Horton

Re: Streaming read-ready sequential scan code

Alexander Law <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Andres Freund <andres@anarazel.de>, Thomas Munro <thomas.munro@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>
Cc: David Rowley <dgrowleyml@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2024-05-17T13:00:00Z
Lists: pgsql-hackers

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Hello,

I decided to compare v17 vs v16 performance (as I did the last year [1])
and discovered that v17 loses to v16 in the pg_tpcds (s64da_tpcds)
benchmark, query15 (and several others, but I focused on this one):
Best pg-src-master--.* worse than pg-src-16--.* by 52.2 percents (229.84 > 151.03): pg_tpcds.query15
Average pg-src-master--.* worse than pg-src-16--.* by 53.4 percents (234.20 > 152.64): pg_tpcds.query15
Please look at the full html report attached in case you're interested.

(I used my pg-mark tool to measure/analyze performance, but I believe the
same results can be seen without it.)

`git bisect` for this performance degradation pointed at b7b0f3f27...

[1] https://www.postgresql.org/message-id/b32bed1b-0746-9b20-1472-4bdc9ca66d52%40gmail.com

Best regards,
Alexander

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