Bad performance with 11.2.04 and nothing change when changing optimizer_features_enable

Hello,

I'm working on a software which has been developed many years ago.

The database model cannot really be change, some piece of the legacy code neither.

One of the action in the software generates a list of thousands of select with some insert in the middle (~30,000).

With an Oracle Server version 11.2.0.2 and 12.1.0.2, this group of queries take less than 30 seconds.

With an Oracle Server version 11.2.0.4 , it takes 5 minutes !

I have enable the tracing and run the TKPROF with it.

The explain plans on both version (11.2.0.2 and 11.2.0.4) aren't the same.

I've tried to change the optimizer_features_enable parameter to set it to the 11.2.0.2 but it didn't change anything.