From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Commits 8de72b and 5457a1 (COPY FREEZE) |
Date: | 2012-12-05 23:47:38 |
Message-ID: | CA+TgmoZp5EQJd_865Pr6OTOf5boS9Y1=-UY+AmgRg5FMCdXLTQ@mail.gmail.com |
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Lists: | pgsql-hackers |
On Tue, Dec 4, 2012 at 3:38 PM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> After reading that thread, I still don't understand why it's unsafe to
> set HEAP_XMIN_COMMITTED in those conditions. Even if it is, I would
> think that a sufficiently narrow case -- such as CTAS outside of a
> transaction block -- would be safe, along with some slightly broader
> cases (like BEGIN; CREATE TABLE; INSERT/COPY).
I haven't looked at the committed patch - which seemed a bit
precipitous to me given the stage the discussion was at - but I
believe the general issue with HEAP_XMIN_COMMITTED is that there might
be other snapshots in the same transaction, for example from open
cursors.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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