How many database indexes is too many?

Question

I\'m working on a project with a rather large Oracle database (although my question applies equally well to other databases). We have a web interface which allows users to

Answer 1

In data warehousing it is very common to have a high number of indexes. I have worked with fact tables having two hundred columns and 190 of them indexed.

Although there is an overhead to this it must be understood in the context that in a data warehouse we generally only insert a row once, we never update it, but it can then participate in thousands of SELECT queries which might benefit from indexing on any of the columns.

For maximum flexibility a data warehouse generally uses single column bitmap indexes except on high cardinality columns, where (compressed) btree indexes can be used.

The overhead on index maintenance is mostly associated with the expense of writing to a great many blocks and the block splits as new rows are added with values that are "in the middle" of existing value ranges for that column. This can be mitigated by partitioning and having the new data loads aligned with the partitioning scheme, and by using direct path inserts.

To address your question more directly, I think it is probably fine to index the obvious at first, but do not be afraid of adding more indexes on if the queries against the table would benefit.