From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Fix crash on trying to expand a shared memory hash table
Date: Tue, 25 Aug 2026 11:12:52 +0000
Message-ID: <E1wyp5H-0000000237T-11CX@gemulon.postgresql.org> (raw)
Fix crash on trying to expand a shared memory hash table
When a hash table grows large enough we try to expand the directory,
but we shouldn't try to do that if the hash table is marked as
HASH_FIXED_SIZE. Before commit 9fe9ecd516b that was harmless,
although it was a little weird to expand the directory when allocating
the new element was doomed to fail later anyway. But the new
allocator function added in that commit for shared memory hash tables
did not expect to be called after hash table creation at all and would
just crash. Fix by ensuring that the allocator is not called after
hash table creation for HASH_FIXED_SIZE tables.
The crash started with commit 9fe9ecd516b in v19, so backpatch to v19.
To trigger the crash, you needed a shared memory hash table of just
the right size so that we would attempt to resize it: power-of-2 and
at least HASH_SEGSIZE (256) elements. With any other size, you would
run out of allocated elements first.
Author: Konstantin Knizhnik <knizhnik@garret.ru>
Reviewed-by: Rahila Syed <rahilasyed90@gmail.com>
Discussion: https://www.postgresql.org/message-id/d59221f2-b3d2-41ad-8bf0-d581b42e4cba@garret.ru
Backpatch-through: 19
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/86481d9f4930750a9c62c25216bf7783f69d6ff0
Modified Files
--------------
src/backend/utils/hash/dynahash.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
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To: pgsql-committers@postgresql.org
Cc: heikki.linnakangas@iki.fi, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Fix crash on trying to expand a shared memory hash table
In-Reply-To: <E1wyp5H-0000000237T-11CX@gemulon.postgresql.org>
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