Re: Index Advisor Recommending EVI

[Gord Hutchinson <gordm1@xxxxxxxxxxxxxxx>]

Thanks Eric.

I'm addressing the list from the most recommendations down.  This
particular one, the only EVI recommended, has been recommended over 600000
times (since day 1).

I've only recently been building indexes based on the advisor's
recommendations.


lkGord



On Wed, Mar 14, 2012 at 12:24 PM, DeLong, Eric <EDeLong@xxxxxxxxxxxxxxx>wrote:

> I would suppose that EVI recommendations come about if the SQL optimizer
> wants to use bitmap indexes, which are very efficient for record selection
> purposes.  Not useful for ordering, but not all queries need that...
>
> Part of the details associated with the index advise is how many times
> this recommendation have be made.  You get more benefit in optimizing the
> most used SQL statements, since these are what the CPU is spending time to
> process...  If your EVI has only been recommended once or twice, then it
> might not be worth the cost of storage to implement.
>
> Building the EVI per the recommendation does not ensure that the EVI will
> be used for a particular query.  It is quite possible that an EVI might
> wind up getting excluded for consideration due to other implementation
> requirements that only get tested if the EVI index actually exists.  There
> are no guarantees with the SQL optimizer...
>
> -Eric DeLong
>
> -----Original Message-----
> From: midrange-l-bounces@xxxxxxxxxxxx [mailto:
> midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Gord Hutchinson
> Sent: Wednesday, March 14, 2012 10:21 AM
> To: Midrange Systems Technical Discussion
> Subject: Index Advisor Recommending EVI
>
> How reliable are the Index Advisor recommendations for creating an EVI?
>
> I have a table which last Saturday had 622,804 rows with 60,922 distinct
> values of the key field for which the advisor is recommending an EVI.
>  Currently there are 61,752 distinct values out of 635,428 rows.
>
> This table grows by 20K to 30K rows per week.  There are also lots of
> updates and deletes to the table.
>
> This seems like a lot higher number of distinct entries than I've seen
> recommended for an EVI.
>
> Gord
>
> --
> Gord Hutchinson
> TST Overland Express
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