From: Michael Paquier <michael@paquier.xyz>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Konstantin Knizhnik <knizhnik@garret.ru>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Subject: Re: SIGSEGV in dynahash
Date: Sun, 16 Aug 2026 08:32:16 +0900
Message-ID: <aoD3ACTRYXaF7t1-@paquier.xyz> (raw)
In-Reply-To: <16448.1786810349@sss.pgh.pa.us>
References: <d59221f2-b3d2-41ad-8bf0-d581b42e4cba@garret.ru>
<16448.1786810349@sss.pgh.pa.us>
On Sat, Aug 15, 2026 at 12:12:29PM -0400, Tom Lane wrote:
> Yeah. I'm not too pleased with 9fe9ecd516b for a different reason.
>
> In pursuit of what seems to be a merely cosmetic goal (ie make shared
> hashes be reported differently in pg_shmem_allocations), it's made a
> fundamental and IMO possibly destabilizing change in the behavior of
> shared-memory hash tables. To wit, it is no longer possible to expand
> a shared hash table beyond its startup-time allocation.
There is a difference between shmem_hash.c and dynahash.c. dynahash.c
is able to support a growing size, but it's not the case of
shmem_hash.c.
Note also some comments in dynahash.c:
* table grows much beyond the initial size. (Currently, shared memory hash
* tables are only created by ShmemRequestHash()/ShmemInitHash() though, which
* doesn't support growing at all.)
shmem_hash_create() also claims the non-growth argument as true as we
would need to grow the underlying shmem region linked with a hash
table defined by shmem_hash.c.
Or am I missing something?
--
Michael
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Cc: michael@paquier.xyz, tgl@sss.pgh.pa.us, knizhnik@garret.ru, hlinnaka@iki.fi, pgsql-bugs@lists.postgresql.org
Subject: Re: SIGSEGV in dynahash
In-Reply-To: <aoD3ACTRYXaF7t1-@paquier.xyz>
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