Tuning the memory structure

Question

Hi folks,
I have lots of misses in library cache. Can someone tell me how I can identify or fix the problem?
SQL> SELECT Sum(pins) AS "Executions", Sum(reloads) AS "Cache Misses while Executing", Round(Sum(reloads) / Sum(pins) * 100, 2)
AS "Misses Ratio, %" FROM v$librarycache;
Executions Cache Misses while Executing Misses Ratio, %
1389008 17415 1.25
I used to run the above sql with the following result:
Executions Cache Misses while Executing Misses Ratio, %
26558 315 1.19
Thanks,
Amir

Answer 1

Hello Amir,
The stats that you have given in the thread are not so bad... that you need to worry. I would recommend you not to change much if your library cache hit ratio is around 99%. By adding more space to library cache you can increase the hit ratio and reduce the misses on library cache, but having too big library cache is also not recommended
To identify the problem I would problem that you use statspack report and find out the SQL that has low hit ratio. You might find out that application has a un-named block which is used repetitively or the similar type of SQL implemented in different ways e.g. not using bind variables
Using the statspack report you would be more equiped to reduce the misses or increase the hit ratio
I have personally learnt not to bother much about hit ratios or misses. They should be just okay, more important are blocking events, again statspack report is good one to show such database activities
Regards
Sudhanshu
Message was edited by:
Sudhanshu