RE: Encoded Vector Indexes

["Gerald Kern" <gkern@xxxxxxxxxxxxxxxxxxx>]

99% of my SQL is used in embedded RPGLE and ORDER BY is often a requirement.
So the ORDER BY could be an issue where it is being used. But I do have a
few INDEXES that the SQL monitors recomended (that's why they were built in
the first place). My thought was that since they are built over one field
and are used for/by the optimizer only that they would be a better choice
for performance and storage reasons. But for places where an EVI was built
to replace an existing index (multi-key fields with order by implications),
would SQL sort the result set to accomodate the ORDER BY clause (if it used
an EVI)?

Thanks, Jerry

-----Original Message-----
From: Vern Hamberg [mailto:vhamberg@xxxxxxxxxxxxxxxxxxxxxxxxx]
Sent: Thursday, October 23, 2003 7:46 PM
To: Midrange Systems Technical Discussion
Subject: Re: Encoded Vector Indexes


Jerry, EVIs are a different kind of index, as you know. They cannot be used
for ordering records, only for record selection. This could be a reason to
keep the non-EVIs, if they are used to support an ORDER BY. Also, I don't
know whether and EVI index can be used in RPG, as a logical file can.
Certainly it would have unpredictable order.

EVIs are cool and performance is supposed to be better in V5R2 - there were
some problems earlier. No details, just scuttlebutt.

HTH

Vern

At 07:17 PM 10/23/2003 -0400, you wrote:
>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???
>
>Regards, Jerry
>
>Gerald Kern
>IBM Certified AS/400 RPG IV Developer & RPG IV Programmer
>MIS Project Leader, Lotus Notes/Domino Administrator
>The Toledo Clinic, Inc.