title: Check Undo Retention of Oracle Instances
agents: linux, aix, hp/ux, Solaris
catalog: app/oracle
license: GPL
distribution: check_mk
description:
 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 Check_MK {mk_oracle}-plugin installed in
 the agent. Please refer to the online documentation
 for how to install that plugin.

item:
 The SID of the database in uppercase (as appearing in the process
 name of the pmon_... process).

