| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Noah Misch <noah(at)leadboat(dot)com> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Atri Sharma <atri(dot)jiit(at)gmail(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ALTER TABLE lock strength reduction patch is unsafe Reply-To: |
| Date: | 2014-03-06 23:49:16 |
| Message-ID: | CA+U5nMKrnGPBn-0kiXZvMkSUPSRjBZjFjuMPr-t1_CTCFLEQ1w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 6 March 2014 22:43, Noah Misch <noah(at)leadboat(dot)com> wrote:
> Good analysis. The hazards arise when pg_dump uses one of the ruleutils.c
> deparse worker functions.
Ah, good. We're thinking along the same lines. I was already working
on this analysis also. I'll complete mine and then compare notes.
> One thing not to forget is that you can always get the old mutual exclusion
> back by issuing LOCK TABLE just before a DDL operation. If some unlucky user
> regularly gets pg_dump failures due to concurrent DROP TRIGGER, he has a
> workaround. There's no comparable way for someone who would not experience
> that problem to weaken the now-hardcoded AccessExclusiveLock.
Good point.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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