I know that I can't get a specific answer to my question, but I would like to know if I can find the tools to get to my answer.

Ok we have a Sql Server 2008 database that for the last 4 days has had moments where for 5-20 minutes becomes unresponsive for specific queries.

e.g. The following queries run in different query windows simultaneously have the following results

SELECT * FROM Assignment --hangs indefinitely

SELECT * FROM Invoice -- works fine

Many of the tables have non-clustered indexes to help speed up SELECTs

Here's what I know: 1) The same query will either hang indefinitely or run normally. 2) In Activity Monitor in the processes tab there are normally around 80-100 processes running

I think that what's happening is 1) A user updates a table 2) This causes one or more indexes to get updated 3) Another user issues a select while the index is updating

Is there a way I can figure out why at a specific moment in time SQL Server is being unresponsive for a specific query?