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Parameter Sniffing

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Plan Guides are like duct tape

Stabilizing Execution Plans: Plan Guides and NORECOMPUTE

Kendra Little
Execution Plans, Parameter Sniffing, SQL Server
14 Comments
What could go wrong? Sometimes you end up in a good plan / bad plan situation: an important query runs just fine most of the time. The query is parameterized, a good execution plan gets re-used, everything is cool. But sometimes, a “bad plan” gets compiled and starts to be reused. This is “bad” parameter sniffing. “Bad plans” can…
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Why You’re Tuning Stored Procedures Wrong (the Problem with Local Variables)

Kendra Little
Parameter Sniffing, SQL Server
20 Comments
There’s an important rule for tuning stored procedures that’s easy to forget: when you’re testing queries from procedures in SQL Server Management Studio, execute it as a stored procedure, a temporary stored procedure, or using literal values. Don’t re-write the statemet you’re tuning as an individual TSQL statement using local variables! Where it goes wrong…
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Optimize for… Mediocre?

Kendra Little
Parameter Sniffing, SQL Server
35 Comments
Some query hints sound too good to be true. And, unfortunately, usually they aren’t quite as magical as they might seem. Frustration with unpredictable execution times People often learn about parameter sniffing when query execution times stop being predictable. Occasionally you’ll hear about a stored procedure taking much longer than normal, but the next time…
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