deadlock on concurrent processes separated by transaction isolation level
We have a workorder table. A server agent jobs grabs 100 entries from this table in a cursor and do some work. To parallelize this there are 10 server agent jobs, which call the following procedure (each with its own @process_id
):
CREATE PROCEDURE sp_do_workorder @process_id INT
AS
BEGIN TRY
DECLARE @wo_id NCHAR(40),
@wo_action NVARCHAR(100),
@created_at DATETIME,
@source_proc_name NVARCHAR(100),
UPDATE procedure_ctrl SET [status]='running' WHERE [procedure]='sp_do_workorder_'+CAST(@process_id AS NVARCHAR(100)) AND [status]='idle'
WHILE 1=1
BEGIN
IF NOT EXISTS (SELECT * FROM procedure_ctrl WHERE [procedure]='sp_do_workorder_'+CAST(@process_id AS NVARCHAR(100)) AND [status]='running') BREAK
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
BEGIN TRANSACTION
UPDATE workorder SET hash=CAST(@process_id AS NVARCHAR(100))
FROM workorder x
INNER JOIN (
SELECT TOP 100 id FROM workorder WHERE hash='' AND workorder_step=0 ORDER BY created_at ASC
) y ON x.id=y.id
COMMIT TRANSACTION
SET TRANSACTION ISOLATION LEVEL READ COMMITTED
DECLARE wo_cur CURSOR FAST_FORWARD FOR SELECT id,action,created_at,optin_source FROM workorder WHERE hash=CAST(@process_id AS NVARCHAR(100)) AND workorder_step=0 ORDER BY created_at ASC
OPEN wo_cur
FETCH NEXT FROM wo_cur INTO @wo_id,@wo_action,@created_at,@source_proc_name
WHILE @@FETCH_STATUS=0
BEGIN
EXEC sp_basisprozess @wo_id,@wo_action,@created_at,@source_proc_name,@process_id
FETCH NEXT FROM wo_cur INTO @wo_id,@wo_action,@created_at,@source_proc_name
END
CLOSE wo_cur
DEALLOCATE wo_cur
WAITFOR DELAY '00:00:01'
END
UPDATE procedure_ctrl SET [status]='idle' WHERE [procedure]='sp_do_workorder_'+CAST(@process_id AS NVARCHAR(100)) AND [status]='running'
END TRY
BEGIN CATCH
EXEC dbo.sp_listerror
DECLARE @error NVARCHAR(4000)
SET @error='[sp_do_workorder]_'+CAST(@process_id AS NVARCHAR(100))+': critical problem'
RAISERROR(@error, 12, 1)
END CATCH
We get a deadlock really often for most of these 10 agent jobs. Has anyone a hint why this is so? To prevent side effects we use serialize transaction isolation level, so only one agent job can grab one workorder entry. Without setting transaction isolation lev开发者_运维知识库en the deadlock are gone, but then it often occurs, that two (or more) agent jobs grab the same workorder entry.
I haven't tried to work out specifically why the deadlock would occur in your case but it seems as though you are effectively using a table as a queue in which case see this linked article for an approach that uses the OUTPUT
clause and locking hints to maximise concurrency without deadlocks.
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