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Re: PgStat_HashKey padding issue when passed by reference

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Sami Imseih <samimseih@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-09-11T02:53:24Z
Lists: pgsql-hackers

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On Mon, Sep 08, 2025 at 09:36:52PM -0500, Sami Imseih wrote:
> But my concern is the flexibility of this approach. If someone is to add an
> OID field next, they will not be able to as that will be introducing
> padding.  On the other hand, passing the key by reference and
> documenting the reason in pgstat_shmem.c will not lose this
> flexibility.

I don't mind discarding the static assertion idea, but at the end what
counts for me here is that I don't want to sacrifice future changes in
the pgstats code that would always require passing around the hash key
by reference.  So I would just do like attached, documenting at the
top of PgStat_HashKey that we should not have padding in it, removing
three memset(0) calls that expected it.
--
Michael

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Document and check that PgStat_HashKey has no padding