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Re: NOLOGGING option, or ?

From: Alvaro Herrera <alvherre(at)surnet(dot)cl>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,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 18:10:45
Message-ID: 20050601181045.GA26471@surnet.cl (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Jun 01, 2005 at 06:55:46PM +0100, Simon Riggs wrote:
> On Wed, 2005-06-01 at 11:55 -0400, Tom Lane wrote:
> > Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> > > 4. Optionally, we set a flag on the table showing the whole table is
> > > frozen. Anybody writing to this table subsequently will spoil this flag.
> > > If the flag is set, all forms of VACUUM will return success immediately
> > > without performing a scan (since it is already in a perfect VACUUM FULL
> > > and VACUUM FREEZE state).
> > 
> > This bit strikes me as dangerous and not related to the original
> > proposal.  I don't care for the load-already-frozen-data part at all,
> > either.  That's not just giving up WAL protection, that's an outright
> > MVCC semantics violation, in return for which we get ... not much.
> > Certainly not any speedup in the LOAD itself.
> 
> I agree it *sounds* dangerous, but is it? If so, how? I will immediately
> withdraw any idea that proves dangerous.
> 
> 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.  Plus, what is the benefit of having the tuples in
frozen state to start with?  If this is a data warehouse application,
I'd expect the table to be dropped or truncated rather before the
billion-transactions barrier comes to pass.

-- 
Alvaro Herrera (<alvherre[a]surnet.cl>)
"I dream about dreams about dreams", sang the nightingale
under the pale moon (Sandman)

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