| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)surnet(dot)cl> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, 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 18:24:39 |
| Message-ID: | 17405.1117650279@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
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.
regards, tom lane
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