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Stats IO Oddities

Josh Darnell collects a few cases where SET STATISTICS IO ON doesn’t behave quite as you might expect:

The first one comes from a post on Database Administrators Stack Exchange: STATISTICS IO for parallel index scan

To summarize the situation, the OP had a query that was scanning a clustered index. They were seeing significantly higher numbers reported in the logical reads portion of the STATISTICS IO output when the query ran in parallel vs. serially (with a MAXDOP 1 query hint). There is a demo of this behavior in the post, so I won’t reproduce it here.

There are several interesting cases in here, so check them out.