Some hot objects related issue in x$bh

Question

Does this query can be used to keep the object in the keep buffer pool
My db version is oracle 9.2.0.6
set lines 80;
set lines 999;
column avg_touches format 999
column myname heading 'Name' format a30
column mytype heading 'Type' format a10
column buffers format 999,999
select object_type mytype,object_name myname,
blocks,count(1) buffers,avg(tch) avg_touches
from sys.x$bh a,
dba_objects b,
dba_segments s
where
a.obj=b.object_id
and
b.object_name=s.segment_name
and
b.owner='CD'
group by
object_name,object_type,blocks,obj
having avg(tch)>5
and count(1)>20;
/Edited by: user00726 on Feb 3, 2009 11:18 PM
Edited by: user00726 on Feb 3, 2009 11:22 PM

Answer 1

user00726 wrote:
Does this query can be used to keep the object in the keep buffer pool
from sys.x$bh a,
dba_objects b,
dba_segments s
where
a.obj=b.object_idNo - none of the scripts in this series of posting tells you anything useful regarding the KEEP pool. In particular, your script joins to the wrong column in dba_objects - it should use data_object_id.
The best way to check the benefits of setting up a keep pool are (for your version of Oracle) to run statspack at level 7 (the default is level 5) and check the segment statistics section of the reports to see if there are any objects which are responsible for a large amount of physical I/O that would give you a lot of benefit if you could "KEEP" them, without sacrificing a lot of memory that might cause other objects to start doing more physical I/O.
There is one particular benefit of the KEEP pool that can be of short term benefit (in your version of Oracle) - there is a bug with the touch count algorithm in 8i and 9i which means that blocks read for short tablescans do not get their touch count incremented: so if you are doing lots of short tablescans and see the relevant tables appearing high in the physical read report, then you could create a KEEP pool for them. However, you ought then to work out why they are being scanned so much when its possible they should be subject to indexed access.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
"Science is more than a body of knowledge; it is a way of thinking"
Carl Sagan
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