Horton
Menu

Re: WIP: WAL prefetch (another approach)

Thomas Munro <thomas.munro@gmail.com>

View thread
From: Thomas Munro <thomas.munro@gmail.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: 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: 2021-04-07T11:24:25Z
Lists: pgsql-hackers

Attachments

Here's rebase, on top of Horiguchi-san's v19 patch set.  My patches
start at 0007.  Previously, there was a "nowait" flag that was passed
into all the callbacks so that XLogReader could wait for new WAL in
some cases but not others.  This new version uses the proposed
XLREAD_NEED_DATA protocol, and the caller deals with waiting for data
to arrive when appropriate.  This seems tidier to me.

I made one other simplifying change: previously, the prefetch module
would read the WAL up to the "written" LSN (so, allowing itself to
read data that had been written but not yet flushed to disk by the
walreceiver), though it still waited until a record's LSN was
"flushed" before replaying.  That allowed prefetching to happen
concurrently with the WAL flush, which was nice, but it felt a little
too "special".  I decided to remove that part for now, and I plan to
look into making standbys work more like primary servers, using WAL
buffers, the WAL writer and optionally the standard log-before-data
rule.

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