Diving Into the Shared Pool - An In Depth Look at Tuning the Shared Pool (Part 2) Oracle Tips by Mike Ault

A Matter Of Hashing
 

A quick glance at the report in Figure 5 shows that I need to look at the DCARS user to correct  hashing problems they might be having and improve the reuse of SQL in the shared pool. However, look at the number of hash areas this user has accumulated, 6,484, if I run the report from figure 7 in last months article it will out weigh the paper version of the Oracle documentation set. A faster way to find the hash values would be to do a self join and filter out the hash values that are duplicate. Sounds easy enough, but remember, the V$ tables have no rowids so you can’t use the classic methods, you have to find another column that will be different when the HASH_VALUE column in V$SQLAREA is the same. Look at the select in Figure 6.

select distinct a.hash_value from v$sqlarea a, v$sqlarea b, Remote DBA_users c

SEE CODE DEPOT FOR FULL SCRIPT

and c.username='DCARS' and  ß change to user you are concerned about

a.FIRST_LOAD_TIME != b.FIRST_LOAD_TIME

Figure 6: Example Select To Determine Duplicate Hash Values

Figure 7 has an example output from the above select.
 

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