On Tue, 2008-10-28 at 08:49 +0000, Simon Riggs wrote: > Looking at a VACUUM's WAL records makes me think twice about the way we > issue a VACUUM. > > 1. First we scan the heap, issuing a HEAP2 clean record for every block > that needs cleaning.
IIRC the first heap pass just collects info and does nothing else. Is this just an empty/do-nothing WAL record ? > 2. Then we scan the index, issuing WAL records as appropriate. > > 3. Then we rescan the heap, issuing a HEAP2 clean record for every > block. > > I don't see a reason why we would issue 2 WAL records per block for a > VACUUM, nor why we would prune and remove in two steps, dirtying the > block each time. The first pass should just be collecting info and not dirtying anything. Could it be side effect of setting some transaction visibility bits on first visit ? In that case It would be good, if we could disable doing that that for vacuum. > Seems like we could write approximately half the amount > of data that we do. > > Surely we can come up with a better plan than that one? ------------------- Hannu Krosing http://www.2ndQuadrant.com PostgreSQL Scalability Training, Services and Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
