Re: [PATCH] Add RetrieveInstrumentation hook for CustomScan providers

Hi everyone,

I’m just checking in to see if anyone has had a chance to look at this or
if there’s any further information I should provide to help with the
review. I have also added the patch to PG20-1 CF queue, the link is
https://commitfest.postgresql.org/patch/6524/.

Thanks,
Siddharth

On Wed, Feb 18, 2026 at 3:09 PM Siddharth Kothari <sidkot@google.com> wrote:

> 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
>