Re: DWH : Index on Partition Key s
- From: Hemant K Chitale <hkchital@xxxxxxxxxxxxxx>
- To: Stephane Faroult <sfaroult@xxxxxxxxxxxx>
- Date: Sat, 31 Oct 2009 22:38:04 +0800
Stephane, Thanks for your response.Apparently in a partition for a month (uh oh !! : PARTITION_KEY='200910310000') , *all* the rows have the same PARTITION_KEY value.
Thus, a Month Partition has the same pseudo-date value stored in all the rows. So, the index is utterly useless.As for multi-column indexes, so far (in this design) I've seen them only for the Primary Key.
Other indexes are single-column indexes.Not even BitMap indexes on the FACT table --- had they been BitMaps, Oracle could have been doing an AND on the BitMaps.
This is an absolutely non-Oracle design on an Oracle database. The database is just a "data store".
Ugh ! Hemant Hemant K Chitale http://hemantoracledba.blogspot.com At 11:48 PM Friday, Stephane Faroult wrote:
Hemant, I don't see the point if you have any prefixed local index, but if you have none, if you have one partition by month and most queries hit a single day or less, then this index *might*, depending on volume, etc, etc. benefit those queries. But then perhaps you could begin to question the partition grain ... By the way a lot of developers seem never to have been told that you could index several columns at once. Or it's just the developers that work on the applications I have to audit. S Faroult