deadloack on Azure SQL Database table

Question

Hi Team,

I have an Azure SQL Database table which at once is accessed by many processes(written in different language/framework) to perform update statements on the table, due to which a deadlock is happening. Error statement is as below -

Error executing sql statement: Transaction (Process ID some number) was deadlocked on lock | communication buffer resources with another process and has been chosen as the deadlock victim. Rerun the transaction.

Can you please let me know the solution for above issue so that deadlock could be avoided.

Please let me know if more information is needed on above issue.

Thanks,

Salil

Answer 1

Deadlock solutions in SQL can be complex to work through.

I'd suggest reviewing the guidance in this document https://learn.microsoft.com/en-us/azure/azure-sql/database/analyze-prevent-deadlocks?view=azuresql&tabs=ring-buffer and formulating an approach for your scenario.

In particular there is a section that provides suggestions for increasing blocking; https://learn.microsoft.com/en-us/azure/azure-sql/database/analyze-prevent-deadlocks?view=azuresql&tabs=ring-buffer#look-for-patterns-that-increase-blocking. Of these suggestions, I've previously found that a mature table-hint approach has really helped deadlocking in my apps.

Answer 2

Hi @salilsingh-9961

I understand that you are facing a deadlock issue on your Azure SQL Database table, which is being accessed by multiple processes simultaneously.

As you may be aware, a deadlock occurs when two or more transactions are waiting for each other to release locks, resulting in a circular dependency. In your case, it seems that multiple processes are trying to update the same table simultaneously, causing a deadlock.

To resolve this issue, you can try the following steps:

1. Identify the queries that are causing the deadlock. You can use the SQL Server Profiler or Extended Events to capture the deadlock graph. The deadlock graph will provide you with information about the queries involved in the deadlock and the resources they are waiting for.

Please find detailed blog on “How to obtain the deadlocks of your Azure SQL Database or Managed Instance?

https://techcommunity.microsoft.com/t5/azure-database-support-blog/lesson-learned-19-how-to-obtain-the-deadlocks-of-your-azure-sql/ba-p/368847

2. Once you have identified the queries causing the deadlock, you can optimize them to reduce the chances of a deadlock occurring. You can try to reduce the transaction size, use appropriate isolation levels, and avoid long-running transactions.
3. Optimize your database indexes: Make sure that your database indexes are properly optimized and that you're not running any unnecessary queries. Improperly indexed tables can lead to more locks and deadlocks. 
4. Reduce lock contention: If you are using a database that supports row-level locking, make sure you're using it. Use the smallest possible lock granularity to reduce lock contention. 
5. Handle deadlocks properly: Your application should be able to handle deadlocks by detecting them and re-trying the transaction that caused the deadlock. Using a library like Dapper or Entity Framework will help you to handle deadlocks automatically for you. 
6. Split the transactions: if your transactions are too big, you can consider splitting them into smaller transactions.
7. Review the code: check the code in the parts where the error occurred, the problem may be a logic problem in your code that you need to fix.

I hope this helps.

Thank you!