Re: ALTER TABLE lock strength reduction patch is unsafe

Robert Haas <robertmhaas@gmail.com>

From: Robert Haas <robertmhaas@gmail.com>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: Simon Riggs <simon@2ndquadrant.com>, pgsql-hackers@postgresql.org

Date: 2011-06-17T22:34:49Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Add bytea_agg, parallel to string_agg.
- d5448c7d31b5 9.2.0 cited
Fix ALTER TABLE ONLY .. DROP CONSTRAINT.
- c0f03aae0469 9.2.0 cited

On Thu, Jun 16, 2011 at 6:54 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 4. Backend #2 visits the new, about-to-be-committed version of
> pgbench_accounts' pg_class row just before backend #3 commits.
> It sees the row as not good and keeps scanning.  By the time it
> reaches the previous version of the row, however, backend #3
> *has* committed.  So that version isn't good according to SnapshotNow
> either.

<thinks some more>

Why isn't this a danger for every pg_class update?  For example, it
would seem that if VACUUM updates relpages/reltuples, it would be
prone to this same hazard.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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