What’s In a Title? Mainframe GDGs Get the Job Completed

Mainframes are completely different. They’re the biggest, quickest, most succesful programs on the planet, and so they nonetheless run many, if not most, of a very powerful functions within the business world.

One cause mainframes stay dominant? Their lengthy historical past of successfully coping with enterprise information.

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

For the reason that early days of mainframes, the Era Information Group (GDG) has been the technique of managing these successive occurrences (or ‘generations’) of the identical information. Just by utilizing the dataset identify, functions can choose a present or prior technology, create new generations, or use the complete assortment of datasets (a ‘GDG-all’) request.

This highly effective but easy technique of managing information is exclusive to z/OS.

Tips on how to Create a Mainframe GDG

Earlier than the person datasets that comprise a GDG might 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 atypical sequential datasets, might be created.

A DEFINE assertion, just like the one under, accomplishes a couple of 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 information 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 reasonably than NOEMPTY, all generations (not simply the newest) 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’) isn’t used. 

Whereas potential to seek advice from a specific technology dataset by its absolute identify and model, it’s extra frequent to make use of relative technology numbers within the dataset identify.

The relative technology is specified by putting it in parentheses following the GDG base identify.

The latest, 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 can 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 certain to specify every new technology quantity in ascending order because the dataset names seem within the JCL, notably in a multi-step job, in order that the generations are catalogued appropriately.

Era datasets are generally used not just for atypical enterprise functions, however for system information as effectively – notably SMF information. They’re particularly versatile, since any particular person technology dataset inside a GDG can reside on disk or tape, might be SMS-managed or non-SMS, and might have differing block sizes or different traits.

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

• Stored in chronological order
• Routinely deleted as needed
• Referred to individually or as a gaggle

Processing All Generations

Whereas most day-to-day processing will most likely cope with technology datasets separately, functions that course of weekly or month-to-month could need to cope with the entire generations belonging to a GDG without delay.

That is completed by merely specifying the GDG base identify 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 had been a mixed enter of the entire generations belonging to the GDG.

By default, the generations are processed from the newest to the oldest (LIFO order). They’ll, nonetheless, 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 the usage of Prolonged GDGs which might maintain monitor of as much as 999 generations reasonably than the earlier restrict of 255.

Further 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 benefit from 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 varieties of different SMS or non-SMS information.

GDG: A Core Energy of z/OS

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

With little or no effort, a number of iterations of associated information might be grouped collectively, tracked, and managed utilizing atypical batch job and catalog processing.

GDGs are easy to grasp and helpful for a variety of each enterprise and system information. They’re typically the spine of among the most vital functions that run on in the present day’s z/OS.

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

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