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On Saturday, February 28, 2004, at 09:17 AM, Dan wrote:


So, physically, records by key can be all over the file, but BLOCK(*YES) on a
keyed file puts them in the buffer in key sequence. If the system has to jump
all over the disk to build this buffer, is there really any time savings?

Yes. Run your own timings to find out. You should see: No blocking - fast enough Keyed blocking - faster Sequential blocking - faster still Double buffering - fastest

For keyed blocking you won't gain any benefit from the DASD to main storage transfer but you will gain from the main storage to program buffer transfer. That's where reorganising the file in keyed sequence helps because it allows you to process sequentially by key and use double buffering.

Another question: Does the RPG program get control of the buffer after the
first record is put in the buffer by the system, or does the RPG program wait
until the system fills the buffer?

You are doing blocking so the system transfers a block of records to your program therefore you get them all at once.


This is an eye-opener. A colleague told me today that the BLOCK keyword for
the F-spec has been around since v3r7! That one must have flew underneath my
radar when it came out.

Actually VRM320 and VRM360.


Regards,
Simon Coulter.
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