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OPTIMIZE FOR vs Forced Plans in SQL Server

Erik Darling makes a comparison:

I often see clients using forced plans or plan guides (yes, even still, to this day) to deal with various SQL Server performance problems with plans changing.

There’s usually an execution plan or two floating around that seems to be a good general idea for a given query, and a couple weird high-end and low-end outliers for very specific populations of values.

Read the whole thing, of course.

In defense of plan guides, the company I used to work for had a few—maybe three or four in total—because of really weird data skew problems on database 106 out of 700 (or so)—because there’s always one customer that makes wildly different use of the system than everyone else. And so a query that worked perfectly fine for 699 databases (or so) flops like a fish out of water for this one database with this one customer’s data in it. So the plan guide was a nicer expediency than optimizing for mediocre on all 700 (or so) databases.

One Comment

  1. Erik Darling
    Erik Darling2024-05-23

    Ha ha, optimize for mediocre is usually reserved for optimize for unknown mockery. Optimizing for specific values is a bit different, though I do admit that a couple of the outlier plans in my post are still rather mediocre.

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