| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> |
| Subject: | Re: Atomics for heap_parallelscan_nextpage() |
| Date: | 2017-08-16 17:47:23 |
| Message-ID: | CA+Tgmob4zSzZ0bx-34Dqbsc62gsvVEFGpF57ovN8NbAZG5FdRw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Aug 16, 2017 at 1:40 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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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