Hi Folks,
I was just involved in an exercise to improve an old file copying
program from CBT Tape File 316. It is called FFYCOPY, and it was
written in the mid-1970's by Frank Yates (courtesy of Jim Marshall).
This program's "copy engine" uses BSAM with double buffers, and for its
time, it was very fast, since BSAM (using the READ and WRITE macros)
deals with copying blocks of data instead of records. Of course, QSAM
(using the GET and PUT macros) is geared to copying records.
Most sequential file copying programs use QSAM, because the
granularity is at the "record" level and not at the "block" level. But
if speed is a priority, BSAM, copying equal sized blocks to equal sized
blocks, can be an advantage.
I'm not telling anybody here to give up the copying programs they
have been using (there are many of them out there), but this is for the
purpose of discussion, and I hope it helps somebody in the process
(maybe even me).
FFYCOPY, being a very simply written program (except for the skill
in writing the engine), needs to have the output dataset having
identical RECFM, LRECL, and BLKSIZE to those of the input dataset. To
guarantee that, it simply overlays those attibutes in the output dataset
before OPENing it. This may get into problems if you're copying a
sequential dataset to a member of a pds. The copy does not reblock the
dataset (as it uses BSAM very simply), and the output pds can be messed
up. To avoid such problems, I put safeguards into FFYCOPY (see FFYCOPY
in File 316 on the Updates page of www.cbttape.org), so that if RECFM,
LRECL, or BLKSIZE don't match, the copy is not done. I also added a
SYSPRINT dataset to report status of what happened. And to force the
overlay of the attributes in the output dataset (as in the old version),
you can code PARM=O in the EXEC statement.
I'd be interested in hearing if there are any issues nowadays in
copying BIG files FAST. Of course the world has progressed a lot in 40
years (snicker), but I'd still like to hear some thoughts on the subject.
Thanks much. All the best of everything to all of you.
Sincerely, Sam
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