Digging Into Batch Mode And Parameter Sniffing

Erik Darling has mixed news on the efficacy of using batch mode for rowstore as a way of eliminating problems arising from parameter sniffing:

SQL Server 2019 introduced batch mode over row store, which allows for batch mode processing to kick in on queries when the optimizer deems it cost effective to do so, and also to open up row store queries to the possibility of Adaptive Joins, and Memory Grant Feedback.

These optimizer tricks have the potential to help with parameter sniffing, since the optimizer can change its mind about join strategies at run time, and adjust memory grant issues between query executions.

But of course, the plan that compiles initially has to qualify to begin with. In a way, that just makes parameter sniffing even more frustrating.

Read on for both the good and the bad.

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