Abend probabilities and workload management

CICSPlex® SM can evaluate the health and the activity (or load) of each region identified by the target scope. CICSPlex SM uses this information with the acceptable abend load threshold value (ABENDTHRESH) and the acceptable level of abend probability value (ABENDCRIT) that you provide when defining transaction groups to CICSPlex SM, in determining to which target region a transaction is routed.

In CICSPlex SM, the abend probability for transactions that are associated with a transaction group is calculated either for each transaction individually or for the entire group.
  • If the transaction is associated with a transaction group that either has no defined affinity relation and lifetime, or uses the default values defined in a workload specification, the abend probability is calculated individually for that transaction.
  • If the transaction is associated with a transaction group that has a defined affinity relation and lifetime, the abend probability for that transaction is calculated for the entire group of transactions.

The abend probability for transactions that are not associated with a transaction group is derived from the default abend probability values defined in the workload specification.

The acceptable abend load threshold value (ABENDTHRESH) and the acceptable level of abend probability value (ABENDCRIT) that you provide apply to both the health and the load of a potential target region. You can specify these values either in the workload specification (default rule) or a transaction group definition (associated with a specific rule) by using WUI or CICS®® TS Explorer, as shown in the following table:
Table 1. Fields for ABENDTHRESH and ABENDCRIT in WUI and CICS TS Explorer
Parameters WUI CICS Explorer
ABENDTHRESH Acceptable abend load threshold Threshold
ABENDCRIT Acceptable level of abend probability Critical
When an unhandled abend occurs in a target region:
  • For the transaction, or transactions associated with the transaction, that abends, the abend probability percentage is set to 100% in the target region, which is immediately considered unhealthy as a result.
  • CICSPlex SM then gradually reduces the abend probability percentage. When the abend probability percentage is below the specified acceptable level of abend probability (ABENDCRIT) yet above the specified acceptable abend load threshold (ABENDTHRESH), the target region is no longer considered unhealthy. However, the region's perceived load is doubled, making it proportionally less attractive as a target for routing than other equally loaded regions.
  • CICSPlex SM continues to reduce the abend probability percentage. When the abend probability percentage falls below the acceptable abend load threshold, the target region's load is set to normal, making it equally attractive as a target for routing as other equally loaded target regions.
  • If a further unhandled abend occurs at any point, the process is reset and the abend probability is recalculated from the initial starting point, where the region is considered unhealthy.
  • If the target region is considered unhealthy, CICSPlex SM attempts to avoid routing the transaction to that target region. However, if there is no healthier target region, the transaction might be routed to that target region.
Notes:
  1. Abend probabilities are taken into account only if you are using the dynamic routing exit DTRPGM. Abend probabilities are not considered if you are using the distributed routing exit DSRTPGM.
  2. If an affinity is active, all subsequent transactions are routed to the same target region for as long as the affinity remains active, regardless of its abend probability.
  3. If a transaction abends in a target region where the EXEC CICS HANDLE ABEND command is active, CICSPlex SM does not receive the information that the abend has occurred. Therefore, CICSPlex SM cannot take such abends into account when calculating the abend probability for the transaction in that target region. The abend probability might stay low in this situation, even though abends occurred.
  4. If an application avoids making calls to resource managers because it knows the connection to the resource manager is not active, or it processes an error return code as a result of the connection being unavailable, and proceeds to issue an error message and return normally rather than abend, it could delude the workload manager into routing more work to the CICS region. This situation is called the “storm drain effect”. See Avoiding the storm drain effect.