COPY with no WAL, in certain circumstances

http://archives.postgresql.org/pgsql-hackers/2006-10/msg01172.php

As discussed on -hackers, its possible to avoid writing any WAL at all
for COPY in these circumstances:

BEGIN;
  CREATE TABLE foo..
  COPY foo...
COMMIT;

BEGIN;
  TRUNCATE foo..
  COPY foo...
COMMIT;

The enclosed patch implements this, as discussed. There is no user
interface to enable/disable, just as with CTAS and CREATE INDEX; no
docs, just code comments.

This plays nicely with the --single-transaction option in psql to allow
fast restores/upgrades.

YMMV but disk bound COPY will benefit greatly from this patch, some
tests showing 100% gain. COPY is still *very* CPU intensive, so some
tests have shown negligible benefit, fyi, but that isn't the typical
case.

Applies cleanly to CVS HEAD, passes make check.

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