Anton Melser wrote: > On 09/11/06, Alvaro Herrera <alvherre@xxxxxxxxxxxxxxxxx> wrote: > >Anton Melser wrote: > > > >> Thanks for that. Just a clarification, can someone tell me what the > >> "number of tuples" means in the context of the multipliers? I mean, > >> when the vacuum min multiplier is at 0.4, we multiply 0.4 by what? I > >> get the min val, but what are we multiplying by 0.4? The total number > >> of tuples in the table? The total modified/deleted? > > > >pg_class.reltuples > > So I am still a little unclear... I need to analyse to get relevant > stats for autovacuum... but autovacuum needs to be used to update the > relevant stats? Can I REALLY do without a cronjob, or am I just > thinking wishfully (I can invent expressions if I want!). This means that we use the previously-known value of tuples in the table, plus the number of new tuples that have been inserted, deleted and/or updated (numbers you can see in the pg_stat_* views), and compare them to the thresholds. If I'm being too unclear, here is the relevant code comment: * A table needs to be vacuumed if the number of dead tuples exceeds a * threshold. This threshold is calculated as * * threshold = vac_base_thresh + vac_scale_factor * reltuples * * For analyze, the analysis done is that the number of tuples inserted, * deleted and updated since the last analyze exceeds a threshold calculated * in the same fashion as above. Note that the collector actually stores * the number of tuples (both live and dead) that there were as of the last * analyze. This is asymmetric to the VACUUM case. (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/autovacuum.c?rev=1.28;content-type=text%2Fx-cvsweb-markup) The idea is that you _can_ do without a cronjob. You may need to do a first ANALYZE just to get things warmed up, and then let autovacuum do its job. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.
