Re: Indexing data warehouses

Data warehouses ARE usually heavily indexed. Often indexes will take up more space on your disk than your data. Of course, this depends highly on your data (cardinality, table structure, etc). It is possible in Oracle for a full table scan to be faster than an index scan, esp if you don't know what the queries are going to look like.

The drawbacks of heavy indexing is that the indexes must be updated or rebuilt when your data is refreshed. This requires memory, temporary space and time.

gnilges_at_qni.com (Gary Nilges) wrote:
>I was told that data warehouses traditionally didn't have alot of
>indexes. I would think, though, that since this is a read-only OLAP
>instance with users pounding the heck out of it with a querey tool,
>that you'd want to index the heck out of it.
>
>What are the drawbacks (if any) to indexing in a read-only data
>warehouse? Was I told wrong, or are DW's usually not highly indexed?
>This is an Oracle 7 installation on an HP UNIX box, btw.
>
>thanks,
>
>...gary
>
 

-- 
 Michael DeVito                           Compuserve: 74634,3522
 Senior Database Administrator            AOL: MikeDeVito 
 Care Management Science Corp             voice: (215) 387-9401 
 Philadelphia, PA  19104                  messages: (215) 232-3326
 mdevito_at_chc.org                          fax: (215) 387-9406