Horton

Re: Streaming read-ready sequential scan code

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Melanie Plageman <melanieplageman@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Pg Hackers <pgsql-hackers@postgresql.org>, David Rowley <dgrowleyml@gmail.com>
Date: 2024-04-04T09:31:57Z
Lists: pgsql-hackers

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On Thu, Apr 4, 2024 at 11:13 AM Andres Freund <andres@anarazel.de> wrote:
> The / 2 is to avoid causing unnecessarily frequent WAL flushes, right? If so,
> should we apply that only if the ring the strategy doesn't use the
> StrategyRejectBuffer() logic?

Hmm, I don't really know, but that sounds plausible.  What do you
think about the attached?

> I think for VACUUM we should probably go a bit further. There's no comparable
> L1/L2 issue, because the per-buffer processing + WAL insertion is a lot more
> expensive, compared to a seqscan. I'd go or at lest 4x-8x.

Alright what about this?

Commits

  1. Fix unfairness in all-cached parallel seq scan.

  2. Fix if/while thinko in read_stream.c edge case.

  3. Increase default vacuum_buffer_usage_limit to 2MB.

  4. Allow BufferAccessStrategy to limit pin count.

  5. Improve read_stream.c's fast path.

  6. Secondary refactor of heap scanning functions

  7. Preliminary refactor of heap scanning functions

  8. Add VACUUM/ANALYZE BUFFER_USAGE_LIMIT option