AW: Question about Encoded Vector Indexes (EVI)

["HauserSSS" <Hauser@xxxxxxxxxxxxxxx>]

EVIs are supported and used by both query engines (CQE and SQE).
They also can be used by non SQL interfaces, like OPNQRYF or QUERY/400.

The query optimizer decides to use EVIs or binray radix indexes.
With an EVI you can get faster access to the data, but they cannot be used
to sort data.
It also cannot be used to join or group data.

"When the selected row set is relatively small, a binary radix index will
usually perform
faster access. When the selected row set is roughly between 20% and 70% of
the table
being queried, table probe access using a bitmap, created from an EVI
or binary radix index will be the best choice. Also, the optimizer and
database engine
have the ability to use more than one index to help with selecting the
data."
(from Indexing Strategies by Michael Caine)

Birgitta


-----Ursprüngliche Nachricht-----
Von: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx]Im Auftrag von Tony Carolla
Gesendet: Dienstag, 7. Juni 2005 06:38
An: RPG programming on the AS400 / iSeries
Betreff: Re: Question about Encoded Vector Indexes (EVI)


If you create SQL views, which basically become on-demand Logical files, and
then you use those views in queries, or even RPG, they can use EVIs. I do
this, and I don't have the SQL developer package. The trick is when to use
one of them, vs. a traditional index.

On 6/6/05, Karen L Hodge/MIS/Genesys <KHodge@xxxxxxxxxxx> wrote:
>
>
>
>
>
> I have just learned about the existance of EVI's and am really excited
> about what I have heard.
>
> Can anyone tell me:
>
> Is the improvement in performance limited to SQL and OPNQRY or will
> queries created in WRKQRY use the EVI?
>
>
> Thank you,
>
> Karen Hodge
> Senior System Analyst
> Genesys Health System
> 1000 Healthpark Blvd, Grand Blanc, Mi 48439
> Office 810.606.5180, Fax 810.606.7204
> khodge@xxxxxxxxxxx
>
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