Query Execution: Expectation-Reality

Yes, this is a widespread problem: you expect something, but the reality is a bit different. You assume that query will run 1 sec, but it runs (Oh, my God!) 1 hour. You expect that your query will perform an index seek, but it performs index scan instead. You know that your query doesn't use locks, but it uses them. Let's try to understand why this happens.

This session will focus on understanding the internals of such situations and making our expectations more close to reality. During the session, we will look at the queries which accidentally became slow, queries which can't finish and even queries which can't start and we will find the root causes for all those cases. And for each case, we will find the way how to handle that.