RE: Blocking I/O (was: Expensive op codes)

["Dan Bale" <dbale@xxxxxxxxxxx>]

I don't spend a lot of time reminiscing of my days on the S/36, but the one
thing I miss and can't believe that the AS/400 never took advantage of was the
ability of the S/36 to block records on update files.  Not only that, but the
S/36 also took advantage of the double buffer option on the F-spec.  I
benchmarked all this way back when.  If I remember correctly, an updated record
in the buffer not yet written out to disk was still available to other jobs;
can't remember if the OS forced the write to disk or not.  Was this what was
referred to as "single level store"?

Your method of using an input file and an output file (with blocking on both)
instead of a single update file is a design that I've used before when faced
with a mass update of a very large file.  It's just a shame that, for whatever
reason, IBM couldn't port that S/36 feature over to the AS/400.

- Dan Bale

Joel Fritz wrote:

I work in a shop that does a lot of mailing list processing that involves
files with between 1 and 8 million records.  Preparing a list involves a lot
of updates to the information that doesn't pertain to the name and address.
Our standard has been for many years sequential I/O writing the output to a
clone of the input file.  We generally use forced blocking with OVRDBF as
well.  I haven't benchmarked the process recently, but it seems to me that
two machines ago, sequential I/O made the process more than twice as fast.
Since the original file is ordered (not indexed) it allows comparisons with
other ordered files without using random I/0 by means of a simple linear
search.  The really scary thing is that reading all the records in two 2
million record files can be faster than reading all the records in one and
doing keyed lookup on the other.





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