RE: Numerics PACKED, ODD format -- Always recommended?

[John Carr <74711.77@xxxxxxxxxxxxxx>]

RE:     RE: Numerics PACKED, ODD format -- Always recommended?

Booth, Walden
Its not the wasted bit thats the problem on even packed data, its the 
fact that after an arthimatic operation the machine does an integrity 
check on the unused high order bit to ensure it was not violated by the
operation.  It's the integrity checking that causes the performance hit. 
"I believe"

But (like on an 170 with a CPW of 319) we have much more important
things to worry about than the performance of that now. (and/or date type
performance !! I told yous guys a year ago they would make date types
perform better.)

Now about those 100+ I/O's per enter key.........

John Carr
EdgeTech
------------------
Booth,

In packed data the 9th character is free from a DASD point of view. That is
one of the reasons for the argument of going to the odd lengths. Think of it
this way:

8,0 field with value 12345678 is stored as x'012345678F' on the database (5
bytes)
9,0 field with value 123456789 is stored as x'123456789F' on the database
(still 5 bytes)

The argument is: since you need the last nibble to store the sign 'F' and
since all data must be byte aligned (at a minimum) you are simple wasting
the high order nibble going with a even length field.

-Walden

-----Original Message-----
From: mcsnet!midrange.com!midrange-l-owner@Mcs.Net
[mailto:mcsnet!midrange.com!midrange-l-owner@Mcs.Net]On Behalf Of Booth
Martin
Sent: Thursday, March 12, 1998 12:36 AM
To: MIDRANGE-L@midrange.com
Subject: Re: Numerics PACKED, ODD format -- Always recommended?


Bob Crothers wrote:
>
> Karen,
>
> Yes, it is best (from a performance point of view) to use odd
> length packed numeric data in your files.


Doesn't db/400 ignore the packed vs. zoned definitions now?  I thought
all numeric fields were packed regardless of what one writes in the dds.
About the odd vs even issue: if you need 8 characters, then you need 8
at least so you can't go to 7.  My understanding always was that the
cycles for 8 are the same price as the cycles for 9, so the 9th
character is a freebie, excepting dasd.
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