Will adding a nonclustered index lock my table?

Question

I have a table with ~2 million records in and I need to add a new nonclustered index to a uniqueidentifier to improve query performance.

Will adding a nonclustered index lock the table or otherwise degrade performance significantly while it's being applied?

There's lots of information out there about the benefits/pitfalls of indexing, but I can't find anything that tells me that happens during an indexing operation

I'm running SQL Server 2008 R2 (on Windows Server 2008 if that's important)

EDIT: It's the Enterprise Edition

Answer 1

For those of us not running "Expensive Edition" (Enterprise), the answer is thus:

An offline index operation that creates a nonclustered index acquires a Shared (S) lock on the table. This prevents updates to the underlying table but allows read operations, such as SELECT statements.

So basically it renders the target table "read only" while the index is built. This may or may not be a problem for your overlaying applications -- check with your dev teams and users!

PS: The question of whether or not, or why, to apply such an index, is an entirely different conversation. The SQL community and its legion of professional bloggers & SMEs are your friends.