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Using Query Store over the Plan Cache

Erik Darling has a dream:

I used to think the plan cache was so cool.

– You can find queries that aren’t good there
– Plans are full of details (and XML)
– Supporting DMVs give you extra insights about resource usage

But most of the time now, I’m totally frustrated with it.

It clears out a lot, plans aren’t there for some queries, and the plans that are there can be very misleading.

Can you really tell someone what their worst performing queries are when everything in there is from the last 15 minutes?

No.

Read on for what’s nice about Query Store, as well as a few fixes which need to be there before it’s really useful. I’ve used Query Store in big environments to good effect (though our DBAs had to rewrite the cleanup processes because they’re bad) and I’ve had to turn it off in medium-sized environments running 2016 because it was harming performance. It’s a great concept and reasonable implementation with a few too many sharp edges.

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