a lot of shared buffers hit when planning for a simple query with primary access path
Hi, a simple SQL "select ... from tablex where id1=34215670 and id2=59403938282; id1 and i2 are bigint and primary key. Index Cond: ((tablex.id2 = ' 5940393828299'::bigint) AND (tablex.id1 = ' 34215670 '::bigint)) Buffers: shared hit=2 Query Identifier: -1350604566224020319 Planning: Buffers: shared hit=110246 <<< here planning need access a lot of buffers Planning Time: 81.850 ms Execution Time: 0.034 ms could you help why planning need a lot of shared buffers access ? this table has 4 indexes. and I tested similar SQL with another table has 4 compound indexes and that table only show very small shared buffers hit when planning. this table has a lot of "update" and "delete" . Thanks, James
Re: a lot of shared buffers hit when planning for a simple query with primary access path
On Mon, 1 Jul 2024 at 21:45, James Pang wrote: >Buffers: shared hit=110246 <<< here planning need access a lot of > buffers > Planning Time: 81.850 ms > Execution Time: 0.034 ms > >could you help why planning need a lot of shared buffers access ? Perhaps you have lots of bloat in your system catalogue tables. That could happen if you make heavy use of temporary tables. There are many other reasons too. It's maybe worth doing some vacuum work on the catalogue tables. David
Re: a lot of shared buffers hit when planning for a simple query with primary access path
Hi po 1. 7. 2024 v 12:10 odesílatel David Rowley napsal: > On Mon, 1 Jul 2024 at 21:45, James Pang wrote: > >Buffers: shared hit=110246 <<< here planning need access a > lot of buffers > > Planning Time: 81.850 ms > > Execution Time: 0.034 ms > > > >could you help why planning need a lot of shared buffers access ? > > Perhaps you have lots of bloat in your system catalogue tables. That > could happen if you make heavy use of temporary tables. There are many > other reasons too. It's maybe worth doing some vacuum work on the > catalogue tables. > The planners get min/max range from indexes. So some user's indexes can be bloated too with similar effect Regards Pavel > David > > >
Re: a lot of shared buffers hit when planning for a simple query with primary access path
On Mon, 1 Jul 2024 at 22:20, Pavel Stehule wrote: > The planners get min/max range from indexes. So some user's indexes can be > bloated too with similar effect I considered that, but it doesn't apply to this query as there are no range quals. David
Re: a lot of shared buffers hit when planning for a simple query with primary access path
we have a daily job to do vacuumdb including catalog tables, and in same database , I did similar query with where=pk on another table and shared buffer access is very small, if catalog table bloat, should see similar shared buffer access when planning for other tables ,right? How to get more details about this planning ? relname | last_vacuum | last_analyze -+---+--- pg_statistic| 2024-06-30 01:13:08.703291+00 | pg_attribute| 2024-06-30 01:14:48.061235+00 | 2024-07-01 01:11:49.377759+00 pg_class| 2024-06-30 01:15:09.984027+00 | 2024-07-01 01:12:05.160881+00 pg_type | 2024-06-30 01:15:11.139648+00 | 2024-07-01 01:12:05.32726+00 ... (62 rows) David Rowley 於 2024年7月1日週一 下午6:52寫道： > On Mon, 1 Jul 2024 at 22:20, Pavel Stehule > wrote: > > The planners get min/max range from indexes. So some user's indexes can > be bloated too with similar effect > > I considered that, but it doesn't apply to this query as there are no > range quals. > > David >
Re: a lot of shared buffers hit when planning for a simple query with primary access path
On 1/7/2024 17:58, James Pang wrote: we have a daily job to do vacuumdb including catalog tables, and in same database , I did similar query with where=pk on another table and shared buffer access is very small, if catalog table bloat, should see similar shared buffer access when planning for other tables ,right? How to get more details about this planning ? relname | last_vacuum | last_analyze -+---+--- pg_statistic | 2024-06-30 01:13:08.703291+00 | pg_attribute | 2024-06-30 01:14:48.061235+00 | 2024-07-01 01:11:49.377759+00 pg_class | 2024-06-30 01:15:09.984027+00 | 2024-07-01 01:12:05.160881+00 pg_type | 2024-06-30 01:15:11.139648+00 | 2024-07-01 01:12:05.32726+00 ... (62 rows) David Rowley mailto:[email protected]>> 於 2024年7月1日週一 下午6:52寫道： On Mon, 1 Jul 2024 at 22:20, Pavel Stehule mailto:[email protected]>> wrote: > The planners get min/max range from indexes. So some user's indexes can be bloated too with similar effect I considered that, but it doesn't apply to this query as there are no range quals. David Don't forget about extended statistics as well - it also could be used. -- regards, Andrei Lepikhov
