Database Reference
In-Depth Information
Version 9.2 introduced index-only scans, which made compound indexes even more
relevant because the planner can just scan the index and use data from the index without
ever needing to check the underlying table. So if you commonly filter by the same set
of fields and output those, a compound index should improve speed. Keep in mind that
the more columns you have in an index, the fatter your index and the less of it that can
easily fit in RAM. Don't go overboard with compound indexes.
