Should You Use SET NOCOUNT ON in SQL Server?

SET NOCOUNT ON in SQL Server: Trade-offs

Whether to use "SET NOCOUNT ON" in SQL Server has always been a topic of debate among developers. Some see it as a performance benefit, while others warn of its potential drawbacks.

Background knowledge

The "SET NOCOUNT ON" command suppresses the "number of rows affected xx rows" message that appears after a DML operation. This message is a result set that the client must process, incurring a trivial but measurable overhead. In scenarios involving triggers or stored procedures, multiple "rows affected xx rows" messages can cause errors with some ORMs, including MS Access and JPA.

Supporters of SET NOCOUNT ON

Conventional wisdom holds that "SET NOCOUNT ON" should be used to improve performance. The argument is that since the "number of rows affected xx rows" message is unnecessary for most applications, suppressing it can reduce network traffic and processing time. Additionally, it is believed that SET NOCOUNT ON prevents errors in certain scenarios where the client expects a specific number of rows.

Opponents of SET NOCOUNT ON

Opponents of "SET NOCOUNT ON" argue that it may hinder advanced database operations. For example, suppressing row count information may interfere with:

• Use IF EXISTS to avoid duplicate records
• Use WHERE NOT EXISTS to limit results
• Filter out trivial updates
• Perform table access before or after DML operations

Additionally, SET NOCOUNT ON may cause unexpected behavior with some client frameworks (such as ADO.NET's SqlDataAdapter and JPA). These frameworks expect row count information, and its absence may lead to errors or incorrect results.

Performance impact

While it is commonly believed that SET NOCOUNT ON improves performance, the data suggests otherwise. In the TDS protocol, SET NOCOUNT ON saves only 9 bytes per query, while the command itself is 14 bytes. The "number of rows affected xx rows" message is not a separate network packet, but a small embedded structure. Therefore, the performance improvement is minimal.

Conclusion

Whether or not to use "SET NOCOUNT ON" depends on specific needs and considerations. It can be advantageous in scenarios where performance is critical or where the client framework does not rely on row count information. However, before implementing SET NOCOUNT ON globally, be sure to consider its potential drawbacks.

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