Re: [Hardhats-members] BIG NEWS re HealtheVet- St. Petersburg Tim es

Thu, 14 Apr 2005 22:23:56 -0700

These are references to the internal structure of a Mumps database (globals) and it is not necessary to understand these in order to program Mumps.
 
Look here for definitions of b-tree, balanced tree, binary tree:
 
If you google "balanced tree" you will find lots of explanations. Ones with picture are probably the most helpful, like: www.cs.oberlin.edu/classes/dragn/labs/avl/avl5.html
 
Most Mumps implementations use some form of b-tree (there are many), BUT the Mumps global structure does not define a b-tree.  There still exist implementations that do not use b-trees. Fortunately, you will probably never encounter one!  The global structure is a simple hierarchical database.
 
Block splits (not pointer splits) occur when there isn't enough room to insert data into the appropriate block so some of the data in that block must be moved to a new (unused) block -- thereby "splitting" the old block in two.  The pointers which form linked lists of blocks must be adjusted to incorporate the new block.
 
 
 
----- Original Message -----
From: Ron Ponto
Sent: Thursday, April 14, 2005 11:29 PM
Subject: Re: [Hardhats-members] BIG NEWS re HealtheVet- St. Petersburg Tim es

For us new Mumpies could you explain what B-trees are and what is a pointer split? 
 
-------Original Message-------
 
Date: 04/14/05 23:23:45
Subject: Re: [Hardhats-members] BIG NEWS re HealtheVet- St. Petersburg Tim es
 
Actually there is.
 
   Most MUMPS implementations are multi-way B-trees.  Real true B-trees
suffer badly in real-life, nearly every action is a pointer split.  The
performance of MUMPS sparse arrays is in the shared buffer pools and broad
pointer structures that get you to any data location in a 1,000,000 element
database in 7 physical disk accesses or less.
 
  Best wishes;  Chris
 
----- Original Message -----
From: "Thurman Pedigo" <[EMAIL PROTECTED]>
Sent: Thursday, April 14, 2005 7:26 PM
Subject: RE: [Hardhats-members] BIG NEWS re HealtheVet- St. Petersburg Tim
es
 
 
> Back to Donald E. Knuth eh? One would think that by now... Guess there
isn't
> much new under the Sun. ..tx/t
>
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:hardhats-
> > [EMAIL PROTECTED]] On Behalf Of Greg Woodhouse
> > Sent: Thursday, April 14, 2005 6:14 PM
> > Subject: Re: [Hardhats-members] BIG NEWS re HealtheVet- St. Petersburg
Tim
> > es
> >
> > Of course, when you really get down to basics, it's all B-trees,
> > whether you're talking about MUMPS or your favorite RDBMS.
> > s-members
>
>
>
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