How much performance hit if I create index on all columns.

Let's say I have a table with 20 columns and index on each column.

How much peformance/overhead with and without indexes?

Thanks,
Veera

It depends... If you do mostly queries like in a data warehouse, it is beneficial to create all possible indexes. If you have more of an OLTP workload, you only want to create the indexes that you really need due to the added index maintenance overhead.

Furthermore, I wouldn't simply create indexes on all columns. It may be better to have an index on a combination of columns and you may not need indexes on some columns. Therefore, a good start would be to run your SQL statements as workload through the Design Advisor and see what indexes are suggested by that tool. The next step is to understand how indexes work (e.g. what is index-only access, prefetching, include columns, just to name very few) and then apply this knowledge to your workload.

Big hit, and you probably want some composite indexes and not just indexes with one column. Probably less than 5 of the indexes will ever be used by DB2, but DB2 will have to maintain them on inserts, updates, and deletes.