On Wed, Aug 16, 2017 at 1:40 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> I was wondering why the shm_toc code was using BUFFERALIGN and not
> MAXALIGN, and I now suspect that the answer is "it's an entirely
> undocumented kluge to make the atomics code not crash on 32-bit
> machines, so long as nobody puts a pg_atomic_uint64 anywhere except
> in a shm_toc".

Well, shm_toc considerably predates 64-bit atomics, so I think the
causality cannot run in that direction.  shm_toc.c first appeared in
the tree in January of 2014.  src/include/port/atomics didn't show up
until September of that year, and 64-bit atomics weren't actually
usable in practice until e8fdbd58fe564a29977f4331cd26f9697d76fc40 in
April of 2017.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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