PostgreSQL 10 Administration Cookbook - Fourth Edition

Table and index bloat

Table bloat is something that can develop over time if some maintenance processes can't be run properly. In other words, due to the way Multiversion Concurrency Control (MVCC) works, your table will contain a lot of older versions of rows, if these versions can't be removed in a timely manner.

There are several ways this can develop, but all involve lots of updates or deletes and inserts, while autovacuum is prevented from doing its job of getting rid of old tuples. It is possible that, even after the old versions are deleted, the table stays at its newly acquired and large size, thanks to visible rows being located at the end of the table and preventing PostgreSQL from shrinking the file. There have been cases where ...