What’s In a Identify? Mainframe GDGs Get the Job Finished

Mainframes are completely different. They’re the most important, quickest, most succesful techniques on the planet, they usually nonetheless run many, if not most, of an important purposes within the business world.

One motive mainframes stay dominant? Their lengthy historical past of successfully coping with enterprise knowledge.

In large-scale enterprise knowledge processing environments, a standard requirement is the necessity to take care of many alternative successive units of the identical kind of information. Day by day recordsdata result in weekly recordsdata, which then roll up into month-to-month and yearly recordsdata, all of which should be simply accessible both individually or as a gaggle, within the desired order.

Because the early days of mainframes, the Technology Information Group (GDG) has been the technique of managing these successive occurrences (or ‘generations’) of the identical knowledge. Just by utilizing the dataset title, purposes can choose a present or prior technology, create new generations, or use the whole assortment of datasets (a ‘GDG-all’) request.

This highly effective but easy methodology of managing knowledge is exclusive to z/OS.

Tips on how to Create a Mainframe GDG

Earlier than the person datasets that comprise a GDG could be created, a GDG ‘base’ entry is created within the catalog by IDCAMS. As soon as the GDG base is created, particular person technology datasets (GDSs), that are usually unusual sequential datasets, could be created.

A DEFINE assertion, just like the one under, accomplishes just a few various things:

• Creates the GDG base entry
• Units the variety of generations to maintain monitor of
• Specifies what to do when the utmost variety of technology datasets is reached

DEFINE GDG(NAME(MY.BUSINESS.DATA)) LIMIT(255) NOEMPTY SCRATCH

Within the instance above, every particular person technology knowledge set (GDS) is catalogued because it’s created, and a most of 255 generations (the LIMIT worth) are retained within the GDG base catalog entry.

As soon as 255 datasets have been created, the GDG base entry is ‘full’ and the oldest technology should ‘roll off’ of the GDG and is deleted (SCRATCH). Optionally, if EMPTY is specified quite than NOEMPTY, all generations (not simply the latest) will roll off when the GDG is full.

The technology datasets belonging to the GDG above have dataset names of the shape MY.BUSINESS.DATA.G0001V00, the place the final qualifier (known as the ‘goovoo’ stage) specifies the absolute technology quantity – which can vary from 0001 to 9999 as generations are created, rolled off, and deleted. The model quantity (‘Vxx’) is never used. 

Whereas attainable to check with a selected technology dataset by its absolute title and model, it’s extra frequent to make use of relative technology numbers within the dataset title.

The relative technology is specified by inserting it in parentheses following the GDG base title.

The newest, or present technology, is technology zero – in our instance that is MY.BUSINESS.DATA(0).

• Older technology numbers are prefixed by a minus signal – so, the technology previous the present technology could be BUSINESS.DATA(-1)
• New generations are created by specifying a plus signal: BUSINESS.DATA(+1) and MY.BUSINESS.DATA(+2).

When creating new generations, be sure that to specify every new technology quantity in ascending order because the dataset names seem within the JCL, significantly in a multi-step job, in order that the generations are catalogued accurately.

Technology datasets are generally used not just for unusual enterprise purposes, however for system knowledge as nicely – significantly SMF knowledge. They’re particularly versatile, since any particular person technology dataset inside a GDG can reside on disk or tape, could be SMS-managed or non-SMS, and might have differing block sizes or different traits.

But, GDSs are simply and robotically managed by advantage of their naming conference. Generations are:

• Saved in chronological order
• Mechanically deleted as needed
• Referred to individually or as a gaggle

Processing All Generations

Whereas most day-to-day processing will in all probability take care of technology datasets separately, purposes that course of weekly or month-to-month could need to take care of the entire generations belonging to a GDG directly.

That is completed by merely specifying the GDG base title within the JCL, with none relative or absolute technology quantity. For instance:

//INPUT DD DSN=MY.BUSINESS.DATA,DISP=SHR

This ‘GDG-all’ processing treats the DD assertion as if it have been a mixed enter of the entire generations belonging to the GDG.

By default, the generations are processed from the latest to the oldest (LIFO order). They will, nevertheless, be processed from oldest to latest by specifying FIFO both when the GDG base is outlined or on the GDGORDER parameter within the JCL.

In more moderen releases of z/OS, IBM has continued so as to add options to GDG processing, together with LIFO order and using Prolonged GDGs which may hold monitor of as much as 999 generations quite than the earlier restrict of 255.

Extra GDG-related parameters have been added to the JCL language. Defaults for GDG DEFINE can now be set within the IGGCATxx member of SYS1.PARMLIB. As well as, customers of Exactly Syncsort Allocation Management Middle (ACC) can make the most of systemwide allocation requirements enforced by the ACC Coverage Guidelines Engine to set insurance policies for the creation and traits of not solely technology datasets, however all sorts of different SMS or non-SMS knowledge.

GDG: A Core Energy of z/OS

GDG processing is a singular energy of the z/OS system.

With little or no effort, a number of iterations of associated knowledge could be grouped collectively, tracked, and managed utilizing unusual batch job and catalog processing.

GDGs are easy to know and helpful for a variety of each enterprise and system knowledge. They’re typically the spine of a number of the most essential purposes that run on immediately’s z/OS.

To be taught extra and take the subsequent step past GDGs, see how Syncsort Storage Administration helps you optimize IBM Z storage and keep away from pricey space-related failures.

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