At 8:19 +1000 6/4/04, John Pitman wrote:

>1.IIRC (sure to be corrected if wrong - Alfredo?), char keys hash better
>than integers in Image.

It all depends, of course ;-)

You might want to study Fred White's papers:
http://www.adager.com/TechnicalPapers.html



>All char strings in Image are fixed predefined
>lengths - does Varchar in oracle imply varying length? If so, this would
>impact searches and sorts.

John has, as usual, zoomed right into the kernel of an issue
that, more often than not, gets swept under the rug by
"marketing" ;-)

As a design choice, IMAGE "abstracts" (in the mathematical sense)
the "length" attribute of each dataset field ("column", if you
will) and maintains this "abstracted field length" in one place
(in the RootFile table for the corresponding data ITEM).  This
global (abstracted) data item length serves as the fundamental
unit to calculate a dataset's MediaLength (which you can consider
as the "integral" of all of its field lengths, including
chain-related privileged-mode fields in addition to user-mode
data fields that define the dataset's EntryLength).

This is one of the advantages of having "fixed length" entities
(or objects, or whatever) such as IMAGE dataset entries,
IMAGE dataset fields, MPE record-oriented files, etc.  As soon
as you start using "variable length" entities (or objects, or
whatever), you can't "abstract" the length attribute and you
must "carry it along" with its corresponding entity.  There is
a PERFORMANCE price to be paid for the benefits, if any,
associated with variable-length techniques.

So, Suresh, if the benefits of using variable-length entities
ARE better (for you) than the costs, then by all means use
such techniques.  Otherwise, why are you willing to pay the
performance penalties?  "Because such payments help the
marketing folks buy their fancy cars" is not acceptable ;-)

Getting ready for a healthy bike ride,

  _______________
 |               |
 |               |
 |            r  |  Alfredo                  http://www.adager.com
 |          e    |
 |        g      |  F. Alfredo Rego
 |      a        |  Manager, R & D Labs
 |    d          |  Adager Corporation
 |  A            |  Sun Valley, Idaho 83353-3000            U.S.A.
 |               |
 |_______________|

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