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Before a query or stored proc with a TVP starts executing, SQL Server creates a table in tempdb with the same schema as the parameter table type and uses bulk insert internally to efficiently load the table with TVP rows streamed by the client application.The size of a TVP is constrained only by available tempdb storage.The client application was run on a different machine than the database server and elapsed time measured by the application.The average duration was 113ms without a trace running when the app code used the default -1 max column length.All tests used the same table type of 10 varchar(50) columns and a 10,000 row TVP rows passed via a Data Table object of 10 string columns.The only variables were the max column length specified by the app code and a trace running on the database server.SQL Server executes the query/proc after the TVP temp table is loaded and the parameterized T-SQL query/proc can then use the TVP data.The TVP columns provided by the client application do not have to match the schema of the target table type; SQL Server implicitly converts TVP values to match the target table type column when data types differ.
Consequently, using the default Data Table column string data type for non-string types will: • increase client memory requirements compared to more compact native types • incur conversion overhead • prevent strong-typed data validation on client side • require date format aware formatting of date and datetime values • require using a period as decimal separators • increase network usage compared with smaller native types When String is the proper column data type, developers must be especially mindful of the max length specification when the Data Table is used as the TVP value. Avoid using long string columns in TVPs when many rows are passed and never use the default -1 length unless a MAX type is actually intended.
Although not optimal, implicit conversion is generally not a major factor in overall TVP performance.