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Re: NOLOGGING option, or ?

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alvaro Herrera <alvherre(at)surnet(dot)cl>,Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Greg Stark <gsstark(at)mit(dot)edu>,Neil Conway <neilc(at)samurai(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: NOLOGGING option, or ?
Date: 2005-06-01 20:17:39
Message-ID: 1117657059.3844.1042.camel@localhost.localdomain (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Wed, 2005-06-01 at 14:24 -0400, Tom Lane wrote:
> Alvaro Herrera <alvherre(at)surnet(dot)cl> writes:
> > On Wed, Jun 01, 2005 at 06:55:46PM +0100, Simon Riggs wrote:
> >> We're holding the table lock and will continue to do so until end of
> >> transaction. No transaction with an earlier id will ever see the data we
> >> load because of the lock.
> > Suppose you load half the tuples and the plug is pulled.  After
> > recovery, you have half-load of tuples that are visible to everyone.
> > This is a no-no.
> Simon is expecting that the loaded tuples are guaranteed to be erased
> (by table truncation) during recovery.  As I just noted I'm unconvinced
> of the safety of doing truncations during recovery, so I'd prefer not
> to depend on that.
> The scenario I was thinking of was different: you load pre-frozen
> tuples, commit, and thereby release the table lock.  Now the tuples
> are visible to transactions that started before you did; that's what
> violates MVCC.

Agreed. MVCC violation. OK, back to the drawing board.

Best Regards, Simon Riggs

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