On Fri, 24 Apr 2009 07:15:15 -0500, Chase, John <jch...@ussco.com> wrote:
>> -----Original Message-----
>> From: IBM Mainframe Discussion List On Behalf Of John McKown
>>
>> [ snip ]
>> . . .. Take a case in point. A programmer has two VSAM KSDS
>> files. He is reading one file sequentially and wants to see in the
>second
>> file has as associated record in it (both files are keyed
>identically). How
>> to do that? I will grant that in the past, this was a "no brainer".
>However,
>> this "normal" (perhaps sub-normal?) programmer did it the "easy" way.
>He
>> read the first file sequentially. Then, for each record read, he did a
>keyed
>> read of the second file. The second file contained about 5% of the
>number of
>> records in the first file. So 95% of the time, the keyed read got a
>"record
>> not found" and, as a plus, ended up with its buffers flushed and
>positioning
>> lost.
>>
>> Of course the correct way to do this is to read each file sequentially
>in
>> parallel (they are in the same order due to using the "same" key
>values),
>> doing a "match merge" type operation. But that mindset seems, at least
>> around here, to have disappeared. I did the "match merge" code to show
>how
>> to do it (with a dramatic reduction in CPU and elapsed time). The
>programmer
>> considered __that__ to be "too advanced" and "obscure".
>
>IBM already provides a program to do exactly that: ICETOOL.
>
>Syncsort provides a similar program. Don't know about CA-Sort.
>
>Why bother to reinvent that wheel?
>
> -jc-
I simplified too much. The code was more like (pseudo-COBOL):
read master-file
perform until eof-on-master-file
move master-key to second-key
read second-file key second-key
if record-not-found-second then
.... do default processing
else
.... do processing based on data in second-file
end-if
read mater-file
end-perform
it is still "better" (personal opinion) to read both files sequential,
matching the key values and doing the required processing.
--
John
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