Advanced Topics › Performance Considerations › Tuning Control File Access Rates › Control File Tuning: Parameters

Control File Tuning: Parameters

Balancing control file cycles across the MIMplex will improve transaction processing efficiency, reduce control file block count usage, reduce the average control file cycle time, reduce individual enqueue service time, and improve overall MIMplex throughput. The objective of this section is to provide an understanding of the CA MIM parameters that are used to regulate control file cycle rates on one or more systems in the MIMplex. The CA MIM SETOPTION commands can be used to dynamically alter the CA MIM internal control file cycle processes. The result of these commands is to either increase or decrease control file cycles on a given system. Let us take a look at the parameters used to tune CA MIM control file cycle rates.

SETOPTION MODE=DEMAND/GROUPS

When running in DEMAND mode, mostly local CA MIA or CA MII resource activity drives local control file cycles. If no CA MIA or CA MII activity is present, then CA MIM Driver performs a control file cycle at the expiration of a timer value, which is calculated based on your SETOPTION CYCLE and INTERVAL parameters. DEMAND is the default processing mode as it allows CA MII enqueue activity to be handled in the most expedient manner. When running in GROUPS mode, local control file cycles are not driven by local managed resource activity, but by a timer expiration. GROUPS mode processing waits for a timer to expire, then checks to see if there are local CA MIA or CA MII transactions to propagate (any that have been queued/grouped while waiting for the timer to expire), and then performs a control file cycle. Because DEMAND mode processing performs a control file cycle as soon as access to a locally managed resource is requested (on demand), it is the more preferred mode of operation.

DEMAND MODE can be used to increase control file cycles on systems that do not have enough CA MIA or CA MII activity to keep pace with other more heavily loaded systems. When running in DEMAND mode, CYCLE=1, and reducing the INTERVAL value from its default of 1, you can force control file cycles to occur more frequently. The following table illustrates the number of control file cycles that occur when you set the INTERVAL parameter to a particular value when in DEMAND mode.

Using this technique you can increase the number of control file cycles to an appropriate level. For example, if you found that CA MIM on a system was performing control file cycles only one time per second, you could issue a SETOPT MODE=DEMAND,CYCLE=1, INTERVAL=.1 command on that system and CA MIM on that system would immediately begin performing control file cycles at a rate of 10 times per second.

GROUPS MODE is typically used to decrease the number of control file cycles. On rare occasions, some systems dominate the control file due to the fact that they have so much managed enqueue activity that they perform control file cycles at an excessive rate. This causes other systems to be locked out of the control file resulting in intermittent MIM0100 or MIM0200 messages. In these cases, it may be recommended that you place CA MIM on that system in GROUPS mode, set CYCLE to 1, and use the INTERVAL value to reduce the control file access rate. The preceding table illustrates the number of control file cycles that will occur when you set the INTERVAL parameter to a particular value when in GROUPS mode and have CYCLE set to 1.

Using this technique, you can decrease the number of control file cycles to an appropriate level. For example, if you found that CA MIM on a system was performing control file cycles at an excessive rate of 60 times per second when in DEMAND MODE, you could issue a SETOPT MODE=GROUPS,CYCLE=1, INTERVAL=.04 command on that system and CA MIM would immediately begin performing control file cycles at a decreased rate of only 25 times per second.

While running CA MIM in GROUPS mode on a system will reduce the number of control file cycles and reduce CA MII address space CPU consumption, it will also degrade CA MII enqueue service times. Therefore, placing a CA MIM address space in GROUPS mode should be performed only after consulting with Technical Support.