On Fri, May 11, 2007 at 01:25:04PM -0400, Alvaro Herrera wrote: > Guillaume Cottenceau wrote: > > Guillaume Cottenceau <gc 'at' mnc.ch> writes: > > > > > With that in mind, I've tried to estimate how much benefit would > > > be brought by running VACUUM FULL, with the output of VACUUM > > > VERBOSE. However, it seems that for example the "removable rows" > > > reported by each VACUUM VERBOSE run is actually reused by VACUUM, > > > so is not what I'm looking for. > > > > I've tried to better understand how autovacuum works (we use 7.4) > > to see if a similar mechanism could be used in 7.4 (e.g. run > > VACUUM ANALYZE often enough to not end up with a need to VACUUM > > FULL). > > > > The autovacuum daemon uses statistics collected thanks to > > stats_row_level. However, inside pg_stat_user_tables, the values > > n_tup_upd and n_tup_del seem to be reported from pg startup and > > never reset, whereas the information from previous VACUUM would > > be needed here, if I understand correctly. Is there anything that > > can be done from that point on with existing pg information, or > > I'd need e.g. to remember the values of my last VACUUM myself? > > In 7.4 there was the pg_autovacuum daemon in contrib, wasn't there? No > need to write one yourself.
Correct. But one important note: the default parameters in the 7.4 contrib autovac are *horrible*. They will let your table grow to 3x minimum size, instead of 1.4x in 8.0/8.1 and 1.2x in 8.2. You must specify a different scale if you want anything resembling good results. -- Jim Nasby [EMAIL PROTECTED] EnterpriseDB http://enterprisedb.com 512.569.9461 (cell) ---------------------------(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
