Re: COPY with no WAL, in certain circumstances

On Sat, 2007-01-06 at 21:32 -0500, Tom Lane wrote:
> Robert Treat <xzilla(at)users(dot)sourceforge(dot)net> writes:
> > On Saturday 06 January 2007 16:36, Simon Riggs wrote:
> > <snip>
> >> BEGIN;
> >> CREATE TABLE foo...
> >> INSERT INTO foo --uses WAL
> >> COPY foo.. --no WAL
> >> INSERT INTO foo --uses WAL
> >> COPY foo.. --no WAL
> >> INSERT INTO foo --uses WAL
> >> COPY foo... --no WAL
> >> COMMIT;
>
> > Is there some technical reason that the INSERT statements need to use WAL in
> > these scenarios?
>
> First, there's enough other overhead to an INSERT that you'd not save
> much percentagewise. Second, not using WAL doesn't come for free: the
> cost is having to fsync the whole table afterwards. So it really only
> makes sense for commands that one can expect are writing pretty much
> all of the table. I could easily see it being a net loss for individual
> INSERTs.

Agreed. We agreed that before, on the original design thread.

--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com