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Re: BUG #19508: pg_buffercache_pages() crashes the backend with an incompatible caller-supplied record definition - Mailing list pgsql-bugs

From Ayush Tiwari
Subject Re: BUG #19508: pg_buffercache_pages() crashes the backend with an incompatible caller-supplied record definition
Date
Msg-id CAJTYsWX6b0UxeZ9HGGnju-XpWRmLr_y8AVeyWqd3gL+a0NkGtw@mail.gmail.com
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In response to Re: BUG #19508: pg_buffercache_pages() crashes the backend with an incompatible caller-supplied record definition  (Fujii Masao <masao.fujii@gmail.com>)
Responses Re: BUG #19508: pg_buffercache_pages() crashes the backend with an incompatible caller-supplied record definition
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Hi,

On Fri, 5 Jun 2026 at 08:49, Fujii Masao <masao.fujii@gmail.com> wrote:

Commit 257c8231bf9 changed pg_buffercache_pages() to materialize rows directly
into a tuplestore. As a result, the function started using the caller-supplied
RECORD descriptor as rsinfo->setDesc, so a mismatched column definition list
could cause tuplestore_putvalues() to interpret returned Datums with incorrect
types.

Before that change, pg_buffercache_pages() exposed its actual tuple descriptor
to the executor, allowing the executor's existing rowtype checks to reject
incompatible definitions with a normal error.

The attached patch restores that behavior while keeping the materialized-SRF
implementation. Thoughts?

Thanks for the patch, Fujii-san!

I was looking into the bug last night, and the approach looks right to me.

This still means InitMaterializedSRF() briefly creates the caller-derived
descriptor before rsinfo->setDesc is replaced. That seems acceptable here:
the descriptor lives only in the per-query context, and avoiding a local
copy of InitMaterializedSRF() keeps the fix much smaller and less fragile.

One small nit: build_buffercache_pages_tupledesc() names attribute 8
"usage_count", while the existing pg_buffercache view and the test use
"usagecount". This probably does not affect the tupledesc_match() check,
but I think it would be better to keep the existing spelling for
consistency.

Regards,
Ayush

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