Re: COBOL Compiler for Windows



"Howard Brazee" <howard@xxxxxxxxxx> wrote in message
news:nhce14purq6ud3pk76qmg5hgtc15torruo@xxxxxxxxxx
On Tue, 29 Apr 2008 10:13:48 -0400, Graham Hobbs <ghobbs@xxxxxxxxxxx>
wrote:

I semi-expected your comments about CICS and DB2 but what's the
difference between KSDS and Indexed Sequential? For that matter what's
the diff between ESDS and 'flat or sequential' files?

I really should know this stufff but I don't!

GOOGLE is your friend...


It depends on the system. VSAM is a file management system that was
supposed to replace the three types of files that IBM already had on
mainframes (flat, indexed, and relative). In my experience it made
them more like the Univac 9030 file systems I was familiar with at the
time.


VSAM (the Very Silly Access Method) was a major leap up from ISAM (the
Incredibly Silly Access Method). The main enhancement was that VSAM was self
reorganizing and space managing. This eliminated problems like second level
overflow which previously degraded performance.

Difference between Indexed Sequential and VSAM/KSDS? Pretty much what I
just said. KSDS (Keep Spinning Don't Stop) was able to utilize the new VSAM
technology to assist with Index and Data organisation, Control Area and
Interval splits when more space was needed, and no need for a separate
Utility to reorganize. (Except that, in practice, IDCAMS (It Doesnt
Contribute Anything. Mostly Silly) is needed to reload datasets regularly,
or performance degrades just as it always did...)

IDCAMS is the utility to run this file management system. But
people were already familiar with the non-managed systems, and the
only place I've seen ESDS files was where I implemented them myself -
to replace the 9030 functionality.

ESDS (Entirely Superficial Data Storage) was fine for data entry, where you
could lose the odd item and re-enter it later, retrieval speed wasn't a big
priority and sequence wasn't a problem, but if you needed to find something
in a hurry, the last member of the VSAM family, RRDS (Really Righteous Data
Service), was the best. Unfortunately,figuring out the hashing algorithms to
make it work effectively, was a bit beyond the average programmer, so it
languished in a cupboard gathering dust...I once wrote an entire access
system based on it and everyone was very impressed... Dunno why, it was only
COBOL... :-)


On the other hand, KSDS files had some significant performance
advantages over IBM's previous indexed file system, so it became the
standard in most shops. (Many shops have replaced visible KSDS by
databases (which sometimes use KSDS behind the scenes)).


Someone who works with alternative mainframe company's machines just
see different flavors of indexed files. Their companies didn't come
up with new names for their improvements in file handling.

Sometimes they not only came up with new names but actually used different
access methods entirely. Everyone knows about "Indexed Sequential"... ever
used "Indexed Random"?

It was a really cool idea and I was blown away when I first encountered it.
Did everything Indexed Sequential did, but in less than half the time.
Perfect for online systems which were just starting to appear when it was
invented. It was multitasked and certain housekeeping functions ran in the
background without affecting performance in the foreground. It was developed
by Burroughs (the Unisys power of two that WASN'T Univac) and caused me to
realise (to my horror) that all the good IT ideas DIDN'T come out of IBM...
:-)

Pete.
--
"I used to write COBOL...now I can do anything."


.

Relevant Pages

  • Re: VSAM Internals
    ... I'm always interested in helping tune a "troublesome file", ... the MAP facility is from a Mainstar program called VSAM ... MAP does indeed show you the "insides" of any KSDS, ... For IBM-MAIN subscribe / signoff / archive access instructions, ...
    (bit.listserv.ibm-main)
  • Re: Dups In KSDS,ESDS
    ... Is there a standard way to handle "dups" if found in a KSDS, or an ESDS? ... KSDS is a keyed dataset, and by default CANNOT have a dupe, as it would ... ESDS is a non-keyed dataset, and as such has no true dupe, unless ...
    (bit.listserv.ibm-main)
  • Re: MAINFRAME SHOP STANDARDS (VSAM)
    ... >>VSAM pretty much duplicated what was available on other computers. ... I worked on many other mainframes around this time (IBM and the ... That's because using QSAM files in CICS is ... It's still a good idea to reorg VSAM KSDS files periodically, ...
    (comp.lang.cobol)
  • Re: COBOL Compiler for Windows
    ... the diff between ESDS and 'flat or sequential' files? ... KSDS files had some significant performance ... standard in most shops. ...
    (comp.lang.cobol)
  • Re: embedded SQL in COBOL
    ... a good understanding of both ESDS and KSDS ... at all between the Codd and Date relational model and "flat" VSAM files. ... necessary and essential to designing a database when using an RDBMS. ... the effective use of an RDBMS allows a bit more creativity ...
    (comp.lang.cobol)