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The DISPLAY IO command provides information about your control file-processing environment.
Important! Every CA MIM address space has unique control file processing data.
Therefore, issue the DISPLAY IO command on every system in the MIMplex, and examine it on a system-by-system basis. Among the information, provided is:
A great deal of information is displayed, however, the most important statistics involve the control file cycle rates and transaction processing data. The following illustration shows the DISPLAY IO data:
MIM0039 CONTROL FILE I/O DISPLAY: COMMUNICATION=DASDONLY CURRENT=DASD MODE=DEMAND CYCLES=1 INTERVAL=1.000 FILE=00 NAME=MIM.PRIMARY UNIT=2DC8 TOTAL BLOCKS=1200 MAX USED=547 FREE=1199 BLKSIZE=6144 LAST FORMAT: 2003.119 TOTAL READS=408.463M WRITES=220.841M LAST RESTART AT 07:59:53 ON 2003.119 COUNT: CYC=15.166M BLOCKS READ=57.638M8 WRITTEN=27.639M XACT READ=88.885M PROCESSED=44.093M WRITTEN=26.650M AVG: CYC=0.085302 BLOCKS READ=3.788 WRITTEN=4.120 XACT READ=95.529 PROCESSED=2.907.000 WRITTEN=1.757 RATE: CYC=21.571 BLOCKS READ=165.584 WRITTEN=79.404 XACT READ=2400.309 PROCESSED=120.025 WRITTEN=76.561
The key fields used in the control file tuning analysis phase have been bolded in the preceding illustration. The following describes each of these key fields:
Represents the average control file cycle completion time in seconds. It is comprised of:
For example, the control file cycles on this system are taking 85 milliseconds, which is not acceptable for a 3390 DASD control file.
Note: The faster the control file cycle time, the more optimized CA MIM performance.
Indicates, on average, how many control file blocks are read from and written to the control file during each control file cycle. Optimally tuned MIMplexes have a value of less than 1.1 for each of these fields when COMMUNICATION=DASDONLY is specified.
A higher value usually means one or more CA MIM address spaces are not accessing the control file frequently enough. The transactions destined for those systems are constantly read and rewritten by CA MIM on your more active, workload intense systems. Values of 3.788 and 4.120 as shown in the example are not considered acceptable.
If COMMUNICATION=CTCDASD/CTCONLY/XCF is specified, then it may be acceptable to have BLDS READ and BLKS WRITTEN larger than 1.1. When CA MIM uses a virtual control file, the data is read and written using VCF buffers. The MIMINIT VCFBUFFERSIZE statement, with a default of 32768, determines the size of this buffer. The maximum number of blocks of data are "packed" into this VCF buffer, when it reads and writes data to the VCF master system. Current BLKSIZE value determines the amount of data in each block. Use the DISPLAY IO command to displays this value.
Examples:
AVG BLOCKS READ value is 2.0 and MIMINIT BLKSIZE is 6144, then CA MIM usually reads 12288 bytes of data during each control file transaction.
AVG BLOCKS READ value is 7.0 and MIMINIT BLKSIZE is 6144, then CA MIM usually reads 43008 bytes of data during each control file transaction.
VCFBUFFERSIZE value is 32768. CA MIM is not able to fit all of the data into one VCF buffer, and requires multiple VCF buffers for each control file access. The number of I/Os required are increased to complete each control file cycle. A more appropriate value for VCFBUFFERSIZE in this example would be 44000.
This field represents the number of control file cycles per second. The frequency of control file cycles is driven by either of two events:
CA MIM on a system with large amounts of managed enqueue requests, accesses the control file more frequently.
Each CA MIM address space on a MIMplex containing systems running heavy to light enqueue workloads ranges, access the control file at different frequencies..
CA MIM on a production system performs control file cycles at a rate of 25 times per second. On a test system, CA MIM performs a control file cycle only one time per second. Severely disproportionate control file access rates by CA MIM on different systems elongate individual control file cycle times, and degrade CA MIM transaction processing times. Acceptable values for this field vary from site to site depending upon a number of factors. If this value is too high, then CA MIM address space CPU consumption increases. If this value is too low, then MIMplex throughput suffers.
For most sites, this value is set to 30 or less on any system. Some sites, however, use XES control files with average cycle rates as high as 45 control file cycles per second with great success. The number of control file cycles per second can be increased or decreased on a system-by-system basis. For more information see, Control File Tuning: Implementation.
These fields represent the average number of transactions read, and the number of transactions processed by this system, during each control file cycle. In CA MIM, transactions remain in the control file for a very short time. Once a transaction is read and processed by all CA MIM address spaces, that transaction is removed from the control file.
During every control file cycle, the CA MIM address space reads in every transaction from the control file. CA MIM examines the routing mask to determine the transaction needs for processing by this system. A transaction previously processed by an earlier control file cycle is written back to the control file with new transactions. The process of reading constantly, but not process the transactions of other systems, causes the Transactions Read to Processed ratio to increase.
Ideally, you want every CA MIM address space to process at least one out of every ten transactions it reads from the control file. The preferred Transactions Read to Processed ratio is within 10 to 1. This ratio can be calculated by dividing the Transactions Read value by the Transactions Processed value. In the above example, during each control file cycle this system reads, on average, 2400 transactions from the control file. Where only 120 transactions are destined for this system. This means that during every control file this system is reading 2280 transactions that are not for this system. The Transactions Read to Processed ratio in the example is roughly 20 to 1, which is not acceptable. Increasing or decreasing the number of control file cycles per second on certain systems will correct this problem.
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