PostgreSQL's VACUUM command has to process each table on a regular basis for several reasons:
Each of these reasons dictates performing VACUUM operations of varying frequency and scope,
* To recover or reuse disk space occupied by updated or deleted rows. * To update data statistics used by the PostgreSQL query planner. * To update the visibility map, which speeds up index-only scans. * To protect against loss of very old data due to transaction ID wraparound or multixact ID wraparound.
Each of these reasons dictates performing VACUUM operations of varying frequency and scope,
Further explaination can be found together with the syntax schema for VACUUM:
VACUUM reclaims storage occupied by dead 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.
Vacuum a specific table in verbose mode:
psql mydb You are now connected to database "mydb" as user "postgres".
vacuum (verbose, analyze) myschema.mytable;
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