The output from this trace flag can be a bit complex to follow at first if you are not used to reading the information contained within it. The first way to get a deadlock graph is to enable trace flag 1222 which is a newer version of trace flag 1204 which existed in SQL Server 2000 to output deadlock graph information. In SQL Server 2005, there are two different ways to get the deadlock graph. To properly resolve deadlocks in SQL Server the first that you will need is the deadlock graph. This however, is not actually solving the deadlock, it is just preventing the deadlock from being problematic and causing data/productivity losses to occur. Generally speaking, the locking scenario that existed to cause the deadlock will not exist during the resubmission and the transaction will complete successfully the second time around. A properly designed and coded application will have exception handling built around all connections to SQL Server that can intercept the 1205 error and resubmit the deadlock victim request back to SQL Server. The first thing to consider when troubleshooting deadlocks is that a deadlock in and of itself is not necessarily a problem. Once this has been determined, that process is killed and a 1205 error is returned to the client. When the deadlock monitor in SQL Server encounters a deadlock, it immediately analyzes the processes contributing to the deadlock and determines which will be the least expensive to rollback. What most people don't realize is that while there are many different types of deadlocks, the methods used to resolve them all is fundamentally the same. It's fairly common knowledge that deadlocks in SQL Server are caused by a cyclic dependency between multiple processes, threads or sessions, for a set of resources in SQL Server.
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