Autovacuum - database

Does anyone know what autovacuum开发者_如何学Go means in the sense of databases?

Specific to PostgreSQL it means:

PostgreSQL's VACUUM command has to run on a regular basis for several reasons:

1.To recover or reuse disk space occupied by updated or deleted rows.

2.To update data statistics used by the PostgreSQL query planner.

3.To protect against loss of very old data due to transaction ID wraparound.

On Google App Engine this refers to the Indexes (you vacuum an index, meaning you remove it).

On Postgre it refers to tidying up the database table (garbage collection and optimisation).

An autovacuum daemon waits until there are no transactions and then dives in to perform the vacuum operation.

In postgres the AUTOVACUUM refers to regular maintenance tasks:

• To recover disk space occupied by updated or deleted rows.
• To update data statistics used by the PostgreSQL query planner.
• To protect against loss of very old data due to transaction ID wraparound.

See: http://www.postgresql.org/docs/8.1/static/maintenance.html