Active Session History (ASH) performed an emergency flush. This may mean that ASH is undersized.

 Error:-

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 8388608 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;

Solution:-

The current ASH size is displayed in the message in the alert log, or can be found using the following SQL statement.

SQL>  select total_size,awr_flush_emergency_count from v$ash_info;
TOTAL_SIZE AWR_FLUSH_EMERGENCY_COUNT
---------- -------------------------
   8388608                         1

Then increase the value for _ash_size by some value, like 50% more than what is currently allocated.  For example if total_size = 16MB, then an increase of 50% more would be (16MB + (16MB * 50%)) = 24MB.

SQL> alter system set "_ash_size"=12450000;

System altered.

SQL> select total_size,awr_flush_emergency_count from v$ash_info;

TOTAL_SIZE AWR_FLUSH_EMERGENCY_COUNT

---------- -------------------------

  12450000                         2