RE: logical file access paths

Eric

Thank you for your concise explanation, unfortunately you seem to have left
me
someway behind.

I will be ordering the books you recommended to-night.

Thanks again 

Colin.
   

> -----Original Message-----
> From: Eric N. Wilson [SMTP:doulos1@home.com]
> Sent: 13 April 2000 14:36
> To:   RPG400-L@midrange.com
> Subject:      Re: logical file access paths
> 
> The access path is a tree structure of sorts. The pointers to the
> individual
> records are at the bottom (leaf nodes) of the tree. When you change the
> key
> value of a record it removes the existing leaf node, inserts a new node in
> the appropriate place and then for both affected places potentially
> rebalances the branch above it until it reaches the point where it does
> not
> need to rebalance. The indexing technology that IBM uses is call a Binary
> Radix index for the indexes that you create in DDS. Note: There can be
> more
> than two nodes attached to any given node at a time. Eventually if you add
> or delete enough things will get rebalanced and you do not have to worry
> about degenerative tries...
> 
> Here is a link which contrasts EVI indexes vs. Binary Radix Indexes.
> http://www.as400.ibm.com/developer/bi/evi.html
> 
> If you are really really interested then there is a wonderful text written
> by Donald Knuth. "The Art of Computer Programming/Sorting and Searching."
> Right now the publisher has sold out (new edition which is being sucked up
> by all the geeks in the world :-) The whole three volume set is available
> though and I personally can not recommend it enough!!!
> http://www.amazon.com/exec/obidos/ASIN/0201485419/qid=955632533/sr=1-1/103
> -1
> 197673-3691861
> 
> The three books in this series will broaden any computer programmer's
> horizons and as Bill Gates said, "If anyone can read through these books
> then they should send me their resume." The is a lot of incredible
> information and these books are the most compact representation of
> distilled
> computer programming wisdom I have read.
> 
> I hope this helps
> Eric
> 
> 
> ______________________________________________
> Eric N. Wilson
> President
> Doulos Software & Computer Services
> 2913 N Alder St.
> Tacoma WA 98407
> 
> 
> ----- Original Message -----
> From: "Colin Thorpe" <Colin@IBS-PUBLIC-SERVICES.CO.UK>
> To: <RPG400-L@midrange.com>
> Sent: Thursday, April 13, 2000 1:13 AM
> Subject: logical file access paths
> 
> 
> > Thanks to all who responded to the original post....
> >
> > >The initial build has to read the entire file, build the key table,
> (Access
> > >Path), then sort the Access Path and write it to a file.  This initial
> read
> > >of the entire 10mil record file takes a while.
> Adding/Deleting/Updating
> > >record keys is done rather quickly on a record by record basis.  Don't
> you
> > >just love the power of the AS400s native data base.
> >
> >
> > A couple of points for clarity........
> >
> > 1. This is not a real issue, it is something we are discussing in our
> office
> > at the moment.
> >
> > 2. I understand the above but,
> >     If you change/update a record that is part of the key (ie
> order/access
> > path etc) why does it not have to
> >     rebuild the order/access path to accomodate this new record order
> and
> > therefore take some time.
> >
> > Thanks
> >
> >
> > Colin
> >
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