On Thu, Oct 11, 2012 at 8:55 PM, Korisk <kor...@yandex.ru> wrote: > hashes=# explain analyse verbose select name, count(name) as cnt from > hashcheck group by name order by name desc;
Now set enable_bitmapscan and enable_indexscan to on an try it again. Then set enable_seqscan to on and run it one more time. > > QUERY PLAN > > ------------------------------------------------------------------------------------------------------------------------------------------ > ------------------------------------------------ > GroupAggregate (cost=10000000000.00..10000596612.97 rows=200 width=32) > (actual time=0.136..7272.240 rows=4001 loops=1) > Output: name, count(name) > -> Index Only Scan using hashcheck_name_rev_idx on public.hashcheck > (cost=10000000000.00..10000466660.96 rows=25990002 width=32) (act > ual time=0.121..3624.624 rows=25990002 loops=1) > Output: name > Heap Fetches: 0 > Total runtime: 7272.735 ms > (6 rows) > > > > > > > 11.10.2012, 21:55, "Sergey Konoplev" <gray...@gmail.com>: >> On Thu, Oct 11, 2012 at 8:15 AM, Korisk <kor...@yandex.ru> wrote: >> >>> What's your seq_page_cost and random_page_cost? >>> hashes=# SELECT name, setting, reset_val FROM pg_settings WHERE setting <> >>> reset_val; >>> name | setting | reset_val >>> -------------------------+----------------+----------- >>> archive_command | (disabled) | >>> enable_bitmapscan | off | on >>> enable_indexscan | off | on >>> enable_seqscan | off | on >>> log_file_mode | 0600 | 384 >>> random_page_cost | 0.1 | 4 >>> seq_page_cost | 0.1 | 1 >>> transaction_isolation | read committed | default >>> unix_socket_permissions | 0777 | 511 >> >> Could you please try to set *_page_cost to 1 and then EXPLAIN ANALYZE it >> again? >> >>> -> Index Only Scan Backward using hashcheck_name_idx on >>> public.hashcheck >>> (cost=10000000000.00..10000398674.92 rows=25986792 width=32) >>> (actual time=0.104..3785.767 rows=25990002 loops=1) >> >> I am just guessing but it might probably be some kind of a precision >> bug, and I would like to check this. >> >>> (9 rows) >>> >>> Postgresql 9.2.1 was configured and built with default settings. >>> >>> Thank you. >> >> -- >> Sergey Konoplev >> >> a database and software architect >> http://www.linkedin.com/in/grayhemp >> >> Jabber: gray...@gmail.com Skype: gray-hemp Phone: +14158679984 -- Sergey Konoplev a database and software architect http://www.linkedin.com/in/grayhemp Jabber: gray...@gmail.com Skype: gray-hemp Phone: +14158679984 -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
