Claudio Freire <klaussfreire@xxxxxxxxx> writes: > On Wed, Aug 7, 2013 at 3:34 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: >> Note that there's no particular need to specify "desc" in the index >> definition. This same index can support searches in either direction >> on the "called" column. > Yeah, but it's faster if it's in the same direction, because the > kernel read-ahead code detects sequential reads, whereas it doesn't > when it goes backwards. The difference can be up to a factor of 10 for > long index scans. Color me skeptical. Index searches are seldom purely sequential block accesses. Maybe if you had a freshly built index that'd never yet suffered any inserts/updates, but in practice any advantage would disappear very quickly after a few index page splits. > Though... true... for a limit 1... it wouldn't matter that much. That's the other point. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
