MIME-Version: 1.0
From: Siddharth Kothari <sidkot@google.com>
Date: Wed, 18 Feb 2026 15:09:15 +0530
Message-ID: <CAGCUe0Kp7kTUWFjHhiE-xjZ4=UDe2fUdDVajKcjV+BT+T5d21A@mail.gmail.com>
Subject: [PATCH] Add RetrieveInstrumentation hook for CustomScan providers
To: pgsql-hackers@lists.postgresql.org
Cc: Vaibhav Jain <jainva@google.com>, Madhukar <madhukarprasad@google.com>
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Dear PostgreSQL Hackers,

This email proposes a patch to enhance the CustomScan provider interface.
The patch file,
0001-Add-RetrieveInstrumentationCustomScan-hook-for-Custo.patch, is
attached.

*Problem:*

CustomScan providers currently lack a standard method to aggregate
instrumentation data from parallel workers back to the leader process
before the Dynamic Shared Memory (DSM) segment is unlinked. This makes it
difficult to gather comprehensive performance metrics from parallelized
custom scans.

*Solution:*

This patch introduces a new optional hook, RetrieveInstrumentationCustomScan,
to the CustomExecMethods struct. This hook allows custom scan providers to
implement logic to collect and consolidate instrumentation from shared
memory or worker states during the parallel query cleanup phase. This hook
is invoked via the new ExecCustomScanRetrieveInstrumentation function,
called from ExecParallelRetrieveInstrumentation for T_CustomScanState nodes.
Since the hook is optional (checked for NULL before calling), it maintains
full backward compatibility.

*Testing & Compatibility:*

   - The patch compiles and passes all core regression tests (make
   check-world) on my x86_64 instance.
   - The changes are not platform-specific.
   - Regression Tests: This patch provides a new *capability* for custom
   scan providers. Since the hook's functionality is only realized when
   implemented by an extension, specific tests would naturally reside within
   that extension rather than in the core regression suite.

This patch does not directly address a specific item on the official TODO
list but enhances the extensibility framework.

I believe this patch is complete and ready for review. I look forward to
any feedback and am happy to make revisions. I will also add this patch to
the next CommitFest.

Thank you,

Siddharth Kothari

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<div dir=3D"ltr"><div dir=3D"ltr"><div dir=3D"ltr"><p>Dear PostgreSQL Hacke=
rs,</p><p>This email proposes a patch to enhance the CustomScan provider in=
terface. The patch file,=C2=A0<code>0001-Add-RetrieveInstrumentationCustomS=
can-hook-for-Custo.patch</code>, is attached.</p><p><strong>Problem:</stron=
g></p><p>CustomScan providers currently lack a standard method to aggregate=
 instrumentation data from parallel workers back to the leader process befo=
re the Dynamic Shared Memory (DSM) segment is unlinked. This makes it diffi=
cult to gather comprehensive performance metrics from parallelized custom s=
cans.</p><p><strong>Solution:</strong></p><p>This patch introduces a new op=
tional hook,=C2=A0<code>RetrieveInstrumentationCustomScan</code>, to the=C2=
=A0<code>CustomExecMethods</code>=C2=A0struct. This hook allows custom scan=
 providers to implement logic to collect and consolidate instrumentation fr=
om shared memory or worker states during the parallel query cleanup phase. =
This hook is invoked via the new=C2=A0<code>ExecCustomScanRetrieveInstrumen=
tation</code>=C2=A0function, called from=C2=A0<code>ExecParallelRetrieveIns=
trumentation</code>=C2=A0for=C2=A0<code>T_CustomScanState</code>=C2=A0nodes=
. Since the hook is optional (checked for NULL before calling), it maintain=
s full backward compatibility.</p><p><strong>Testing &amp; Compatibility:</=
strong></p><ul><span style=3D"color:inherit"><li style=3D"margin-left:15px"=
>The patch compiles and passes all core regression tests (<code>make check-=
world</code>) on my x86_64 instance.</li></span><li style=3D"margin-left:15=
px">The changes are not platform-specific.</li><li style=3D"margin-left:15p=
x">Regression Tests:=C2=A0This patch provides a new=C2=A0<em>capability</em=
>=C2=A0for custom scan providers. Since the hook&#39;s functionality is onl=
y realized when implemented by an extension, specific tests would naturally=
 reside within that extension rather than in the core regression suite.</li=
></ul><p>This patch does not directly address a specific item on the offici=
al TODO list but enhances the extensibility framework.</p><span><p>I believ=
e this patch is complete and ready for review. I look forward to any feedba=
ck and am happy to make revisions. I will also add this patch to the next C=
ommitFest.</p><p>Thank you,</p><p>Siddharth Kothari</p></span></div>
</div>
</div>

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