When a procedure is compiled for the first time or recompiled, the procedure's query plan is optimized for the current state of the database and its objects. If a database undergoes significant changes to its data or structure, recompiling a procedure updates and optimizes the procedure's query plan for those changes. This can improve the procedure's processing performance.
There are times when procedure recompilation must be forced and other times when it occurs automatically. Automatic recompiling occurs whenever SQL Server is restarted. It also occurs if an underlying table referenced by the procedure has undergone physical design changes.
Another reason to force a procedure to recompile is to counteract the "parameter sniffing" behavior of procedure compilation. When SQL Server executes procedures, any parameter values that are used by the procedure when it compiles are included as part of generating the query plan. If these values represent the typical ones with which the procedure is subsequently called, then the procedure benefits from the query plan every time that it compiles and executes. If parameter values on the procedure are frequently atypical, forcing a recompile of the procedure and a new plan based on different parameter values can improve performance.
SQL Server features statement-level recompilation of procedures. When SQL Server recompiles stored procedures, only the statement that caused the recompilation is compiled, instead of the complete procedure.
If certain queries in a procedure regularly use atypical or temporary values, procedure performance can be improved by using the RECOMPILE query hint inside those queries. Since only the queries using the query hint will be recompiled instead of the complete procedure, SQL Server's statement-level recompilation behavior is mimicked. But in addition to using the procedure's current parameter values, the RECOMPILE query hint also uses the values of any local variables inside the stored procedure when you compile the statement. For more information, see Query Hint (Transact-SQL).
This script generates for every stored procedure in a database een recompile statement
use [<database_name, sysname, your_database_name>]
concat('EXEC sp_recompile N''',schema_name(schema_id),'.',name,'''')
where type = 'P'