Re: problem with pg_statistics
От | Andre Schubert |
---|---|
Тема | Re: problem with pg_statistics |
Дата | |
Msg-id | 20030627081306.71ffbb2e.andre.schubert@km3.de обсуждение исходный текст |
Ответ на | Re: problem with pg_statistics (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-performance |
On Thu, 26 Jun 2003 12:03:52 -0400 Tom Lane <tgl@sss.pgh.pa.us> wrote: > Manfred Koizar <mkoi-pg@aon.at> writes: > > On Thu, 26 Jun 2003 10:08:05 -0400, Tom Lane <tgl@sss.pgh.pa.us> > > wrote: > >> Try reducing random_page_cost > > > With index scan cost being more than 25 * seq scan cost, I guess that > > - all other things held equal - even random_page_cost = 1 wouldn't > > help. > > Oh, you're right, I was comparing the wrong estimated costs. Yeah, > changing random_page_cost won't fix it. > > > Or there's something wrong with correlation? > > That seems like a good bet. Andre, is this table likely to be > physically ordered by time_stamp, or nearly so? If so, do you > expect that condition to persist, or is it just an artifact of > a test setup? > Sorry forgot the pg_stat query... SELECT * FROM pg_stats where tablename = 'tbl_traffic' and attname = 'time_stamp'; tablename | attname | null_frac | avg_width | n_distinct | most_common_vals | most_common_freqs | histogram_bounds | correlation -------------+------------+-----------+-----------+------------+------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------+--------------------------------------------------------------------+--------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------------+------------- tbl_traffic | time_stamp | 0 | 8 | 104009 | {"2003-06-03 19:12:01.059625+02","2003-02-03 19:52:06.666296+01","2003-02-1309:59:45.415763+01","2003 -02-28 18:10:28.536399+01","2003-04-11 18:09:42.30363+02","2003-04-26 20:35:50.110235+02","2003-05-03 11:09:32.991507+02","2003-05-2009:53:51.271853+02","2003-05-21 2 0:55:59.155387+02","2003-06-02 02:38:28.823182+02"} | {0.00133333,0.001,0.001,0.001,0.001,0.001,0.001,0.001,0.001,0.001}| {"2002-07-01 00:00:00+02","2003-02-21 01:59: 46.107696+01","2003-03-11 15:00:37.418521+01","2003-03-26 18:14:50.028972+01","2003-04-10 13:43:20.75909+02","2003-04-2709:03:19.592213+02","2003-05-08 22:35:41.99761 6+02","2003-05-22 15:34:42.932958+02","2003-06-03 00:53:05.870782+02","2003-06-15 08:45:41.154875+02","2003-06-27 07:18:30.265868+02"}| -0.479749 (1 row) Thanks, as
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