Execution plan is good, but not optimal.Compiled by each execution and requires CPU resources for every execution.Execution plan for every parameter combination.In the situation when most important parameter is known, the options is that we can optimize for that specific parameter with OPTION OPTIMIZE FOR: The price for improvement is paid all parameter combinations.To solve huge elapsed time for some combinations.Decomposition of SQL statement or decision tree to follow specific combination of parametersĪ) Using OPTIMIZE FOR UNKNOWN query hint:ī) Wrapping parameters in local variables:.Recompile execution plan every time when invoke stored procedure.There can be a few options/directions that we can go:
Stored procedure with recompile how to#
How to avoid side effect that is caused by parameter sniffing?: Second onvocation with Street and third with ZIP. Demo:Īll parameters are optional, at least one parameter must be provided.įirst invocation with BP number. It is not an issue, it is expected behavior. SQL server used the cached execution plan and performs a table or index scan, even if an index seek would be more efficient for this set of parameters. The same SP was called again with the different set of parameters that only returns a specified record. When as SP is executed for the first time, parameters that are passed required a large number of records to be read and query optimizer decided a table or index scan is the most efficient method to obtain the records. Optimal plan generated for the set of parameters on the first execution, does not have to be optimal for other sets of parameters. All subsequent executions reuse the execution plan from the procedure cache regardless if different parameters are passed. SQL server compiles the stored procedure using the parameter sniffing when the first time stored procedure is executed and put it in the plan cache. Queries submitted via sp_executesql stored procedure.Parameter values are sniffed for the following types of batches: SQL Server execution environment “sniffs” parameter values from the first invocation. The reason for this is very often so called “parameter sniffing”. The difference in the execution period can also occur if you execute stored procedure from the SQL Server Management Studio and from your application. Object ‘dbo.testt’ was successfully marked for recompilation.If you are writing a SQL queries or stored procedures, probably sometimes you noticed that stored procedure execution sometimes is quick and sometimes is slow. While this procedure is running in the above connection, open a different session and run the following command that forces recompilation and new execution. The current running procedures (that started before recompilation) still use the same old plan.Once recompilation is complete, it forces all new executions from then on to use new plan.Sql Server gathers all the meta data needed to generate optimal procedure plan based on the state of the database at that given time period.So, when a procedure is recompiled, it does not impact any of the procedures that are already in execution. One thing that became clear was, at any given time, several incidents of the same procedures are being executed by different application processes. For some reason, the cached procedure was becoming less efficient, even though it was not flagged as expired to be recompiled automatically. In one of those iterations, we ran into a peculiar situation, where we needed to recompile stored procedures every few hours. Of late, in our lab, we’ve been needing to run several performance tests (volume testing) to measure performance metrics under different load and traffic patterns. Interesting topic today: Does recompiling procedure stop current executions of the procedure?
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