Oracle 10.2.0.4 high load triggering ORA-00494 Error

 

An article on MOS specifically introduces this issue. For details, refer to [ID 779552.1].

 

In Oracle 10.2.0.4, the following error may occur in Alert Log:

ORA-00494: enqueue [Cf] held for too long (more than 900 seconds)

 

This error usually occurs with the ORA-600 [2103. They have the same causes. The process cannot obtain the CF queue within the specified time (900 seconds by default.

 

Generally, the Oracle process occupies the relevant resources and is not released only when the system is in high load, high concurrency, Io waiting and competition.

 

Two bugs may cause this problem:

(1) bug7692631-'database crashes with ORA-494 after upgrade to 10.2.0.4'

(2) Unpublished bug 7914003 'Kill blocker after ORA-494 leads to fatalbg process being killed'

 

Solution:

All block processes, including background and non-background processes, are killed in the Oracle mechanism of 10.2.0.4. Note that:

(1) If the non-background process holder has CF enqueue, kill the process and the instance can run normally.

(2) if it is a background process, such as lgwr holder, kill lgwr will cause dB crash.

 

To avoid killing blocker processes (background and non-background processes), you can set the following parameters:

_ Kill_controlfile_enqueue_blocker = false.

 

In this way, no blocker process will be killed. Even if the process holds the enqueue for a long time. In general, it is best to avoid kill background processes and allow kill non-background processes.

 

To prevent background processes from being killed, you can set the parameter _ kill_enqueue_blocker = 1 in the init. ora file. The default value of this parameter is 3.

 

After this parameter is set, if the enqueue is holder by the background process, the background process will not kill. So the instance does not crash. If the enqueue is not a background process holder, the 10.2.0.4 mechanism will still try to kill non-background processes.

 

Oracle retains the ORA-494 because the user prefers instance crash, and DB will hang without crash.

 

 

 

 

 

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