Oracle Instance: Undo Retention
This check monitors the Undo Retention in the current Database Instance.
The Undo information is very important in Oracle for read consistency
of SQL statements. In older time, there was no real monitoring of Undo
information and most users did only a monitoring of the Undo Tablespace
where that data is placed. Oracle introduced with 9i a new parameter
called undo_retention. The value describes the amount in seconds of
data that should be hold in the undo Tablespace.
The v$undostat has a column 'tuned_retention' which displays the
current number of seconds of Undo data availibe for read consistency.
This value could be monitored with this check.
The other important counter is nonspaceerrorcnt which counts the number
of 'out of space' events in the Undo Tablespace due to big amount of needed
data from current active transactions.
Normaly the checks goes to CRITICAL when a space error occurs. After ~
10 minutes the counter is resetted back to 0 and the state is OK again.
The state for this event could be configured with nospaceerrcnt_state.
There is no real usable value for the minimum amount of space errors.
This check needs the Checkmk
mk_oracle-plugin installed in
the agent. Please refer to the online documentation
for how to install that plugin.
The SID of the database in uppercase (as appearing in the process
name of the pmon_... process).
One service is created for each running database.