Re: Encoded Vector Indexes -EVI's

[John P Carr <jpcarr@xxxxxxxxxxxx>]

>Hi Peter,
>Yes, they are only available through the SQL interface and, as such are
>read only (ie. you can't currently use them in RPGLE programs). I don't
>know enough about them to know what it takes to be able to perhaps include
>them in programs (eg. for insert or update or read) but they make a massive
>difference when using query/400. Very quick. The query optimizer
>automatically finds the relevant logical (EVI) to use.
>Ragards
>John Finney


" (ie. you can't currently use them in RPGLE programs)"

More exactly,  you can't use them(never will) in any program.  They,  Like
regular
SQL indexes really aren't specified in any program.   The Optimizer uses
them
in determining how to access the table.   It can use EVI's in conjunction
with regular
indexes and with bit maps (as previously noted) via XOR  & ANDs  .
It does keep track of how many destinct occurances exist for the specified 
key,  where the first occurance is and where the last occurance is.  Among
other things.

It is not however a  " Everywhere,  Everytime, for Everybody " type of
thing.  
They should be used where there is a relatively small number of distinct
values for example.

John Carr
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