Understanding SQL Server’s Rowversion Data Type

SQL Server has a rich set of data types that can store various types of data. One such type is rowversion, which is also known as “timestamp” in some contexts, but not to be confused with the traditional datetime/timestamp data type.

What is rowversion?

rowversion is a data type that stores a relative timestamp for each row in a table. This value represents the timestamp at which the row was last modified or updated. Unlike traditional timestamps, rowversion does not account for clock time and is primarily used to track changes made to rows within a database.

How Does rowversion Work?

When you update a row in a SQL Server table, the system generates a new rowversion value based on the current timestamp at the moment of the update. This new value is then stored alongside the existing values for other columns in the row.

Here’s an example to illustrate this:

Suppose we have a simple table called my_table with three columns: id, name, and mr_timestamp.

CREATE TABLE my_table (
    id INT,
    name VARCHAR(255),
    mr_timestamp ROWVERSION
);

Let’s assume the initial values for our row are:

• id = 1
• name = 'John Doe'
• mr_timestamp = 0x000000001903A06C

Now, let’s update this row with a new value for name. The system generates a new rowversion value based on the current timestamp and updates the row accordingly.

UPDATE my_table SET name = 'Jane Doe' WHERE id = 1;

In this case, the updated mr_timestamp value might look something like this:

• id = 1
• name = 'Jane Doe'
• mr_timestamp = 0x00000001C123A06E

As you can see, the new rowversion value is different from the original value. This is because each update generates a new timestamp that represents the moment at which the row was last updated.

The Importance of Using rowversion

So, why would we want to use rowversion instead of traditional timestamps? There are several reasons:

• Avoiding Clock Time Conflicts: When using traditional datetime/timestamp data types, conflicts can arise when dealing with multiple clocks (e.g., different time zones). rowversion, on the other hand, is based on relative timestamps that don’t account for clock time, reducing these conflicts.
• Improved Sorting and Indexing Performance: Since rowversion values are not necessarily sequential, traditional sorting and indexing strategies may not work efficiently. However, SQL Server can optimize its internal workings to take advantage of the unique nature of rowversion, leading to better performance in certain scenarios.

Deprecation of timestamp Data Type

As mentioned earlier, the timestamp data type is actually an alias for rowversion. While it’s still supported for compatibility reasons, it’s generally recommended to use datetime or datetime2 instead. This is because these newer types are designed with better performance and compatibility in mind.

Conclusion

In this article, we’ve explored the SQL Server rowversion data type, which provides a unique way of tracking changes made to rows within a database. We’ve discussed its differences from traditional timestamps and highlighted some key benefits it offers. Additionally, we’ve touched on the deprecation of the timestamp data type and encouraged the use of newer alternatives like datetime or datetime2. By understanding how rowversion works and when to use it effectively, developers can create more efficient and reliable database applications.

Last modified on 2025-01-30