The Data Warehouse runs on a computer that serves other users and applications. You might experience poor performance when your job is competing for computer resources with other large jobs. Optimizing the Data Warehouse for fast response time is tricky because you are allowed to construct ad-hoc queries, i.e. use any field from any table. There is no way to identify indexed fields by looking at a table with GQL, Brio or Microsoft Access, so we have compiled a Listing of Indexes for your reference. Fields were picked based on limited users' observations of which fields are most likely to be used in queries.
Indexes take time to build and update every month when new data are added to the table.
Indexes also use up database space. So the secret to keeping you happy with fast queries and fast data loads is to index those fields commonly used in limiting queries, and accept that occasional queries will not be able to use any of those indexes and so will take longer. This is the bad news. Just because you include a limit on an indexed field does not mean the database will use that index. Always start with a small set before asking for the whole thing.