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Our client side code detects deadlocks, waits for an interval, then retries the request up to 5 times. The retry logic detects the deadlocks based on the error number 1205.
My goal is to test both the deadlock retry logic and deadlock handling inside of various stored procedures. I can create a deadlock using two different connections. However, I would like to simulate a deadlock inside of a single stored procedure itself.
A deadlock raises the following error message:
Msg 1205, Level 13, State 51, Line 1
Transaction (Process ID 66) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.
I see this error message is in sys.messages:
select * from sys.messages where message_id = 1205 and language_id = 1033 message_id language_id severity is_event_logged text 1205 1033 13 0 Transaction (Process ID %d) was deadlocked on %.*ls resources with another process and has been chosen as the deadlock victim. Rerun the transaction. I can't raise this error using RAISERROR:
raiserror(1205, 13, 51) Msg 2732, Level 16, State 1, Line 1
Error number 1205 is invalid. The number must be from 13000 through 2147483647 and it cannot be 50000.
Our deadlock retry logic checks if the error number is 1205. The deadlock needs to have the same message ID, level, and state as a normal deadlock.
Is there a way to simulate a deadlock (with RAISERROR or any other means) and get the same message number out with just one process?
Our databases are using SQL 2005 compatibility, though our servers vary from 2005 through 2008 R2.
623
The process of creating a deadlock is simple. First execute the first update statement from the first transaction and then execute the first update statement from the second transaction. This will create locks on table1 and table2. Now execute the second update statement from transaction1.
In terms of SQL Server, a deadlock occurs when two (or more) processes lock the separate resource. Under these circumstances, each process cannot continue and begins to wait for others to release the resource.
Even on a table with only one index, deadlock can occur if it has more than 1 row, because we again have at least 2 hashes to lock and now all depends on order we lock them. Since almost every databases has more than 1 row in total, deadlock can occur in any database.
As many have pointed out, the answer is no, a single process cannot reliably deadlock itself. I came up with the following solution to simulate a deadlock on a development or test system..
Run the script below in a SQL Server Management Studio window. (Tested on 2008 R2 only.) You can leave it running as long as necessary.
In the place you want to simulate a deadlock, insert a call to sp_simulatedeadlock. Run your process, and the deadlock should occur.
When done testing, stop the SSMS query and run the cleanup code at the bottom.
/* This script helps simulate deadlocks. Run the entire script in a SQL query window. It will continue running until stopped. In the target script, insert a call to sp_simulatedeadlock where you want the deadlock to occur. This stored procedure, also created below, causes the deadlock. When you are done, stop the execution of this window and run the code in the cleanup section at the bottom. */ set nocount on if object_id('DeadlockTest') is not null drop table DeadlockTest create table DeadlockTest ( Deadlock_Key int primary key clustered, Deadlock_Count int ) go if exists (select * from sysobjects where id = object_id(N'sp_simulatedeadlock') AND objectproperty(id, N'IsProcedure') = 1) drop procedure sp_simulatedeadlock GO create procedure sp_simulatedeadlock ( @MaxDeadlocks int = -1 -- specify the number of deadlocks you want; -1 = constant deadlocking ) as begin set nocount on if object_id('DeadlockTest') is null return -- Volunteer to be a deadlock victim. set deadlock_priority low declare @DeadlockCount int select @DeadlockCount = Deadlock_Count -- this starts at 0 from DeadlockTest where Deadlock_Key = 2 -- Trace the start of each deadlock event. -- To listen to the trace event, setup a SQL Server Profiler trace with event class "UserConfigurable:0". -- Note that the user running this proc must have ALTER TRACE permission. -- Also note that there are only 128 characters allowed in the trace text. declare @trace nvarchar(128) if @MaxDeadlocks > 0 AND @DeadlockCount > @MaxDeadlocks begin set @trace = N'Deadlock Test @MaxDeadlocks: ' + cast(@MaxDeadlocks as nvarchar) + N' @DeadlockCount: ' + cast(@DeadlockCount as nvarchar) + N' Resetting deadlock count. Will not cause deadlock.' exec sp_trace_generateevent @eventid = 82, -- 82 = UserConfigurable:0 through 91 = UserConfigurable:9 @userinfo = @trace -- Reset the number of deadlocks. -- Hopefully if there is an outer transaction, it will complete and persist this change. update DeadlockTest set Deadlock_Count = 0 where Deadlock_Key = 2 return end set @trace = N'Deadlock Test @MaxDeadlocks: ' + cast(@MaxDeadlocks as nvarchar) + N' @DeadlockCount: ' + cast(@DeadlockCount as nvarchar) + N' Simulating deadlock.' exec sp_trace_generateevent @eventid = 82, -- 82 = UserConfigurable:0 through 91 = UserConfigurable:9 @userinfo = @trace declare @StartedTransaction bit set @StartedTransaction = 0 if @@trancount = 0 begin set @StartedTransaction = 1 begin transaction end -- lock 2nd record update DeadlockTest set Deadlock_Count = Deadlock_Count from DeadlockTest where Deadlock_Key = 2 -- lock 1st record to cause deadlock update DeadlockTest set Deadlock_Count = Deadlock_Count from DeadlockTest where Deadlock_Key = 1 if @StartedTransaction = 1 rollback end go insert into DeadlockTest(Deadlock_Key, Deadlock_Count) select 1, 0 union select 2, 0 -- Force other processes to be the deadlock victim. set deadlock_priority high begin transaction while 1 = 1 begin begin try begin transaction -- lock 1st record update DeadlockTest set Deadlock_Count = Deadlock_Count from DeadlockTest where Deadlock_Key = 1 waitfor delay '00:00:10' -- lock 2nd record (which will be locked when the target proc calls sp_simulatedeadlock) update DeadlockTest set Deadlock_Count = Deadlock_Count from DeadlockTest where Deadlock_Key = 2 rollback end try begin catch print 'Error ' + convert(varchar(20), ERROR_NUMBER()) + ': ' + ERROR_MESSAGE() goto cleanup end catch end cleanup: if @@trancount > 0 rollback drop procedure sp_simulatedeadlock drop table DeadlockTest If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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