| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: ALTER TABLE SET STATISTICS requires AccessExclusiveLock |
| Date: | 2010-07-18 17:20:25 |
| Message-ID: | 12734.1279473625@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> On Sunday 18 July 2010 18:02:26 Simon Riggs wrote:
>> Then I think the fix is to look at the xmin values on all of the tables
>> used during planning and ensure that we only use constraint-based
>> optimisations in a serializable transaction when our top xmin is later
>> than the last DDL change (via its xmin).
> Why not just use a the normal snapshot at that point?
There isn't a "normal snapshot" that the planner should be relying on.
It doesn't know what snap the resulting plan will be used with.
I'm unconvinced that this is a problem worth worrying about, but if it
is then Simon's probably got the right idea: check the xmin of a
pg_constraint row before depending on it for planning. Compare the
handling of indexes made with CREATE INDEX CONCURRENTLY.
regards, tom lane
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