Re: Creating Logicals before or after populating a file ?

[Larry Bolhuis <lbolhui@xxxxxxx>]

> 
> But what do you mean by "vining" ? Excuse my ignorance, the term rings a
> bell, but... ?

  When you add keys(Leaves) to an index tree they must attach to a
branch.  Each branch can attach a fixed number of leaves and branches.
When all the spaces are full one of the leaves gets plucked off and
along with the new leaf gets put on a new branch which is connected to
the previous branch where the leaf came from.  When a large number of
keys are added that have very similair (or even duplicate if allowed)
values the leaves get added in the same spot causing many branches to be
added in lower and lower levels.  Thus the tree lookes more like a vine,
hence the term.

  Vining makes processing the key very expensive.  So IBM has routines
in the key maintenance code that shift the tree around to minimize
Vining.  This takes lots of CPU and IO when it kicks in.

  Example insert:


before add
       ----------------------
       L  L  L  L  L  L  L  L

after add
       ----------------------
       L  L  !  L  L  L  L  L
             !      
-----------------------
          L  L

Larry Bolhuis
Arbor Solutions, Inc
lbolhui@ibm.net


> 
> Unfortunately it is not a multi processor system, so....
> 
> With reference to the other posts, I had a preference toward option 1, but
> wanted to be able to provide more explanation to the development team that
> developed the application.
> 
> Somehow or other in my 15 years on 38's and As/400's: F60.. sheesh... E60..
> D60... B60.. Sys/38 mod 700 .. 600.. 400 .... what about a Sys/38 7C1 with
> 4? 8? meg of memory ;) some of the lessons regarding logicals have become
> habit rather than being able to recall the reasons behind it.
> 
> If I could only convince these guys that 20 logicals may be excessive..
> they have large numbers of logicals built over everything !
> 
> Anyway, thanks again for all the posts.. a mine of information as usual.
> 
> Cheers
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