Mainframes are totally different. They’re the most important, quickest, most succesful techniques on the planet, they usually nonetheless run many, if not most, of a very powerful functions within the business world.
One motive 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 take care of many alternative successive units of the identical kind of information. Every 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 bunch, within the desired order.
Because the early days of mainframes, the Technology Knowledge 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 whole assortment of datasets (a ‘GDG-all’) request.
This highly effective but easy technique of managing information is exclusive to z/OS.
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 slightly 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 discuss with a specific technology dataset by its absolute identify and model, it’s extra widespread 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 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 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 sure that 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.
Technology 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 may have differing block sizes or different traits.
But, GDSs are simply and routinely managed by advantage of their naming conference. Generations are:
- Stored in chronological order
- Routinely deleted as needed
- Referred to individually or as a bunch
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Processing All Generations
Whereas most day-to-day processing will in all probability take care of technology datasets separately, functions that course of weekly or month-to-month could need to take care of all the generations belonging to a GDG directly.
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 all the 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 newer releases of z/OS, IBM has continued so as to add options to GDG processing, together with LIFO order and using Prolonged GDGs which might maintain monitor of as much as 999 generations slightly 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 forms of different SMS or non-SMS information.
GDG: A Core Energy of z/OS
GDG processing is a novel 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 a number of the most vital functions that run on at this time’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 expensive space-related failures.
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