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RE: WIP: WAL prefetch (another approach)

Shinoda, Noriyoshi <noriyoshi.shinoda@hpe.com>

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From: "Shinoda, Noriyoshi (PN Japan FSIP)" <noriyoshi.shinoda@hpe.com>
To: Thomas Munro <thomas.munro@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>, Stephen Frost <sfrost@snowman.net>, Andres Freund <andres@anarazel.de>, Jakub Wartak <Jakub.Wartak@tomtom.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, "Tomas Vondra" <tomas.vondra@2ndquadrant.com>, Dmitry Dolgov <9erthalion6@gmail.com>, David Steele <david@pgmasters.net>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-04-12T09:01:51Z
Lists: pgsql-hackers

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Hi, 
Thank you for developing the great feature. I tested this feature and checked the documentation. Currently, the documentation for the pg_stat_prefetch_recovery view is included in the description for the pg_stat_subscription view.

https://www.postgresql.org/docs/devel/monitoring-stats.html#MONITORING-PG-STAT-SUBSCRIPTION

It is also not displayed in the list of "28.2. The Statistics Collector".
https://www.postgresql.org/docs/devel/monitoring.html

The attached patch modifies the pg_stat_prefetch_recovery view to appear as a separate view.

Regards,
Noriyoshi Shinoda
-----Original Message-----
From: Thomas Munro <thomas.munro@gmail.com> 
Sent: Friday, April 8, 2022 10:47 AM
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>; Stephen Frost <sfrost@snowman.net>; Andres Freund <andres@anarazel.de>; Jakub Wartak <Jakub.Wartak@tomtom.com>; Alvaro Herrera <alvherre@2ndquadrant.com>; Tomas Vondra <tomas.vondra@2ndquadrant.com>; Dmitry Dolgov <9erthalion6@gmail.com>; David Steele <david@pgmasters.net>; pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: WIP: WAL prefetch (another approach)

On Fri, Apr 8, 2022 at 12:55 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
> The docs seem to be wrong about the default.
>
> +        are not yet in the buffer pool, during recovery.  Valid values are
> +        <literal>off</literal> (the default), <literal>on</literal> and
> +        <literal>try</literal>.  The setting <literal>try</literal> 
> + enables

Fixed.

> +   concurrency and distance, respectively.  By default, it is set to
> +   <literal>try</literal>, which enabled the feature on systems where
> +   <function>posix_fadvise</function> is available.
>
> Should say "which enables".

Fixed.

> Curiously, I reported a similar issue last year.

Sorry.  I guess both times we only agreed on what the default should be in the final review round before commit, and I let the docs get out of sync (well, the default is mentioned in two places and I apparently ended my search too soon, changing only one).  I also found another recently obsoleted sentence: the one about showing nulls sometimes was no longer true.  Removed.

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