Re: Encoded Vector Indexes

["R. Bruce Hoffman, Jr." <rbruceh@xxxxxxxxxxxxx>]

----- Original Message ----- 
From: "Gerald Kern" <gkern@xxxxxxxxxxxxxxxxxxx>
To: <midrange-l@xxxxxxxxxxxx>
Sent: Thursday, October 23, 2003 19:17
Subject: Encoded Vector Indexes


> If I already have SQL indexes existing on my system, is there any notable
> reason not to replace them with EVI's?
>
> Since the system must already maintain the existing index, wouldn't the
> overhead associated with maintaining the EVI be somewhat similar to
> maintaining the existing index? The fields used to create the EVI would be
> identical to the existing index. The only difference is that it would be
> (re)created as an EVI. Wouldn't this be of benefit if it were only to
reduce
> the physical size of the index? (And I'd think the EVI would be faster
too).
> I'm running V5R2. Comments???


depends on why the index exists...

EVIs are, generally, only useful for selection. And only the optimizer can
use them. You can't open them and read them in a program.

They are used to provide a very fast way to select records based on the
cardinality of the column they are over.

Replace? Not unless the index was created just to provide statistics for the
selection of values from the column.


===========================================================
R. Bruce Hoffman, Jr.
 -- IBM Certified Specialist - iSeries Administrator
 -- IBM Certified Specialist - RPG IV Developer

"If you pick up a starving dog and make him prosperous,
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