Re: A question about Indexing.

From: a_blonde@mindless.com > > ---- you wrote: > > From: "Vijith Gunawardhana" <vijith.gunawardhana@wcom.com> > > > > > >In my work environment we are using Informix Dynamic Server AD and XP > > >Options 8.2. > > > > > >Here they don't use indexes at all. (Not even primary key indexes) > > > > > >1. Is that true if you access more than 15% rows of a table you don't >need > > >any indexes? (What about Group by / Order by?) > > > > This is always open to debate, but the reasoning for not having indexes >is > > largely as follows: > > > > * If you read more than a certain percentage of rows from a table, >indexes > > aren't used anyway (unless there's a sort). > > * In general, indexes are beneficial for sorting, but you need to weigh >up > > the performance benefit against the storage cost and the maintenance >cost > > (loads will be substantially slower). It may cost you too much load time >to > > justify the sort benefit. > > * By the time the data gets into the warehouse, it should be scrubbed >and > > validated, hence the lack of keys for RI. (This is the theory, anyway! >:-) > >Unless you speak to ex-RedBrick (now Informix) consultants Dude. They >insist a Data Warehouse needs RI! But that might be because they have a >star index, and ADO does not. Last time I looked, we were discussing the Database Server For Real Men With Hairy Chests (TM), not that wiffly other thing. :-) But (horror of horrors!) that chap Townsend from the O-word Corporation was basically right. When you're in AD/XP territory, the normal rules of database design don't really apply. I mean, ask any ex-RedBrick consultant how they would cope with putting RI onto a database where the _raw_data_ exceeded 2TB... :-) ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com