| 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 17:49:42 |
| Message-ID: | CA+TgmoZnDvR73Cmps+3V9Pm+FSJpEUV618hVQXBLQ-XJKCYKGA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Aug 16, 2017 at 1:44 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I was feeling a bit uncomfortable with the BUFFERALIGN_DOWN() for a
> different reason: if the caller has specified the exact amount of space it
> needs, having shm_toc_create discard some could lead to an unexpected
> failure.
Well, that's why Heikki also patched shm_toc_estimate. With the
patch, if the size being used in shm_toc_create comes from
shm_toc_estimate, it will always be aligned and nothing bad will
happen. If the user invents another size out of whole cloth, then
they might get a few bytes less than they expect, but that's what you
get for not using shm_toc_estimate().
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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