There are 2 different types of deadlocks.Ī cycle deadlock is what happens when a process A which is holding a lock on resource X is waiting to obtain an exclusive lock on resource Y, while at the same time process B is holding a lock on resource Y and is waiting to obtain an exclusive lock on resource X.Ī conversion deadlock occurs when a thread tries to convert a lock from one type to another exclusive type but is unable to do so because another thread is already also holding a shared lock on the same resource. The other user whose process was not selected as the victim will be most likely be completely unaware that their process participated in a deadlock. Transaction (Process ID 62) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. The first sign you will have of a deadlock is the following error message which will be displayed to the user who own the process that was selected as the deadlock victim. SQL Server automatically detects when deadlocks have occurred and takes action by killing one of the processes known as the victim.ĭeadlocks do not only occur on locks, from SQL Server 2012 onward, deadlocks can also happen with memory, MARS (Multiple Active Result Sets) resources, worker threads and resources related to parallel query execution. The only way out of a deadlock is for one of the processes to be terminated. This results in a standoff where neither process can proceed. In this series, I will provide all of the information you need to understand in order to deal with deadlocks.Ī deadlock occurs when 2 processes are competing for exclusive access to a resource but is unable to obtain exclusive access to it because the other process is preventing it.
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