Csaba Nagy wrote: > On Fri, 2007-09-21 at 10:43 +0100, Gregory Stark wrote: >> The other possibility is that Postgres just hasn't even touched a large part >> of its shared buffers. > > But then how do you explain the example I gave, with a 5.5GB table > seq-scanned 3 times, shared buffers set to 12 GB, and top still showing > almost 100% memory as cached and no SWAP "used" ? In this case you can't > say postgres didn't touch it's shared buffers - or a sequential scan > won't use the shared buffers ?
Which version of Postgres is this? In 8.3, a scan like that really won't suck it all into the shared buffer cache. For seq scans on tables larger than shared_buffers/4, it switches to the bulk read strategy, using only a few buffers, and choosing the starting point with the scan synchronization facility. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
