Oracle RAC 10.2.0.3 increasing shared pool KQR L PO

Question

Hi,
I've got ORA-04031 on my 4 node 10.2.0.3 Linux RAC.
The top 3 shared pool occupants are:
SQL> r
  1  select * from (
  2  select * from v$sgastat where pool = 'shared pool' order by 3 desc)
  3  where
  4* rownum <= 3
POOL         NAME                            BYTES
shared pool  KQR L PO                    714319616
shared pool  sql area                    326563888
shared pool  free memory                 220592728Any idea what is KQR L PO responsible for ?
Regards.
Greg

Answer 1

Hi,
CauseThe shared pool is stressed and memory need to be freed for the new cursors. As a consequence, the dictionary cache is reduced in size by the LCK process causing a temporal hang of the instance since the LCK can't do other activity during that time. Since the dictionary cache is a memory area protected clusterwide in RAC, the LCK is responsible to free it in collaboration with the dictionary cache users (the sessions using cursors referenced in the dictionary cache). This process can be time consuming when the dictionary cache is big.
Solutiona. reduce the stress on the shared pool
=> by increasing it above the automatically reached value with dynamic sga, e.g.
when sga_target is set to 16G and the shared_pool_size was 6G during the hang time, set it to e.g. 8G.
=> by reducing the number of big cursors entering the shared pool, e.g. cursors using more than 1M sharable_mem e.g. via binding
select sql_text from v$sqlarea where sharable_mem > 1M;
b. reduce the dictionary cache usage in order to reduce the size of the dictionary cache, e.g.
=> when dc_histogram_defs is too high, it can point towards histograms calculations on all columns
of the tables. histograms should only be calculated on indexed columns
=> when dc_segments is high compared to dc_object_ids, it can point towards excessive partitioning usage. Reducing the partitions/subpartition usage will help reduce the dictionary cache usage to manage it.
c. set enableshared_pool_durations = false to avoid that one duration (a memory area in the shared pool used for a specific usage) need to give all space required for that usage, i.e. in case the duration containing the dictionary cache need to free memory, then that duration is extra stressed since no other type of memory from other durations can be used. Setting it to false make that any type of memory can be used to free space (i.e. any type of memory in the subpool). As a consequence, the number of subpools will be reduced by the factor of the number of durations (4 in 10gR2). Hence tuning the kghdsidxcount is advisable, e.g. increasing it to have manageable subpool sizes (see note:396940.1).
d. check patch:8666117 has been applied. This patch speedup the processing to free memory
Best regards,
Rafi.
http://rafioracledba.blogspot.com/