The DB2 database manager maintains data about its operation, its performance, and the applications using it. This data is maintained as the database manager runs, and can provide important performance and troubleshooting information. For example, you can find out:
Because collecting some of this data introduces overhead on the operation of DB2, monitor switches are available to control which information is collected. To set monitor switches explicitly, use the UPDATE MONITOR SWITCHES command or the sqlmon() API. (You must have SYSADM, SYSCTRL, or SYSMAINT authority.)
There are two ways to access the data maintained by the database manager:
Use the GET SNAPSHOT command from the command line; the Control Center on the OS/2, Windows 95, or Windows NT operating systems for a graphical interface; or write your own application, using the sqlmonss() API call.
The Control Center, available from the DB2 folder or with the db2cc command, provides a performance monitor tool that samples monitor data at regular intervals by taking snapshots. This graphical interface provides either graphs or textual views of the snapshot data, in both detail and summary form. You can also define performance variables using data elements returned by the database monitor.
The Control Center's Snapshot Monitor tool also allows you to define exception conditions by specifying threshold values on performance variables. When a threshold value is reached, you can predefine any of the following actions to occur: notification through a window or audible alarm, and/or execution of a script or program.
If you are taking a snapshot from the Control Center, you cannot perform an action that either alters, changes, or deletes a database object (such as an instance or database) while you are performing snapshot monitoring on either that object, or on any it its child objects. (In addition, if you are monitoring a partitioned database system, you cannot refresh the view of partitioned database objects.) For example, you cannot monitor database A if you want to remove its instance. If, however, you are monitoring the instance only, you can alter database A.
To stop all monitoring for an instance (including any of its child objects), select Stop all monitoring from the pop-up menu for the instance. You should always stop monitoring from the instance, as this ensures that all locks that are held by the performance monitor are released.
An event monitor captures system monitor information after particular events have occurred, such as the end of a transaction, the end of a statement, or the detection of a deadlock. This information can be written to files or to a named pipe.
To use an event monitor:
SET EVENT MONITOR evname STATE 1
If writing to a named pipe, start the application reading from the named pipe before activating the event monitor. You can either write your own application to do this, or use db2evmon. Once the event monitor is active and starts writing events to the pipe, db2evmon will read them as they are being generated and write them to standard output.
| Note: | If the database system that you are monitoring is not running on the same machine as the Control Center, you must copy the event monitor file to the same machine as the Control Center before you can view the trace. An alternative method is to place the file in a shared file system accessible to both machines. |
For information on the system database monitor and the event monitor, see the System Monitor Guide and Reference. For a scenario of how to use them from the Control Center, see the Administration Getting Started.