T-SQL – Avoid deadlock and workaround in SQL Server

>Here are some tips on how to avoid deadlocking on your SQL Server:

  • Ensure the database design is properly normalized.
  • Have the application access server objects in the same order each time.
  • During transactions, don’t allow any user input. Collect it before the transaction begins.
  • Avoid cursors.
  • Keep transactions as short as possible. One way to help accomplish this is to reduce the number of round trips between your application and SQL Server by using stored procedures or keeping transactions with a single batch. Another way of reducing the time a transaction takes to complete is to make sure you are not performing the same reads over and over again. If you do need to read the same data more than once, cache it by storing it in a variable or an array, and then re-reading it from there.
  • Reduce lock time. Try to develop your application so that it grabs locks at the latest possible time, and then releases them at the very earliest time.
  • If appropriate, reduce lock escalation by using the ROWLOCK or PAGLOCK.
  • Consider using the NOLOCK hint to prevent locking if the data being locked is not modified often.
  • If appropriate, use as low of an isolation level as possible for the user connection running the transaction.
  • Consider using bound connections.

However, deadlock still occurs sometimes.So we have to deal with it by re-submit the transaction again. See below sample:

Declare @Count int = 0
Declare @MaxErrorAllow int = 3
While @Count < @MaxErrorAllow
Begin
      Begin try
            Update TableTest Set NAME = ‘test’ where ID = 5
            break
      End try
      Begin Catch
            Set @Count = @Count + 1      
            print ERROR_MESSAGE() + convert(varchar(100),GetDate())
            waitfor delay ’00:00:05′ — Delay 5 second before UPDATE again
      End Catch
End
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