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Re: WIP: WAL prefetch (another approach)

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Thomas Munro <thomas.munro@gmail.com>, Ashutosh Sharma <ashu.coek88@gmail.com>
Cc: 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>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-03-08T13:48:54Z
Lists: pgsql-hackers 

On 3/8/22 06:15, Thomas Munro wrote:
> On Wed, Dec 29, 2021 at 5:29 PM Thomas Munro <thomas.munro@gmail.com> wrote:
>> https://github.com/macdice/postgres/tree/recovery-prefetch-ii
> 
> Here's a rebase.  This mostly involved moving hunks over to the new
> xlogrecovery.c file.  One thing that seemed a little strange to me
> with the new layout is that xlogreader is now a global variable.  I
> followed that pattern and made xlogprefetcher a global variable too,
> for now.
> 
> There is one functional change: now I block readahead at records that
> might change the timeline ID.  This removes the need to think about
> scenarios where "replay TLI" and "read TLI" might differ.  I don't
> know of a concrete problem in that area with the previous version, but
> the recent introduction of the variable(s) "replayTLI" and associated
> comments in master made me realise I hadn't analysed the hazards here
> enough.  Since timelines are tricky things and timeline changes are
> extremely infrequent, it seemed better to simplify matters by putting
> up a big road block there.
> 
> I'm now starting to think about committing this soon.

+1. I don't have the capacity/hardware to do more testing at the moment,
but all of this looks reasonable.


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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