Load Subsystem

The ACTIVE XACT, IMPEDE XACT, and THROTTLE WT fields on the Load screen help identify the source of transaction delays. In the following screen, these fields indicate two problems.

The first problem is that the transaction limit has been reached.

The transaction limit (MAX XACT) for the DBEnvironment is 5.0. The average number of active transactions (ACTIVE XACT) is also 5.0. When the transaction limit is reached, other sessions that attempt to begin a transaction are placed in the throttle wait queue. These sessions must wait until a transaction slot becomes free. Notice that on average one session is waiting in the throttle wait queue. You can increase the transaction limit by using

The second problem is that other sessions hold incompatible locks.

The current value of IMPEDE XACT is 1, which means that one active transaction is waiting to acquire a lock. On average, IMPEDE XACT is 3 and ACTIVE XACT is 5, which means that 3 out of 5 transactions are waiting.

This DBEnvironment definitely has a locking problem. At this point, you should use the Lock subsystem to obtain more information.

In a DBEnvironment with high throughput, transactions are completed quickly and successfully. The following screen shows that on average, 2 transactions are started and completed every 10.0 seconds.

On average, ROLLBK WORK is 0, which means that typically no transactions are rolled back. However, during the last refresh cycle of the LOAD screen, five transactions were rolled back.

To find out which sessions are rolling back transactions, access the Load Session screen. On the following screen, PID 26556 is responsible for most of the rolled back transactions.

You can see from the screen that the SET SORTLOAD 3 command has sorted the sessions in descending order according to ROLLBK WORK activity.

The Load screen also provides an overall view of the amount of lock contention in the DBEnvironment. In the example that follows, 25% of the lock requests are forced to wait. For detailed information on locking, you should use the screens in the Lock subsystem.