10 SQL Server Stored Procedure Error Handling Best Practices

Stored procedures are a vital part of any SQL Server database. They can help improve performance and maintainability, and can also make complex tasks much simpler.

However, stored procedures can also be a source of errors, which can be difficult to track down and fix. That’s why it’s important to follow best practices for error handling in stored procedures.

In this article, we’ll discuss 10 best practices for SQL Server stored procedure error handling. By following these best practices, you can avoid common errors and make your stored procedures more robust.

1. Use SET XACT_ABORT ON

When a stored procedure is running under the control of a transaction, and an error occurs, the default behavior in SQL Server is to ignore the error and continue processing. This is not always what you want, especially if the error is severe enough that it should cause the entire transaction to be rolled back.

When SET XACT_ABORT is ON, and an error occurs, the whole transaction is aborted and rolled back. This is usually what you want, because it means that any data that was modified by the stored procedure will be reverted to its original state.

There are some exceptions where you might not want to use SET XACT_ABORT ON. For example, if you’re using a stored procedure to update multiple rows in a table, and one of the updates fails, you might want the other updates to continue, so that the data is not left in an inconsistent state.

However, in general, it’s a good idea to use SET XACT_ABORT ON, so that any errors that occur will cause the whole transaction to be rolled back.

2. Don’t ignore errors in stored procedures

When an error occurs in a stored procedure, the default behavior is for execution to stop and an error message to be displayed. However, if the error is ignored, execution will continue as if nothing happened. This can lead to data inconsistencies and incorrect results.

It’s important to remember that not all errors are fatal. Some errors can be handled gracefully without interrupting execution. For example, if a stored procedure tries to insert a record into a table but the record already exists, this could be handled by displaying a warning message instead of stopping execution.

If you’re going to ignore errors, make sure you have a good reason for doing so. Otherwise, you risk introducing bugs and making your code more difficult to maintain.

3. Start transactions explicitly and commit/rollback as necessary

If a stored procedure doesn’t start a transaction, any changes it makes will be automatically committed when the stored procedure completes successfully. This is usually what you want, but there are times when you might not want changes to be committed until the very end, even if the stored procedure succeeds.

For example, suppose you have a stored procedure that inserts rows into two different tables. If the stored procedure doesn’t start a transaction, and an error occurs after the first insert, the second insert will still be committed because the stored procedure didn’t encounter any errors before it completed.

On the other hand, if the stored procedure starts a transaction and an error occurs after the first insert, the second insert will be rolled back because the stored procedure encountered an error before it completed. This is usually what you want, as it ensures that both inserts are either committed or rolled back, and that no data is left in an inconsistent state.

4. Error handling should be centralized

If error handling is not centralized, then it becomes difficult to track down where errors are occurring. This can lead to frustration on the part of developers and DBAs who are trying to debug stored procedures.

Centralized error handling also makes it easier to change the way errors are handled. For example, if you want to add logging to your stored procedure error handling, you can do so in one place instead of having to modify each individual stored procedure.

Finally, centralizing your error handling makes it easier to ensure that all errors are properly handled. If error handling is scattered throughout your stored procedures, it’s easy to forget to add it to a new stored procedure or to make a mistake when modifying existing error handling code.

5. Avoid unnecessary error messages

If you’re handling errors in your stored procedures, then chances are good that you’re also logging those errors. When you log an error, you typically include the message text so that you can later review the logs and determine what went wrong.

The problem is that if you include too much information in your error message, it can clutter up the logs and make them more difficult to review. In addition, it can be helpful to include some context about the error so that you can understand its impact, but including too much information can again make the logs more difficult to review.

Therefore, it’s important to strike a balance when crafting your error messages. Include enough information to be helpful, but don’t include so much that the message becomes cluttered or difficult to understand.

6. Return meaningful error information to the caller

If a stored procedure doesn’t return any error information to the caller, then the caller has no way of knowing that an error occurred. The caller might just think that the stored procedure completed successfully, when in fact it didn’t. This can lead to all sorts of problems, such as data being inserted into the wrong table, or incorrect results being returned.

It’s therefore important to make sure that your stored procedures always return some sort of error information to the caller, even if it’s just a simple “success” or “failure” flag. That way, the caller can at least be aware that an error occurred, and can take appropriate action.

7. Use TRY…CATCH for data access

When an error occurs in a TRY block, control is passed to the associated CATCH block. This allows you to handle errors gracefully and prevent them from propagating up to the calling code. By contrast, if you don’t use TRY…CATCH for data access, any errors that occur will be unhandled and will propagate up to the calling code, potentially causing your application to crash.

TRY…CATCH also allows you to roll back transactions, which is important for maintaining data integrity. In addition, it lets you log information about the error, which can be helpful for troubleshooting purposes.

8. Use nested transactions only if you really need them

If you have a stored procedure that calls another stored procedure, and both procedures have error handling, you may be tempted to use nested transactions. However, this can lead to problems if the inner stored procedure does not roll back properly.

For example, suppose you have a stored procedure that inserts data into a table. The stored procedure has error handling, so if there is an error, it will roll back the transaction. However, suppose the stored procedure calls another stored procedure that also inserts data into a table. If that stored procedure has an error, it will not roll back the transaction. This can lead to data being inserted into the table even though there was an error in the second stored procedure.

To avoid this problem, you should only use nested transactions if you are absolutely sure that the inner stored procedure will always roll back the transaction properly. If you’re not sure, it’s better to use two separate transactions.

9. Keep transaction duration short

Long transactions increase the likelihood of blocking and deadlocks. They also make it more difficult to diagnose problems because it’s harder to identify which statement caused the error when there are many statements in a transaction.

If you do need to run a long transaction, consider using the NOLOCK hint to prevent blocking. This hint should be used with caution, however, as it can lead to dirty reads.

10. Test your error handling code

If you don’t test your error handling code, you won’t know if it works as expected. This can lead to unexpected results when your stored procedure is executed in a production environment.

Testing your error handling code also allows you to verify that the correct error message is displayed to the user. This is important because the error message should be clear and concise so that the user knows what to do next.

Finally, testing your error handling code ensures that your stored procedure will continue to work as expected even if the database or server changes.