On Feb 8, 2008 6:59 PM, Denys Beauchemin <[log in to unmask]> wrote:

> Mike is correct; MPE/iX uses prefetching and IMAGE is all mapped I/O.
> MPE/iX gets pages of data from disk in multiples of 4k byte blocks.  When


Look it up.  MPE/iX gets 2k physical blocks from disk, and packs 2 physical
blocks into 1 logical block of 4k.

Show me where HP uses the term "prefetch" to mean read-ahead or block read
or whatever.

HP uses the term "prefetch" extensively in respect to TurboImage.  It is
described as DBUTIL toggle-able feature for loading all database disk pages
into memory before issuing a lock for a DBPUT, DBDELETE, or CI DBUPDATE, to
minimize the lock's duration.  You must of skipped over some of my
verbosity.

Both Mike and Denys are therefore wrong! :-)

earlier I asked for a LISTF,2 of the master dataset, what I wanted to see
> was the record size.  This record size should be at 2048W or a factor
> thereof, like 512 or 1024.  This means that when MPE fetches IMAGE blocks
> (records,) it will bring in complete blocks at one time and be able to
> decipher them in memory.  It has been my contention for a long time now
> (15
> years?) the best record size for an IMAGE dataset is 2048W.  If you can
> fit
> multiple IMAGE records into on 2048W MPE record, you are doing yourself a
> favor.


Seeing as MPE/iX works with 4kB logical pages, this is elementary, my dear
Watson.

Until such time as we know the size of the master record and the size of the
> dataset record, all this discussion is for naught.


Some aspects are, others aren't.  Without having hardware specifications and
a performance profile of the system under a normal load, sizes aren't going
to tell you everything you need to know either.


> But it is entertaining.


Amusing and revealing too.

- Pete

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