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rdbms 11.2.0.4

参考文档：

Active Session History (ASH) Performed An Emergency Flush Messages In The Alert Log (Doc ID 1385872.1)

alert log中信息

 解决方法：

CAUSE

Typically some activity on system causes more active sessions.  Therefore filling the ASH buffers faster than usual causing this message to be displayed. It is not a problem per se, just indicates the buffers might need to be increased to support peak activity on the database.

SOLUTION

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

select total_size from v$ash_info;

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. 

sqlplus / as sysdba
alter system set "_ash_size"=25165824;

You can verify the change using the following select:

select total_size from v$ash_info;

NOTE: The max setting for "_ash_size" is 254Mb, i.e. 127 chunks of 2 Mb chunksize (however, for 12c _ash_size can be set to a value greater than 254Mb).

You can submit a higher value but internally it is adjusted to 254Mb. Once 254 has been reached, and you try to set higher size, error
ORA-2097 will be dumped:

1. alter system set "_ash_size"=100m; verified it was set to 100 MB
2. alter system set "_ash_size"=300m; verified it was set to 250 MB
3. alter system set "_ash_size"=400m;
ORA-2097: parameter cannot be modified because specified value is invalid

END

本文标签： ASHperformedhistoryActivesession

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