Have you ever encountered a situation where an IDENTITY column in your SQL Server database has overflowed its upper boundary? This can be a critical issue, especially if the table is central to a lot of processing. In this article, we will explore the concept of IDENTITY columns in SQL Server and discuss how to identify and manage them effectively.
What is an IDENTITY Column?
An IDENTITY column is a column in a SQL Server table that automatically generates a unique numeric value for each new row inserted into the table. It is commonly used as a primary key or an organizing ID for the table. The IDENTITY property ensures that each value generated is unique and incrementally increases with each new row.
The IDENTITY Crisis
Imagine a scenario where an IDENTITY column in a mission-critical backend database server overflows its upper boundary within a short period of time. This can lead to data integrity issues and potentially disrupt the functioning of the application. In such cases, it becomes crucial to identify and address the problem before it becomes a major concern.
In the example mentioned earlier, the author encountered a similar situation where an IDENTITY column had overflowed the integer datatype within just 8 months of its implementation. The column was only used as an organizing ID, which made the cleanup process easier. The author changed the column datatype to bigint, ensuring that the table would not face any problems for the next 6 to 9 billion years.
Identifying IDENTITY Columns
When dealing with a large database, it is essential to identify all the tables that have IDENTITY columns and check their current values and datatypes. Unfortunately, the INFORMATION_SCHEMA views do not provide direct information about the IDENTITY property of a column. However, there are alternative methods to retrieve this information.
One approach is to use the system stored procedure sp_help, which displays information about the IDENTITY column. By examining the code of sp_help, the author discovered that the IDENTITY columns can be found by querying the syscolumns and sysobjects system tables. This allowed the author to construct a query that shows the table name, column name, datatype, and current value of each IDENTITY column.
Managing IDENTITY Columns
Once you have identified the IDENTITY columns in your database, it is important to manage them effectively to avoid any future issues. Here are some best practices:
- Monitor the values: Periodically log the values of the IDENTITY columns to an audit table. This will help you project when the datatype might run out of “room” to represent the values.
- Focus on active tables: If your database has numerous IDENTITY columns, concentrate on the most active tables, especially those with the highest values. This will allow you to prioritize your efforts and address potential problems before they arise.
- Consider datatype limitations: Be aware of the datatype limitations of your IDENTITY columns. If you anticipate a large number of rows being inserted, consider using a larger datatype, such as bigint, to accommodate the future growth.
Conclusion
Understanding and managing IDENTITY columns in SQL Server is crucial for maintaining data integrity and preventing potential issues. By identifying IDENTITY columns and monitoring their values, you can proactively address any problems before they become critical. Remember to consider the datatype limitations and focus on the most active tables to ensure the smooth functioning of your database.
References:
- http://www.sqlservercentral.com/columnists/sjones/identityreset.asp
- http://www.sqlservercentral.com/scripts/contributions/65.asp
- http://www.sqlservercentral.com/scripts/contributions/1279.asp
Remember to regularly monitor and manage your IDENTITY columns to ensure the smooth operation of your SQL Server database.
Happy coding!