Actually I'd like to add something to this. I think I've found a bug in the current implementation. Would someone be able to check?
Given a table definition of (market text, feedcode text, updated_at timestamptz, value float8) and an index on (market, feedcode, updated_at desc) (note that this table slightly deviates from what I described in my previous mail) and filling it with data. The following query uses an index skip scan and returns just 1 row (incorrect!) select distinct on (market, feedcode) market, feedcode from streams.base_price where market='TEST' The following query still uses the regular index scan and returns many more rows (correct) select distinct on (market, feedcode) * from streams.base_price where market='TEST' It seems that partially filtering on one of the distinct columns triggers incorrect behavior where too many rows in the index are skipped. -Floris
