optimizer_mismatch and hash_match_failed

I faced something today which I still haven't figured out. On couple of SQL we get a lot of child cursors (cursor_sharing=similiar) and for those of them that has HASH_MATCH_FAILED=Y in v$sql_shared_cursor I understand it is due to that setting.

but for one sql we get optimizer_mismatch=y (and 10% of them also hash_match_failed). I have checked them on v$sql_optimizer_env but no values there differs between the child cursors.

As reason in v$sql_shared_cursor we get :

<ChildNode><ChildNumber>0</ChildNumber><ID>3</ID><reason>Optimizer mismatch(12)</reason><size>2x212</size><_smm_max_size> 688120 KB 678290 KB </_smm_max_size><_smm_px_max_size> 3440640 KB 3391488 KB
</_smm_px_max_size></ChildNode><ChildNode><ChildNumber>0</ChildNumber><ID>3</ID><reason>Optimizer
mismatch(12)</reason><size>2x212</size><_smm_max_size> 701230 KB 691400 KB </_smm_max_size><_smm_px_max_size> 3506176 KB 3457024 KB
</_smm_px_max_size></ChildNode><ChildNode><ChildNumber>0</ChildNumber><ID>3</ID><reason>Optimizer
mismatch(12)</reason><size>2x212</size><_smm_max_size> 648800 KB

678290 KB           </_smm_max_size><_smm_px_max_size> 3244032 KB
3391488 KB          </_smm_px_max_size></ChildNode>

and these numbers on _smm_px_max_size and the others reported varies between the child cursors. But I don't know what is causing these values... The sessions comes from an application server with a shared pool of connections and is using jdbc against the db.

Where should I be looking further to find more information about these values? Could there be something that the application server forces? Could need some advice here :)

Thanks in advance
/johan

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