"VACUUM reclaims storage occupied by deleted tuples. In normal PostgreSQL operation, tuples that are deleted or obsoleted by an update are not physically removed from their table; they remain present until a VACUUM is done. Therefore it's necessary to do VACUUM periodically, especially on frequently-updated tables."
"The "vacuum analyze" form additionally collects statistics on the disbursion of columns in the database, which the optimizer uses when it calculates just how to execute queries. The availability of this data can make a tremendous difference in the execution speed of queries. This command can also be run from cron, but it probably makes more sense to run this command as part of your nightly backup procedure - if "vacuum" is going to screw up the database, you'd prefer it to happen immediately after (not before!) you've made a backup! The "vacuum" command is very reliable, but conservatism is the key to good system management. So, if you're using the export procedure described above, you don't need to do this extra step".
All its tables constantly manipulated (INSERT, UPDATE, DELETE) they need a VACUUM, therefore the necessity to execute at least one time to the day normally of dawn if its database will be very great .
[],s
Marcelo Costa Secretaria Executiva de Educação do Pará Amazonia - Pará - Brazil
Are there guidelines (or any empirical data) available how to determine how often a table should be vacuumed for optimum performance or is this an experience / trial-and-error thing?
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