Data Files

The data store distinguishes VSAM data-file (DD) types by their names: structured DDs are called EQQSDFnn; unstructured DDs are called EQQUDFnn.

Although the datafile structure for these two types is the same, their content and purpose differ, as described below.

Unstructured data files

The Unstructured data files contain the SYSOUTs in a flat form, as provided by the JES spool. You can check the SYSOUT with the BROWSE JOBLOG function. Note that the unstructured data file can store, if requested, also the user SYSOUTs. The activation of the unstructured data files is optional, depending on appropriate data store parameters.

Within an unstructured data file, every SYSOUT, consisting of n logical records, takes at least one page of data (4096 bytes). The size of the VSAM data file depends on the following factors:

• The typical size of the SYSOUT for jobs that have to be stored (consider also the MAXSTOL parameter that specifies the number of user SYSOUT lines to be stored)
• The average number of jobs that run every day
• The retention period of job logs in data store
• The number of data files that you want to create (from 1 to 99)

You can calculate the number of pages that you need in this way:

• Calculate the maximum number of job logs that can be stored at a given time. To do this, multiply the number of jobs running in a day by the number of days that you want the job logs to be available.
• Calculate the average number of pages that are needed for every job log. This depends on the average number of lines in every SYSOUT and on the average SYSOUT-line length. At least one page is needed for every job log.
• Calculate the total number of pages required. To do this, multiply the number of job logs stored concurrently by the average number of pages for every SYSOUT.
• Calculate the number of pages required for each file. To do this divide the previous result by the number of Data Files you want to create.
• Determine size of each data file according to the media type and space unit for your installation.

Example of calculating for unstructured data files

A company runs 1000 jobs every day on a single system, and each job generates around 4000 lines of SYSOUT data. Most lines are 80 characters long. Restart and cleanup actions are taken almost immediately if a job fails, and so it is not necessary to keep records in the data store for more than 1 day.

A decision is made to spread the data over 10 files. The maximum number of logs stored at a given time 1 is: 1000 * 1 = 1000. As each log is about 4000 lines long, and each line is about 80 characters long, the number of bytes of space required for each is: 4000 * 80 = 320,000 Thus, the total number of bytes of space required is: 320,000 * 1000 = 320,000,000

If 4 files were used, each file would hold the following number of bytes of data: 320,000,000 / 4 = 80,000,000.

If 3390 DASD was used, each file would require this number of tracks: 80,000,000 / 56664 = 1412 or this number of cylinders: 80,000,000 / 849960 = 94

Structured data files

The structured data files contain job log SYSOUTs in a form based on the parsing of the three components of the job log, the JESJCL, the JESYSMSG and the JESMSGLG, especially the first two. User SYSOUTS are excluded from the structuring mode. Each job log stored consists of two distinct parts:

• A number of pages, each consisting of 4096 bytes dedicated to the expanded JCL
• A number of pages dedicated to a complete, hierarchically ordered set of structured elements for the restart and cleanup functions.

Therefore, the minimum page number used by a structured SYSOUT is 2, and the medium space usage depends on the job complexity.

To determine the optimal dimension for the structured data files, follow the instructions provided for the allocation of the unstructured data file, but take into account that the user SYSOUTs are not present. For the medium structured SYSOUTs, apply the criteria used for the unstructured job log: the larger memory requirement of the small, structured SYSOUTs, compared to the corresponding unstructured form, is balanced by the larger memory requirement of the unstructured form when the SYSOUT complexity increases.