Message-ID: <326831c0-df02-435a-8c2c-428d59222a91@gmail.com>
Date: Thu, 16 Apr 2026 08:49:58 +0200
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Subject: Re: Parallel Bitmap Heap Scan reports per-worker stats in EXPLAIN
 ANALYZE
To: Melanie Plageman <melanieplageman@gmail.com>,
 Tomas Vondra <tomas@vondra.me>
Cc: David Rowley <dgrowleyml@gmail.com>, Masahiro.Ikeda@nttdata.com,
 lena.ribackina@yandex.ru, donghanglin@gmail.com,
 tomas.vondra@enterprisedb.com, dilipbalaut@gmail.com,
 pgsql-hackers@lists.postgresql.org, hlinnaka@iki.fi
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From: David Geier <geidav.pg@gmail.com>
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Hi Tomas!

On 05.04.2026 20:27, Melanie Plageman wrote:
> On Fri, Apr 3, 2026 at 3:20 PM Tomas Vondra <tomas@vondra.me> wrote:
>>
>> 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 haven't spent a lot of time looking through the code and your patch
but I'm wondering why we're not rather missing a
ExecBitmapIndexScanInstrumentEstimate(), rather than calling
ExecBitmapIndexScanEstimate() also in the !parallel_aware case. All
other scans do it this way, so why do it differently for Bitmap Index Scan?

>> 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.
> 
> I can't imagine this was intentional.

Agreed.

--
David Geier