From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
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To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: ALTER TABLE lock strength reduction patch is unsafe |
Date: | 2011-06-17 19:15:34 |
Message-ID: | BANLkTi=0uPvo1B1yGVKEEg2J+g-7L124RA@mail.gmail.com |
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Lists: | pgsql-hackers |
On Fri, Jun 17, 2011 at 3:08 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> Not so. The extra locking would only occur on the first lock
> acquisition after DDL operations occur. If that was common then your
> other performance patch would not be an effective optimisation. There
> is no additional locking from what I've proposed in the common code
> path - that's why we have a relcache.
The extra locking would also occur when *initially* building relcache
entries. In other words, this would increase - likely quite
significantly - the overhead of backend startup. It's not going to be
sufficient to do this just for pg_class; I think you'll have to do it
for pg_attribute, pg_attrdef, pg_constraint, pg_index, pg_trigger,
pg_rewrite, and maybe a few others I'm not thinking of right now.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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