PostgreSQL

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table The name of a specific table to vacuum. Defaults to all tables. column The name of a specific column to analyze. Defaults to all columns.


Outputs


VACUUM The command has been accepted and the database is being cleaned.


NOTICE: -Relation table — The report header for table.


NOTICE: Pages 98: Changed 25, Reapped 74, Empty 0, New 0; Tup 1000: Vac3000, Crash 0, UnUsed 0, MinLen 188, MaxLen 188; Re-using: Free/AvaiL Space 586952/586952; EndEmpty/AvaiL Pages 0/74. Elapsed 0/0 sec. The analysis for table itself.


NOTICE: Index index : Pages 28; Tuples 1000: Deleted 3000. Elapsed 0/0 sec. Theanaly-sis for an index on the target table.


Deseription


VACUUM serves two purposes in Postgres as both a means to reclaim storage and also a means to collect information for the optimizer.


VACUUM opens every class in the database, cleans out records from rolled back transactions, and updates statistics in the system catalogs. The statistics maintained include the number of tuples and number of pages stored in all classes.


VACUUM ANALYZE collects statistics representing the dispersion of the data in each column. This information is valuable when several query execution paths are possible.


Running VACUUM periodically will increase the speed of the database in processing user queries.


Notes


The open database is the target for VACUUM.


We recommend that active production databases be VACUUM-ed nightly, in order to remove expired rows. After copying a large class into Postgres or after deleting a large number of records, it may be a good idea to issue a VACUUM ANALYZE query. This will update the system catalogs with the results of all recent changes, and allow the Postgres query optimizer to make better choices in planning user queries.

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