| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Kevin Grittner <kgrittn(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)postgresql(dot)org>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, "pgsql-committers(at)postgresql(dot)org" <pgsql-committers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold < |
| Date: | 2016-05-24 18:11:44 |
| Message-ID: | 20160524181144.GA441079@alvherre.pgsql |
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| Lists: | pgsql-committers pgsql-hackers |
Kevin Grittner wrote:
> On Tue, May 24, 2016 at 12:00 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> > Analyze IIRC acquires a new snapshot when getting sample rows,
>
> I could not find anything like that, and a case-insensitive search
> of analyze.c finds no occurrences of "snap". Can you remember
> where you think you saw something that would cause the ANALYZE
> command in my test to use a snapshot other than the one from the
> REPEATABLE READ transaction in which it was run?
For ANALYZE, the snapshot is set in vacuum() prior to calling
analyze_rel(); see vacuum.c.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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