Message-ID: <7b8ba18a-548c-4a2f-962c-e50a3f902607@vondra.me>
Date: Sun, 5 Apr 2026 21:40:48 +0200
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Subject: Re: Parallel Bitmap Heap Scan reports per-worker stats in EXPLAIN
 ANALYZE
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: David Rowley <dgrowleyml@gmail.com>, Masahiro.Ikeda@nttdata.com,
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From: Tomas Vondra <tomas@vondra.me>
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On 4/5/26 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 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.
> 

Indeed.

> I reviewed your approach and suggest we aim for even lower impact by
> always allocating the ParallelBitmapHeapState. That means the DSM
> layout won't differ such that pcxt->toc has to point to the
> instrumentation in the parallel-oblivious case and the pstate in the
> parallel-aware case. Attached is a patch that does this.
> 

I like this approach - it's much simpler / less invasive. It did not
occur to me to use the parallel_aware in BitmapTableScanSetup.


regards

-- 
Tomas Vondra