We all know that both operations, an index reorganization and update statistics in SQL Server, will not block normal DML statements on their own. (i.e. ANY SELECT, INSERT, UPDATE or DELETE). That said, I ran into a weird situation where I had a really simple query that did an index lookup using the primary key that usually takes milliseconds, but was for some reason running for over 10 minutes while executing during my index maintenance window. I looked at the output of sp_who2 and I confirmed that the index reorganization was at the head of my blocking chain. Let’s dig a little deeper and see if we can explain how this could happen.

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