On Sun, Aug 21, 2005 at 09:50:10PM -0400, Tom Lane wrote: > Satoshi Nagayasu <[EMAIL PROTECTED]> writes: > > I've done a quick hack to implement PCTFREE on PostgreSQL. > > ... > > According to my experiments, pgbench score was improved 10% or more > > with 1024 bytes free space. > > I'm not very enthused about this. Enforcing 12.5% PCTFREE means that > you pay 12.5% extra I/O costs across the board for INSERT and SELECT > and then hope you can make it back (plus some more) on UPDATEs. > pgbench is a completely UPDATE-dominated benchmark and thus it makes > such a patch look much better than it would on other workloads. > > I think the reason Oracle offers this has to do with their > overwrite-based storage management; it's not obvious that the tradeoff > is as useful for us. There are some relevant threads in our archives > here, here, and here: > http://archives.postgresql.org/pgsql-patches/2005-04/msg00078.php > http://archives.postgresql.org/pgsql-performance/2004-08/msg00402.php > http://archives.postgresql.org/pgsql-performance/2003-10/msg00618.php
It should be possible to see what the crossover point is in terms of benefit using dbt2 and tweaking the transactions that are run, something I can do if there's interest. But I agree with Satoshi; if there are people who will benefit from this option (which doesn't hurt those who choose not to use it), why not put it in? -- Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED] Pervasive Software http://pervasive.com 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
