Re: BLOCK(*YES) questions

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

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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