Month: June 2016

How TOP wrecks performance (part 2)

In my previous post, I showed how the vanilla version of TOP can really help performance by nudging the optimizer into picking an execution plan that is optimized for returning just a few rows instead of the entire result set. But I also showed that adding WITH TIES causes a cardinality misestimate, which may lead to suboptimal or downright terrible plan choices. Luckily, this is fixed in SQL Server 2014 and later, provided you use the new cardinality estimator. In this post I will show how the PERCENT option causes even worse performance, and how you can avoid that performance…

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