One of the issues that Database DBA face is oracle database memory set correctly or do I need to increase it.
Oracle 11g has cool solution.
Querying from table: v$memory_target_advice , tells if increasing memory size would provide any advantage, if so how much should you increase.
Here is the example:
Review the results in the screen shot. Currently database has a memory_target of 2048 MB (First line shows this).It can be compared with DB initialization parameter MEMORY_TARGET.
Line 2 shows that increasing memory size to 2560 MB (which is 25% more) did not add further benefit which can be seen in the column : EST_DB_TIME_FACTOR value 1. However, in line 3 if Memory size is 3072 (i.e. 50% more ) estimated time factor is 0.9602 that means 1 sec process can be done in 0.9602 sec this is an improvement.
Even if you increase memory by 75%, there is no additional benefit, but there is very minor benefit when memory is double.
In this scenario increasing memory by 50% is adding benefit for the database.
Oracle Enablement 