I noticed something strange today, and thought I should report it. I vacuumed a database, and as expected, one of the table's size decreased (other table were VACUUMed individually earlier); but o my astonishment, the size of the UNIQUE KEY index on one of the columns increased.
That's normal. VACUUM FULL creates new index pointers for the tuples it moves, which can lead to a bigger index. If it bothers, REINDEX will pack the indexes tighter again.
That explains it... and yes, REINDEX did bring the index size back to normal.
Would it make sense to mention this in docs of VACUUM FULL? Either at
