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Re: WIP: WAL prefetch (another approach)

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Jakub Wartak <Jakub.Wartak@tomtom.com>, Stephen Frost <sfrost@snowman.net>, Alvaro Herrera <alvherre@2ndquadrant.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Dmitry Dolgov <9erthalion6@gmail.com>, David Steele <david@pgmasters.net>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2020-12-30T03:57:36Z
Lists: pgsql-hackers 
Hi,

On 2020-12-24 16:06:38 +1300, Thomas Munro wrote:
> From 85187ee6a1dd4c68ba70cfbce002a8fa66c99925 Mon Sep 17 00:00:00 2001
> From: Thomas Munro <thomas.munro@gmail.com>
> Date: Sat, 28 Mar 2020 11:42:59 +1300
> Subject: [PATCH v15 1/6] Add pg_atomic_unlocked_add_fetch_XXX().
> 
> Add a variant of pg_atomic_add_fetch_XXX with no barrier semantics, for
> cases where you only want to avoid the possibility that a concurrent
> pg_atomic_read_XXX() sees a torn/partial value.  On modern
> architectures, this is simply value++, but there is a fallback to
> spinlock emulation.

Wouldn't it be sufficient to implement this as one function implemented as
    pg_atomic_write_u32(val, pg_atomic_read_u32(val) + 1)
then we'd not need any ifdefs?



> + * pg_atomic_unlocked_add_fetch_u32 - atomically add to variable

It's really not adding "atomically"...


> + * Like pg_atomic_unlocked_write_u32, guarantees only that partial values
> + * cannot be observed.

Maybe add a note saying that that in particularly means that
modifications could be lost when used concurrently?


Greetings,

Andres Freund

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