Re: Commits 8de72b and 5457a1 (COPY FREEZE)

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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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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