Re: SIGSEGV in dynahash

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