On Tue, 2008-10-28 at 16:22 +0200, Heikki Linnakangas wrote: > Arbitrarily, if after a > heap insert/update there's less than 20% of free space on the page, > the FSM is updated. Compared to updating it every time, that saves a > lot of overhead, while doing a pretty good job at marking full pages > as full in the FSM. My first thought was to update the FSM if there > isn't enough room on the page for a new tuple of the same size as the > one just > inserted; that would be pretty close to the logic we have during > normal > operation, where the FSM is updated when the tuple that we're about > to > insert doesn't fit on the page. But because we don't know the > fillfactor > during recovery, I don't think we can do reliably.
With HOT, we tend to hover around the nearly-full state, so this seems like it will trigger repeatedly. Is it possible that we could put an extra field onto a heap_clean record to show remaining space. We would use it only for VACUUMs, not HOT, just as we do now. Probably good idea to make a list of user cases and say what we do in eahc case. e.g. COPY, other bulk ops, HOT etc.. I wonder if there is merit in having an XLogInsertMulti() which inserts multiple records in a batch as a way of reducing WALInsertLock traffic. It might be possible to piggyback FSM records onto the main heap changes. -- Simon Riggs www.2ndQuadrant.com PostgreSQL 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