AWR vs ADDM vs ASH :


AWR : automatic workload repository

The AWR is used to collect performance statistics including:

    Wait events used to identify performance problems.
    Time model statistics indicating the amount of DB time associated with a process from the V$SESS_TIME_MODEL and V$SYS_TIME_MODEL views.
    Active Session History (ASH) statistics from the V$ACTIVE_SESSION_HISTORY view.
    Some system and session statistics from the V$SYSSTAT and V$SESSTAT views.
    Object usage statistics.
    Resource intensive SQL statements.


 ADDM : automatic database diagnostic monitor


Analyzes data in the Automatic Workload Repository (AWR) to identify potential performance bottlenecks.and we use it for the following cases :

         CPU bottlenecks
         Undersized memory structures
         I/O capacity issues
         High load SQL statements
         RAC specific issues
         Database configuration issues
         Also provides recommendations on hardware changes, database configuration & schema changes.

Generate ADDM  :

    Login to SQL
    @$ORACLE_HOME/rdbms/admin/addmrpt.sql
     enter system password when you asked for .
    Specify a begin_snap from the list and press Enter.
    Specify the end_snap from the list and press Enter.
     Report Name

ASH : Active Session History

statistics from the in-memory performance monitoring tables also used to track session activity and simplify performance tuning.

ASH reports Give the following information :

    Top User Events (frequent wait events)
    Details to the wait events
    Top Queries
    Top Sessions
    Top Blocking Sessions
    Top DB Object.
    Activity Over Time

 Generate ASH reports :

The Best way to do that using OEM.  (Enterprise manager).