| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ALTER TABLE lock strength reduction patch is unsafe |
| Date: | 2012-01-03 18:33:42 |
| Message-ID: | CA+TgmoaNehGhOTVc58bXLE0aL2efnNhDFS7-JyeVFhwPo3UQ8Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jan 3, 2012 at 1:24 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Um ... you're supposing that only DDL uses SnapshotNow, which is wrong.
> I refer you to the parser, the planner, execution functions for arrays,
> records, enums, any sort of relcache reload, etc etc etc. Yes, some
> of that is masked by backend-internal caching, some of the time, but
> it's folly to just assume that there are no SnapshotNow scans during
> normal queries.
Hmm. That's unfortunate, because it seems difficult to construct a
test case that will exercise every feature in the system.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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