Merely summing them will give a falsely high value. Why is this done? Remember, this is sample data, so wait times are accumulating with each sample. Notice how the count of the samples is used to determine the time waited, not the WAIT_TIME or TIME_WAITED columns. Log file switch (private strand flush incomplete) 8 WHERE a.sample_time > SYSDATE - 5/(24*60) - 5 mins For example, if I wanted to see the main activity on the database for the last 5 minutes, I could use the following query. This makes it an incredibly flexible way of identifying what active sessions are doing, or have done. The V$ACTIVE_SESSION_HISTORY view is essentially a fact table, which can be linked to a number of dimensions to provide statistics specific to a variety of things including SQL statements, execution plans, objects, wait events, sessions, modules, actions, client identifiers, services and consumer groups etc. The sample information is written to a circular buffer in the SGA, so the greater the database activity, the less time the information will remain available for. An active session is one that is waiting on CPU or any event that does not belong to the "Idle" wait class at the time of the sample. Samples of wait event information are taken once per second and made available using the V$ACTIVE_SESSION_HISTORY view. It samples information from the V$ views allowing you to see current and historical information about active sessions on the database.īeing part of the Diagnostics and Tuning Pack means ASH is only available as a paid option on top of Oracle Database Enterprise Edition. Oracle 10g introduced the Active Session History (ASH) as part of the Diagnostics and Tuning Pack. The V$ dynamic performance views provide masses of real-time information, but it can be difficult for beginners and experienced people alike to make good use of this information. Tools like Statspack, AWR, ADDM and SQL Trace are all very useful for gathering wait event information during tuning, but they tend to focus on looking back at what has happened, rather than what is currently happening. Active Session History (ASH) Analytics in Oracle Enterprise Manager Cloud Control 12cįor a long time DBAs have been encouraged to use variations on the YAPP method of performance tuning, which focuses on wait event monitoring, rather than hit ratios.Automatic Database Diagnostic Monitor (ADDM) in Oracle Database 10g.AWR Baseline Enhancements in Oracle Database 11g Release 1.Automatic Workload Repository (AWR) in Oracle Database 10g.Home » Articles » 10g » Here Active Session History (ASH)
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