SQL WITH MOST BUFFER SCAN NOTES:

Username - Name of the user

Buffer Gets - Total number of buffer gets for this statement

Executions - Total number of times this statment has been executed

Gets/Execs - Number of buffer gets per execution

SQL Text - Text of the SQL statement requiring the cursor, or the PL/SQL anonymous code

The buffer_gets column provides information on SQL statements that may not possess the large disk hits, but possess a large number of memory hits (higher than normally desired). In this case, the SQL statement may be using an index, but using the wrong index. These types of SQL statements can involve a join operation that is forcing the path to utilize a different index than desired or using multiple indexes and forcing index merging.

Excessive BUFFER_GETS suggests that the query is causing heavy memory (logical) reads

Check for overindexes tables