Question: I am getting "MMON
suspending action" messages in my alert log and my instance
is not allowing new SQL*Plus sessions. A trace files
also shows ORA-12751 errors.
"DDE rules only execution for: ORA 12751 ". So, how so
I address this MMON suspending action errors and connect to
You can connect to your instance using the
-prelim option or by
killing your oracle
instance and re-starting the instance.
The MMON background process is responsible for the
collection of statistics for the Automatic Workload
Repository (AWR). As Oracle becomes over-stressed, he
shuts-down non-critical background processes such as MMON.
occurred while spawning process m000; error = 12751
MMON action 'Block Cleanout Optim, Undo Segment Scan' for
Suspending MMON action 'tablespace alert
monitor' for 82800 seconds
Suspending MMON action 'recovery area
alert action' for 82800 seconds
Suspending MMON action 'AWR Auto Flush
Task' for 82800 seconds
Suspending MMON action 'AWR Auto CPU
USAGE Task' for 82800 seconds
Suspending MMON slave action kewfmadsa_
for 82800 seconds
Suspending MMON action 'undo usage'
for 82800 seconds
action 'undo usage' for 82800 seconds
action 'metrics monitoring' for 82800 seconds
As we see, MMON will suspend actions where there is a
large enqueue of background tasks waiting for service, or
any case of server resource exhaustion. MMON is not
critical to Oracle operations, hence it is suspended as a
instance survival mechanism.
The solution is tuning SQL to use less computing
resources or adding either RAM or CPU to the server . . .
In this case the root cause appears to be CPU exhaustion,
a case of CPU exhaustion where the runqueue exceeds the
number of CPU's on the server. See my notes on
usage. The MMON process can
also be suspended for a shortage of RAM resources (see swap
RAM and total RAM usage) or a shortage of other server
resources. See my book
Oracle Tuning: The Definitive Reference 3rd edition" for
isolating the exact server resource problem
For more details see these
- MOSC note
1478691.1 titled "Minact-scn:
Useg Scan Erroring Out With Error E:12751".
- MOSC Note 761298.1 titled "MMON Suspended Due
to ORA-12751 "cpu time or run time policy violation".
- MOSC Note 1291296.1 titled "ORA-12751 "cpu
time or run time policy violation" in the MMON Slave
Process File during Feature Usage Statistics [FUS]".
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