Oracle Internals Notes

Wait event: refresh controlfile command

The refresh controlfile command wait event is not important for tuning, but can be helpful in problem diagnosis. It occurs when mounting a database, and when a controlfile transaction changes the range of used record numbers in any controlfile record section. This information is cached in the SGA and must be updated in all instances whenever it is changed by a controlfile transaction. Accordingly, a refresh controlfile command is sent to the CKPT process in each instance causing it to refresh the cached controlfile information in the SGA from the physical controlfile. While this is being done, the requesting process waits on the refresh controlfile command wait event.

The inter-process communication message that is used can be seen in X$MESSAGES as follows.

SQL> select dest, description from x$messages where description like 'refresh %';

DEST DESCRIPTION
---- ----------------------------------------
CKPT refresh control file