:
> > If I follow correctly, this patch will scan ahead in the WAL and let
> > the kernel know that certain blocks will be needed soon.  Ideally,
> > though I don't think it does yet, we'd only do that for blocks that
> > aren't already in shared buffers, and only for non-FPIs (even better if
> > we can skip past pages for which we already, recently, passed an FPI).
> 
> The patch uses PrefetchSharedBuffer(), which only initiates a prefetch
> if the page isn't already in s_b.

Great, glad that's already been addressed in this, that's certainly
good.  I think I knew that and forgot it while composing that response
over the past rather busy week. :)

> And once we have AIO, it can actually initiate IO into s_b at that
> point, rather than fetching it just into the kernel page cache.

Sure.

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