Multiple INSERT Statements vs. Single INSERT: When Does One Outperform the Other?

Multiple INSERT statements and single INSERT statement (including multiple VALUES clauses): Comparative performance analysis

In the performance comparison test of multiple INSERT statements and a single INSERT statement containing multiple VALUES clauses, the results were unexpected: although the latter is generally considered more efficient, the performance of multiple INSERT statements is better than that of a single INSERT statement INSERT statement.

To understand this phenomenon, it is necessary to analyze the execution plans of the two strategies. Planning of multiple INSERT statements uses a parameterization process to minimize parsing and compilation time. However, the situation changes significantly when the number of VALUES clauses in a single INSERT statement exceeds 250.

Compilation time surges

When there are more than 250 VALUES clauses, the SQL Server compiler switches from automatic parameterized plans to non-parameterized plans. This change can cause compilation times to increase dramatically. The compiler must perform sorting or similar operations when processing literals, resulting in a non-linear increase in compilation time.

The impact of string length and repeated values

Further experiments showed that longer string lengths can have a negative impact on compilation efficiency. In contrast, duplicate values ​​have a positive effect. When building algebraic expression trees, duplicate values ​​are identified, reducing compilation time.

Practical Application

This discovery has important implications for database design. When optimizing for a large number of inserts with unique values, it may be more efficient to use multiple INSERT statements with a parameterized procedure. On the other hand, if duplicate values ​​exist, a single INSERT statement with multiple VALUES clauses will perform better.

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