| From: | Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com> |
|---|---|
| To: | shihao zhong <zhong950419(at)gmail(dot)com> |
| Cc: | Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Melanie Plageman <melanieplageman(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
| Subject: | Re: Fix ReadStream handling when heap rescan strategy changes |
| Date: | 2026-11-04 08:37:48 |
| Message-ID: | auru3LY+yQtf6QIk@bdtpg |
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| Thread: | |
| Lists: | pgsql-hackers |
Hi Shihao,
On Tue, Nov 03, 2026 at 10:32:25PM -0500, shihao zhong wrote:
> Hi Bertrand,
>
> I am not sure the dangling pointer case can happen on master today.
>
> initscan() only frees the strategy if SO_ALLOW_STRAT gets cleared or
> the table drops below NBuffers / 4. The only caller of
> table_rescan_set_params() is SampleScan, and a sample scan has no read
> stream on master.
>
> I don't think the table can shrink either, because truncation takes an AE
> today.
Thanks for looking at it!
I think that an extension can trigger it without shrinking the relation: start
a large sequential scan with allow_strat = true, then call table_rescan_set_params()
with allow_strat = false.
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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