CA XCOM z/OS VSAM History File Space Recommendation

Document ID : KB000122745
Last Modified Date : 10/12/2018
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I am not certain about the right measurement to determine utilization for the VSAM History file. I can't find documentation on how to determine the right sizes for everything VSAM related for the history file. 
You will need to estimate the maximum number of history records you will have at any one time. It is recommended to maintain your history file at regular intervals to backup and remove older records.
It is very important to use the DEFAULTS we ship for the history files, particularly for the DATA component's CISIZE and parameters for the AIX datasets, except for the number of CYLINDERS, of course.  The member CAI.CBXGJCL(DEFHIST) contains sample JCL to build the CA XCOM Data Transport History File and its associated indices and paths.  We make recommendations to use CISIZE 8192 to obtain a 1:1 ratio of records to CIs in VSAM for random access performance reasons. 

We do not recommend how to size your history file, but you can allocate your history file by specifying the number of RECORDS instead of CYLINDERS with the primary being the maximum number of history records you anticipate having and the secondary being the overflow protection. Then VSAM will do the calculation for you and add any additional bytes needed. 

IMPORTANT NOTE: Increasing the CISIZE above our recommended CISZ(8192)) will cause a lot of wasted space and I/O.
Additional Information:

Sample XCOMUTIL History File Purge Job (Member XCOMUTIL)

The member CAI.CBXGJCL(XCOMUTIL) contains sample JCL to maintain your history file at regular intervals.

If you want an explanation of how VSAM is managing the actual DASD space, you will need to consult IBM VSAM support. XCOM has no influence over how much space VSAM uses to store data on varying DASD devices. IDCAMS is the utility used to reload the VSAM XCOMHIST dataset from the flat file archive processed by the XCOMUTIL program.