Active Session History (ASH) Performed an Emergency Flush

We see alert log with below information :

“Active Session History (ASH) performed an emergency flush. This may mean that ASH is undersized. If emergency flushes are a recurring issue, you may consider increasing ASH size by setting the value of _ASH_SIZE to a sufficiently large value. Currently, ASH size is 134217728 bytes. Both ASH size and the total number of emergency flushes since instance startup can be monitored by running the following query:  select total_size,awr_flush_emergency_count from v$ash_info; ”

We can see current ASH size :

SQL> select total_size from v$ash_info;

TOTAL_SIZE
----------
 134217728

Current size is 134M according to query and messages in alert.log. We can add another 50% by sql below. The size should be fine without more similar message occurs. Otherwise increase it up to maximum 254M.

SQL>alter system set "_ash_size"=200M;

 

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