Why Oracle automatic memory management is often a bad idea

Oracle might had created this feature for those whom doesn´t have a DBA onsite and need a database that can operate by itself.

The use of AMM is not free of charge, many peak of usage in one area often lead to future decrease in performance in another area.

 

e.g. If a bad query loads tons of cache in database buffer, and Oracle deallocate memory from shared pool to accomplish this request, eventually the whole database will pay a huge price with decreasing in performance due to lack of information at shared pool.

 

So the botton line is, if your database have someone watching close to it,  don´t use AMM.