Abstract for JES2 Initialization and Tuning Guide · How to send your comments to IBM · Summary How to initialize JES2 in a multi-access SPOOL configuration. JES2 Initialization and Tuning Guide. z/OS JES2 Initialization and Tuning Guide contains the following information in support of JES2 Email Delivery Services. JES2 initialization statement and parameter summary tables · JES2 initialization statement descriptions · APPL(jxxxxxxx) – Application Characteristics.
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Spooling means a holding area on disk is used for input jobs waiting to run and output waiting to print.
The holding area is called spool space. The imagery of spooling was probably taken from processes that wind some material such as thread, string, fabric or gift wrapping paper onto a spindle or spool. In effect, spooling is a near-synonym for queueing. Those paper towels on that roll in the kitchen are queued up waiting for you to use each one in turn, just like a report waiting to be printed or a set of JCL statements waiting for its turn to run.
On very early mainframe computers, the system read input jobs from a punched card reader, one line at a time, one line from each punched card. It wrote printed output to a line printer, one line at a time.
Red books JES2 Performance and Availability Considerations
Compared to disks — even the slower disks used decades ago — the card readers and line printers were super slow. Bottlenecks, it might be said. The system paused its other processing and waited while the next card was read, or while the next line was printed.
So that methodology was pretty well doomed. It was okay as a first pass at getting a system to run — way better than an abacus — but that mega bottleneck had to go. See HASP origin storyif interested.
We will focus on JES2 in this article because it is more widely used. Besides initializatioj queueing the input and output, the spooling subsystem schedules it. The details of the scheduling form the main point of interest for most of us. Preliminary to that, we might want to know a little about the basic pieces involved.
Sample JES2 initialization data set
There are input classesalso called job classes, that control scheduling and resource limits. There are real physical devices few card readers, but many variations of printers and vaguely printer-like devices. There are virtual devices. An external writer is a program that reads and processes sysout files, and such a program can route the output to any available destination.
Many sysout files are never really printed, but are viewed and further processed directly from the spool space under TSO using a software product like SDSF. There is spool sharing. Each such system has a copy of JES2 running. Together they form a multi-access spool configuration MAS. This is obviously especially necessary when spool sharing is in use.
There are separate JES2 operator commands that the system operator can use to control the spooling subsystem, for example to change what classes of sysout can be sent to a specific printer, or what job classes are to be processed.
IBM z/OS V1R JES2 Initialization and Tuning Reference (SA) – United States
There is a set of very JCL-like control statements you can use to specify your requirements to the spooling subsystem. The meanings of the individual job classes are totally made up for each site.
Some small development company might have just one job class for everything. Big companies typically create complicated sets of job classes, each class defined with its own limits initializatioon resources such as execution time, region size, even the time of day when the jobs in each class are allowed to run.
Your site can define how many jobs of the same class are allowed to run concurrently, and the scheduling selection priority of each class relative to each other class. If you want to know what job CLASS to specify for your various work, your best bet is to ask your co-workers, the people who are responsible for setting up the job classes, or some other knowledgeable source at your company. In some cases similar considerations initializahion apply for the use of SYSOUT print classes and the routing of such output to go to particular printers or to be printed at particular times.
However, there is no way to know for sure the details of how classes are set up at your particular site unless you ask about it. Ask around about the local rules and expectations. Classes are set up by your site, for your site. The idea for this post came from a suggestion by Ian Watson. Skip to content Skip to main menu Resources Disclaimer. The Basic pieces There are input classesalso called job classes, that control scheduling and resource limits There are output classesalso called sysout classes, that control output print There are real physical devices few card readers, but many guie of printers and vaguely printer-like devices There are virtual devices.