Advanced Topics › Tuning Control File Access Rates › Control File Tuning: Analysis › Analysis Phase Summary

Analysis Phase Summary

By examining the DISPLAY IO statistics for every system in the MIMplex, you can identify certain systems that are not performing control file cycles often enough to keep pace with your workload-intense systems.

Disproportionate cycle rates (access frequencies), cause CA MIM on workload-intense systems to constantly reread and rewrite transactions that are destined for systems that are not accessing the control file often enough. The process of continuously rereading and rewriting latent transactions causes:

• More control file blocks to be used
• More control file I/O operations
• Elongated control file cycle times
• Inefficient transaction processing rates
• Less than optimum throughput

Based on the data in the DISPLAY IO illustrations that are used earlier in this section, the following analysis can be made: the MIMplex is communicating across systems using a DASD control file. The MIMplex is performing control file cycles at a rate of roughly 22 times per second. Control file cycles are most likely driven by the fact that it has a fairly high workload (the number of requests is 16,896,706). This MIMplex appears to be poorly tuned because of the following facts:

• The number of blocks that are read and written are more than the acceptable value of 1.1 for COMMUNICATION=DASDONLY.
• The average control file cycle time is longer than the acceptable value of 80 ms (for 3390 DASD control file).
• The transactions read to transactions processed ratio is more than the acceptable 10:1.

In short, there seems to be one or more external systems in the MIMplex that are not accessing the control file often enough, and this system is constantly having to reread and rewrite the transactions of that system. To determine which system is not accessing the control file often enough examine the DISPLAY IO data from the external systems.

Note: For help on correctly tuning a control file, see Control File Tuning: Example.

The purpose of the analysis phase is to help you identify which systems may not be accessing the control file often enough in your MIMplex. It can also be used to identify which systems may be dominating the control file due to enormous workloads, although this is rare. In any case, CA MIM parameters can be defined to increase or decrease control file cycles if the analysis phase shows CA MIM on certain systems to be accessing the control file too often, or not enough. The control file tuning sections on parameters and implementation in this chapter explain how to use these CA MIM parameters to increase or decrease control file cycles on specific systems.