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Re: Idea for getting rid of VACUUM FREEZE on cold pages

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: Josh Berkus <josh(at)agliodbs(dot)com>, Jesper Krogh <jesper(at)krogh(dot)cc>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Idea for getting rid of VACUUM FREEZE on cold pages
Date: 2010-05-27 19:39:47
Message-ID: AANLkTimy4hDyTqbrsi2XIXDklRRJkcA55myaxL5EZrAc@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, May 27, 2010 at 3:15 PM, Kevin Grittner
<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> Jesper Krogh <jesper(at)krogh(dot)cc> wrote:
>
>> Couldn't pages that are totally filled by the same transaction, be
>
>> frozen on the initial write?
>
> As far as I'm aware, that can only be done if:
>
> (a)  The tuples were written within the same transaction which
> created or truncated the table.
>
> *or*
>
> (b)  The writing transaction and all transactions concurrent to it
> have completed by the time the page is about to be written.

Actually, I think this is true only in case (b).  In case (a), you
mess up visibility with respect to other command-IDs within the
transaction.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company

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