Paul Gilmartin wrote:
On Tue, 27 Jul 2010 12:26:50 +0200, R.S. wrote:
Steve Comstock pisze:
Barbara Nitz wrote:
[...]
PDSEs have only one advantage: They don't need to get compressed. The
rest us a huge amount of disadvantages.
Regards, Barbara
And, I believe, multiple members can be written concurrently (I
believe; am I right?) How would one do this? Must one OPEN two or
more DCBs, one for each member being written? And one might yet
wish to be able to append or update in place existing members.
Well, they do have at least one other advantage: they can store
program objects, which allows entry points with long, case-sensitive
names, which is sometimes handy.
Steve, why would you call that an advantage? I thought you despise
case-sensitivity.
I do. But in some environments (e.g., DLLs, C, C++) it is a fact of life.
If you want to port / use applications from the z/OS world it is good
to have the ability.
Anyway, old fashioned PDSes allow case-sensitive
(but not long) member names; it's merely higher level interfaces that
try to conceal the case-sensitivity.
Ah, good point. I'd forgotten that, since the interfaces I work
with day to day are exactly of that type.
Would you advocate supporting
case-insensitivity at the DFSMS layer, similar to Windows? Mac OS X
gives the programmer a choice with a granularity of volume.
Not sure on that one.
While I could provide more PDSE advantages than Barbara, I would not
mention long names.
Reason: I HAVE NEVER SEEN AN APPLICATION WHICH USES THEM. Long names are
not handy for me. Of course I know, there are some... but not in
operating system components.
Isn't this a solution seeking a problem? What interfaces support them?
Surely, one can't code // EXEC PGM=Case-sensitive-Long-name? What about
ATTACH EP=Case-sensitive-Long-name?
Well, you can call DLL entry points from Assembler, COBOL, C, and PL/I.
But you can't invoke them from JCL, that's true. Nor can you LOAD,
XCTL, or ATTACH to long entry points. But several bpx.... services can
access a long, mixed case, entry name. I admit, it's a stretch. The
average day-to-day application programmer does not have a need / use
for this feature, at least not today, and one has to work at it to be
able to use it.
What's the format of the word returned by NOTE for a PDSE. It's
been discussed here that the low 24 bits contain the relative
record number within a member (biased by 0x100000). Do the top 8
bits then identify the member? What happens, then, if a programmer
performs BLDL for 257 different members? can the NOTE words
identify connections to all? If one performs 2 BLDLs for the
same member, are the two returned pointers identical?
How do Unix directories compare?
o They don't need to be compressed.
o Multiple members can be written concurrently.
o Members can be appended or updated in place (with a granularity
of byte.).
o They support long case-sensitive names.
o They allow a mixture of program objects and other member types.
Deficiencies:
o Alias entry points are not supported (AFAIK).
o The BPAM support is read-only (so far).
Questions:
o How do performance and reliablity compare with PDS[E]? I suppose
there might be four answers, separate for PDS vs. PDSE and for
HFS vs. zFS.
o What is the limit on member size?
o What is the limit on number of members?
-- gil
Well, I've been getting more and more into the z/OS UNIX world,
and I think you've raised some good questions / concerns here.
But based on a thread last year (or was it two years ago), there
seems to be precious little management interest in, or support for,
developing new applications using z/OS UNIX, and the systems folks
on ibm-main are certainly not big fans (for the most part, anyway),
eh Barbara?
--
Kind regards,
-Steve Comstock
The Trainer's Friend, Inc.
303-393-8716
http://www.trainersfriend.com
* To get a good Return on your Investment, first make an investment!
+ Training your people is an excellent investment
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