One of the most important things that PostgreSQL users and administrators need to understand is VACUUM.  VACUUM is used to collect statistics, to mark tuples (rows) as deleted, and to reclaim disk space.  But what does VACUUM really do?  How does it work?  And what’s the difference between plain ol’ VACUUM and VACUUM FULL?  This talk, by PostgreSQL veteran Simon Riggs, introduces VACUUM, and describes what you should (and shouldn’t) expect it to do.