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Re: Parallel Bitmap Heap Scan reports per-worker stats in EXPLAIN ANALYZE

Tomas Vondra <tomas@vondra.me>

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From: Tomas Vondra <tomas@vondra.me>
To: David Rowley <dgrowleyml@gmail.com>, Masahiro.Ikeda@nttdata.com
Cc: lena.ribackina@yandex.ru, donghanglin@gmail.com, geidav.pg@gmail.com, melanieplageman@gmail.com, tomas.vondra@enterprisedb.com, dilipbalaut@gmail.com, pgsql-hackers@lists.postgresql.org, hlinnaka@iki.fi
Date: 2026-04-03T19:20:16Z
Lists: pgsql-hackers 
Hi,

I'm working on adding information about prefetching for scans [1], which
includes BitmapHeapScan. I realized the instrumentation added by this
thread may not be quite right, resulting in missing instrumentation for
non-parallel-aware scans in a parallel query.

A better description / explanation of the issue is posted here [2]. I've
posted a proposed fix in the following message [3], in a patch:

  v8-0002-Show-Bitmap-Heap-Scan-stats-for-non-parallel-awar.patch

I wonder if someone from this thread could review my analysis, and
confirm this is not intentional. I don't see it discussed in the thread,
so I assume no one noticed this behavior. I'd also appreciate a review
of the proposed fix, or suggestions for alternative fixes.

regards


[1]
https://www.postgresql.org/message-id/a177a6dd-240b-455a-8f25-aca0b1c08c6e%40vondra.me

[2]
https://www.postgresql.org/message-id/3bdbc70d-ad44-494a-8aab-868b5066fe8b%40vondra.me

[3]
https://www.postgresql.org/message-id/fce326bb-1210-4d48-8c97-bb3bca396eba%40vondra.me

-- 
Tomas Vondra

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Show Parallel Bitmap Heap Scan worker stats in EXPLAIN ANALYZE

  2. Widen lossy and exact page counters for Bitmap Heap Scan

  3. Remove redundant snapshot copying from parallel leader to workers