RE: Control File locks

This is from Oracle Metal Link.  

The CF locks are used to serialize controlfile transactions and read and writes on shared portions of the controlfile.

For example, these locks would be used for
- switching logfiles, held exclusive.

• updating checkpoint information for datafiles, held exclusive.
• opening a logfile for redo reading during recovery, held shared.
• getting information to perform archiving, held shared.
• performing crash recovery, held exclusive.
• adding a logfile or logfile member, held exclusive.
• dropping a logfile or logfile member, held exclusive.
• beginning a hot backup, held exclusive.
• ending a hot backup, held exclusive.

Hope it clarifies.  

Yuval.

-----Original Message-----
Sent: Tuesday, February 26, 2002 3:03 PM To: Multiple recipients of list ORACLE-L

Here is what Ixora has to say on Controlfile waits:

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

I'd still like to know is what can a user possibly do to modify a controlfile?

-----Original Message-----
Sent: Tuesday, February 26, 2002 2:34 PM To: Multiple recipients of list ORACLE-L

I noticed that my users are occasionally (once or twice a day) acquiring a 'CF' lock.
According to the oracle reference, 'CF' lock is a Control File lock. Does anyone know
why would users acquire a 'CF' lock, or in one case, even a 'IS' (Instance State) lock?
What situation can lead to that?

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Author: Yuval Arnon
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