× The internal search function is temporarily non-functional. The current search engine is no longer viable and we are researching alternatives.
As a stop gap measure, we are using Google's custom search engine service.
If you know of an easy to use, open source, search engine ... please contact support@midrange.com.



Thanks Charles

Alan Shore
Programmer/Analyst, Direct Response
E:AShore@xxxxxxxx
P:(631) 200-5019
C:(631) 880-8640
"If you're going through Hell, keep going" - Winston Churchill


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Charles Wilt
Sent: Thursday, March 08, 2012 11:03 AM
To: Midrange Systems Technical Discussion
Subject: Re: Question about whether or not to create an Encoded Vector Index (EVI)

The redbook DB2-400 Mastering Data Warehouse Functions sg2458184 says:

This density factor is used by the Optimizer to favor the usage of indexes that have the highest density factor. The density factor becomes part of the calculations for data space I/O. Since the Optimizer can take advantage of this information, we recommend that you create EVIs (even in OLTP environment) for keys that:
* Have keys, which are naturally clustered For example, if the sales transactions are added daily to the file, the file is naturally clustered by sales date.
* Have keys, which were used in a sort to load the file

Consider also that it's SOP to have EVI's over the foreign key columns in your SALES_FACT table; one of which is usually a date key to the DATE_DIM.

So yeah, I consider Dates to be useful for EVI's

Charles

Charles

On Thu, Mar 8, 2012 at 10:21 AM, Alan Shore <ashore@xxxxxxxx> wrote:
I have just started reading about Encoded Vector Index (or EVI) One of
the points that seems to be stressed is cardinality as far as the key is concerned.
The states of the USA is good cardinality as there are only 50 of them.
Timestamps are bad, because you can have up to a kajillion of them.
How do you determine what is good and what is bad?
For instance, a date field (or at least a numeric field which represents a date), would that be considered a bad choice for cardinality.
Cardinality - I hope I have the correct word


Alan Shore
Programmer/Analyst, Direct Response
E:AShore@xxxxxxxx
P:(631) 200-5019
C:(631) 880-8640
"If you're going through Hell, keep going" - Winston Churchill


Disclaimer: This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission. If verification is required please request a hard-copy version. Any views or opinions presented are solely those of the author and do not necessarily represent those of the company.
--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing
list To post a message email: MIDRANGE-L@xxxxxxxxxxxx To subscribe,
unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx Before posting, please take
a moment to review the archives at
http://archive.midrange.com/midrange-l.

--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing list To post a message email: MIDRANGE-L@xxxxxxxxxxxx To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx Before posting, please take a moment to review the archives at http://archive.midrange.com/midrange-l.


As an Amazon Associate we earn from qualifying purchases.

This thread ...

Replies:

Follow On AppleNews
Return to Archive home page | Return to MIDRANGE.COM home page

This mailing list archive is Copyright 1997-2024 by midrange.com and David Gibbs as a compilation work. Use of the archive is restricted to research of a business or technical nature. Any other uses are prohibited. Full details are available on our policy page. If you have questions about this, please contact [javascript protected email address].

Operating expenses for this site are earned using the Amazon Associate program and Google Adsense.