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

Control File Tuning: Parameters

In practice, any of the communication media perform adequately for CA MIA and CA MIC, using default values for all of the tuning parameters. However, balancing control file cycles across the MIMplex:

• May improve transaction processing efficiency
• Reduce control file block count usage
• Reduce the average control file cycle time
• Improve overall MIMplex throughput

This section provides you with 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 alter the CA MIM internal control file cycle processes dynamically. The result of these commands is to either increase or decrease control file cycles on a given system. The following parameters are used to tune CA MIM control file cycle rates.

SETOPTION MODE=DEMAND/GROUPS

When running in DEMAND mode, mostly local CA MIA resource activity drives local control file cycles. When CA MIA activity is not present, CA MIM Driver performs a control file cycle at the expiration of a timer value. This value is calculated based on your SETOPTION CYCLE and INTERVAL parameters. DEMAND is the default processing mode as it allows CA MIA 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 for local CA MIA or CA MIC transactions to propagate, and then performs a control file cycle. In this case, local transactions are any that have been queued or grouped while waiting for the timer to expire. 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 preferred mode of operation.

DEMAND MODE can be used to increase control file cycles on systems that do not have enough CA 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 because they have so much managed activity that they perform control file cycles at an excessive rate. This domination causes other systems to be locked out of the control file resulting in intermittent MIM0100 or MIM0200 messages. In these cases, we recommend 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 occurred when the INTERVAL parameter is set to a particular value in GROUPS mode with 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.