The art of tuning is to understand not only the application but the platform
on which it runs. First optimize you blocks to use as much of the data as
possible. The Image manual has a section devoted to this. Something about
record size, bit area for number of records and the like. Once you have
packed as efficiently as possible the records, then it is on to the
hardware. To keep things simple I/O is done in 4096 byte blocks. So find a
multiple of your blocking factor which will effectively use this. Of course
some people just use the defaults, others max it out. Depending upon you
needs and dispersion of data within the table is the method you use. It goes
against logic to create a max block which would allow for 40 records, and
only read 1 record. But there is hope. If the system always reads 4096 bytes
then who cares what logic says. I has been my experience that if you are
reading 4096 bytes and 40960 bytes, even though it is 10 times more data, it
makes little difference to the I/O system. Again, if your are reading 1000's
of records strewn all over the disc, reading 40960 when you only need 40
will begin to tell on the I/O system. Then it is better to look into
grouping the data better. It is the finding the data that is the time killer
here. Once found get as much NEEDED information as possible, and you will be
surprised what that little tuning can do for your app.

James

-----Original Message-----
From: HP-3000 Systems Discussion [mailto:[log in to unmask]]On
Behalf Of Simonsen, Larry
Sent: Friday, December 10, 1999 11:02 AM
To: [log in to unmask]
Subject: turboimage and blockmax


Trying to understand the blockmax setting in TurboImage/XL a little better.
From what I have gleaned from reading I find this.

MPE/ix reads in chunks of 4096 bytes called pages or 16 sectors.
Turbo image stores in blocks as large as blockmax but may be smaller but
always a multiple of  256 bytes.

What happens when multiple TurboImage blocks will fit in a 4096 page?
What happens when a block spans a page, i.e. block size of 640 bytes.  The
first 3 blocks fit into the first page and then the next block has part in
one page and part in the next page?
Should blocks be made to be an integer fraction of a whole block?
Can blockmax be made 4096?
What should I be optimizing?

-------------------------------------------------
Larry Simonsen                Phone: 801-489-2450
Flowserve Corporation     Fax: 801-491-1750
PO Box 2200                    http://www.Flowserve.com
Springville, UT 84663      e-mail: [log in to unmask]
-------------------------------------------------
All opinions expressed herein are my own and reflect, in no way, those of my
employer.