Advanced Topics › Performance Considerations › Tuning Control File Access Rates

Tuning Control File Access Rates

Control file cycles are driven by either of the following two events:

• Managed workload activity
• Timer expiration

Systems having higher managed workloads cause CA MIM Driver to access the control file more frequently than systems with little managed workload. By default, CA MIM accesses its control file one time per second. It is therefore possible to have CA MIM on some systems accessing the control file 20 or 30 times per second, while CA MIM on other systems is accessing the control file only one time per second. Environments generating such disproportionate control file access rates will not achieve the best possible transaction processing times.

The objective of control file access tuning is to provide a global (MIMplex-wide) balance of control file access rates; this ensures efficient transaction processing and, in turn, optimizes throughput on all systems in the MIMplex.

Tuning control file access rates is most critical for sites using the CA MII component of CA MIM. CA MII transaction processing has the lowest delay tolerance of any of the CA MIM component transactions. In other words, a delay in CA MII transaction processing has a more direct impact on system throughput than CA MIA or CA MIC transactions. If a CA MIA (tape device status) or CA MIC (message or command) takes one second to process, then it has little bearing on system throughout. However, if every CA MII enqueue transaction took 1 second to process, then this would severely degrade a workload-intense production system. Tuning control file access, while important for all CA MIM address spaces, is most critical for customers running the CA MII component of CA MIM. Therefore, this section is geared toward tuning CA MIM address spaces having the CA MII component activated. You can use the DISPLAY FACILITIES command to determine which CA MIM components and facilities are active in a given CA MIM address space.

Tuning control file access rates is important regardless of the control file architecture or medium being used in your particular environment. Balancing control file access rates is desirable regardless of whether you are using a DASD control file, an XES control file, or any of the virtual control file methods. The control file tuning methods outlined here are viable for all CA MIM control file architectures.

Tuning control file access rates is an exercise that should be undertaken several times per year or when changes are made to your MIMplex. Changes to, or shifting of, managed workloads can alter control file access rates such that a previously balanced MIMplex becomes disproportionate once again. It is also recommended that you examine control file performance after processor upgrades are performed, or when systems are added or removed from your MIMplex.

The process of tuning control file access rates involves two steps or phases. The Analysis phase involves issuing the CA MIM DISPLAY IO and DISPLAY SERVICE commands on all systems in the MIMplex, and then analyzing the data for indications of unbalanced control file access rates. The Implementation phase involves the manual manipulation of the CA MIM tuning parameters to increase or decrease control file access rates on one or more systems. The CA MIM parameters used during the implementation phase are SETOPTION MODE, INTERVAL, and CYCLE. The following sections on control file tuning explain the processes involved in tuning control file cycle rates.