Re: Index Scans become Seq Scans after VACUUM ANALYSE

Oliver Elphick wrote:

>On Wed, 2002-04-17 at 06:51, mlw wrote:
>
>>I just think there is sufficient evidence to suggest that if a DBA creates an
>>index, there is strong evidence (better than statistics) that the index need be
>>used. In the event that an index exists, there is a strong indication that,
>>without overwhelming evidence, that the index should be used. You have admitted
>>that statistics suck, but the existence of an index must weight (heavily) on
>>the evaluation on whether or not to use an index.
>>
>
>But indexes are not, for the most part, there because of a specific
>choice to have an index, but as the implementation of PRIMARY KEY and
>UNIQUE.  Therefore the main part of your argument fails.
>
That is not my experience.  Wholly 3/4's of the indices in PeopleSoft, 
SAP, and Clarify (on top of Oracle 8 and 8i backends) are there solely 
for perfomance reasons, the remaining 1/4 are there because of 
uniqueness and primary key responsibilities.

In many of the cases where it is a primary key it is also there to 
ensure fast lookups when referenced as a foreign key.  Or for joins.