On Thu, Aug 21, 2014 at 7:19 PM, Eli Naeher <enae...@gmail.com> wrote: > However, when I try to do a > test self-join using it, Postgres does two seq scans across the whole table, > even though I have indexes on both id and previous_stop_event: > http://explain.depesz.com/s/ctck. Any idea why those indexes are not being > used?
Because the planner thinks seq scan+hash join is going to be faster than incurring the overhead of index scans for other kinds of plans. You can try out alternative plan types by running 'set enable_hashjoin=off' in your session. If it does turn out to be faster, then it usually means you haven't set planner tunables right (random_page_cost, effective_cache_size and possibly cpu_tuple_cost). Regards, Marti -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
