W dniu 2018-02-14 o 17:06, Pew, Curtis G pisze:
On Feb 14, 2018, at 9:47 AM, R.S. <[email protected]> wrote:
1. KEY
Nowadays there are two "datasets" using hardware key: VTOC and PDS directory.
What about other files? Is it possible to allocate new dataset with hardware
key?
According to JCL Reference, KEYLEN keyword can be used for VSAM KSDS or for
non-SMS datasets including BDAM, SAM, BPAM, QISAM (!) and EXCP datasets.
Is it still supported or just documentation is out of date?
My understanding is that the KEYLEN for a VSAM KSDS doesn’t refer the the CKD
hardware key.
That's obvious. VSAM does not use hardware key.
But why does it matter? Hardware keys are one of those “it seemed like a good
idea at the time” things that didn’t pan out. CKD hardware keys are extremely
slow and inefficient; you really don’t want to use them. IBM added the VTOC
index to avoid using the hardware key when searching the VTOC, and PDSE to get
away from the hardware keys in the PDS directory. Our lives would all be
simpler and better if we could actually eliminate hardware keys.
I just wanted to learn old things. Sometimes it helps to understand
current things.
As far as I know, the PDS directory consist of 256-byte blocks, but the 8-byte
key is not part of the block. Is it correct?
Or maybe it is 256 bytes including some 8-byte field which is repeated in Key
area?
The hardware key for a PDS directory block contains the name of the last member
whose entry is contained in that block. The 256 bytes is the data portion of
the block and does not include the 8 bytes of the key.
Thank you for your help.
Regards
--
Radoslaw Skorupka
Lodz, Poland
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