Re: buffer cache -once again

Hi,

    It is an important parameter, if you system is an OLTP one, do not change it.It maybe will change the CBO, and make it make FTS more possible, thus make more SQL doing full table scan.     If you know most of your SQL should do FTS, then enlarge it will do some good, I think. Regards
zhu chao
msn:chao_ping_at_163.com
www.cnoug.org(China Oracle User Group)
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Thursday, May 08, 2003 5:51 PM

> zhu chao,
>
> is there any problem if i increase the value of
> db_file_multiblock_read_count to its
> maximum value 128 , or its require special attention to be given at some
> other part also.
>
> -----Original Message-----
> Sent: Thursday, May 08, 2003 2:07 PM
> To: Multiple recipients of list ORACLE-L
>
>
> Hi,
> With db file scattered read, if it is not a datawarehouse db, you must
> tune your SQL. It means there is a lot of full table scan/full index scan.
> If the full table scan is necessary, then increasing
> db_file_multiblock_read_count is good. Though it is still the no.1 wait
> event, pay attention to the ratio of this event waited.If the ratio
> decreased, it means you are doing good.right?
> Tune some os parameter like stripe size, maxphys(in solaris, not knowing
> the corresponding parameter in aix) will also help.
>
> Regards
> zhu chao
> msn:chao_ping_at_163.com
> www.cnoug.org(China Oracle User Group)
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> Sent: Thursday, May 08, 2003 2:36 PM
>
>
> > Dennis,
> >
> > earlier my buffer cache was 300MB that time the cache hit ratio was
> 81%
> > ,so i thought to increase the size by 100mb and incresed .but again the
> > cache hit ratio is 81%.means the problem
> > is not the buffer cache.
> >
> > the top wait event is 'db file scattered read' ,i increased the
> > db_file_multiblock_read_count from 16 to 64 but still this the top one
> wait
> > event.
> >
> > db version is 8.0.5 ,OS is AIX 4.3 on RS/6000.
> >
> >
> > pls suggest if need to correct something ...
> >
> > Thanks
> >
> >
> > Arvind
> >
> >
> >
> > -----Original Message-----
> > Sent: Tuesday, May 06, 2003 7:42 PM
> > To: Multiple recipients of list ORACLE-L
> >
> >
> > Arvind
> > What makes you suspect you've configured your buffer cache too large? A
> > better question might be "how can I tell if my buffer cache is properly
> > sized?". Start by checking your wait times. What are your top 3 waits?
> Also,
> > what is your (cough, cough) average buffer hit ratio?
> >
> > Dennis Williams
> > DBA, 60%OCP, 100% DBA
> > Lifetouch, Inc.
> > dwilliams_at_lifetouch.com
> >
> >
> > -----Original Message-----
> > Sent: Tuesday, May 06, 2003 4:37 AM
> > To: Multiple recipients of list ORACLE-L
> >
> >
> > Dear All,
> >
> > how can i check if my buffer cache is bigger than necessary ?oracle db
> > version is 8.1.7.
> >
> >
> > Thanks
> >
> >
> > Arvind
> >
> >
> > --
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > --
> > Author: Arvind Kumar
> > INET: arvindk_at_sqlstarintl.com
> >
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> --
> Author: zhu chao
> INET: chao_ping_at_vip.163.com
>
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> Author: Arvind Kumar
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: zhu chao
  INET: chao_ping_at_vip.163.com

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