| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, jd(at)commandprompt(dot)com, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Prepared transactions vs novice DBAs, again |
| Date: | 2009-04-23 03:04:41 |
| Message-ID: | 13294.1240455881@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Maybe I'm just dumb, but I don't get it. If I start a transaction and
> do "SELECT * FROM foo" and then wait around for an hour or two while
> someone else makes changes to foo and then do "SELECT * FROM foo"
> again, I expect to see the same rows I saw the first time, which means
> they still need to be around.
That only happens in a serializable transaction, ie, one that took
*and kept* a snapshot at transaction start. In READ COMMITTED mode
we drop all snaps between statements, so there is nothing stopping
reclaiming of rows that were visible to prior statements.
regards, tom lane
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