Horton

Re: Proposal: Add a callback data parameter to GetNamedDSMSegment

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Sami Imseih <samimseih@gmail.com>
Cc: Zsolt Parragi <zsolt.parragi@percona.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-12-03T20:07:56Z
Lists: pgsql-hackers

Commits

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

  1. Allow passing a pointer to GetNamedDSMSegment()'s init callback.

  2. Move dynamically-allocated LWLock tranche names to shared memory.

On Wed, Dec 03, 2025 at 12:47:46PM -0600, Sami Imseih wrote:
> Can you provide more details on the use-case?

I think the main use-case is creating multiple DSM segments in the registry
that use the same initialization callback.  I ran into this when I was
working on GetNamedDSA() and GetNamedDSHash().  In early versions of the
patch, the new functions used GetNamedDSMSegment() to allocate the space
for all the DSA/dshash information [0].  Since initializing those segments
required the user-provided name string, I ended up taking a lock after
calling GetNamedDSMSegment() and doing most of the initialization there.
My gut feeling is that this is an obscure enough use-case that this
workaround is probably sufficient, but I am interested to hear more...

[0] https://postgr.es/m/attachment/177621/v8-0001-simplify-creating-hash-table-in-dsm-registry.patch

-- 
nathan