Question

I’m getting alot of deadlocks on a table.
It is SQL Server 2005

the sp that is getting the error does the following

Delete From
    EmployeeAccrualAdj 
Where
    EmployeeID = @iEmployeeID and 
    SchemeCode = @sSchemeCode and
    AdjTypeCode = @sAdjTypeCode and
    EffectiveDate >= @dtDateFrom

I’m trying to work out if the database is doing row, page or table locking when deleting?

Also, I am thinking of re-writing the sp to

declare @ToDelete table (id int IDENTITY(1,1),
                         AccrualAdjID int NOT NULL)


insert into @ToDelete
SELECT 
    AccrualAdjID
FROM 
    EmployeeAccrualAdj
Where
    EmployeeID = @iEmployeeID and 
    SchemeCode = @sSchemeCode and
    AdjTypeCode = @sAdjTypeCode and
    EffectiveDate >= @dtDateFrom


DECLARE @iCount int, @iMax int
SELECT 
    @iCount = 1, @iMax = MAX(id)
FROM 
    @ToDelete

declare @iAccrualAdjID int

WHILE @iCount <= @iMax
BEGIN

    select @iAccrualAdjID = AccrualAdjID FROM @ToDelete WHERE id = @iCount

    DELETE FROM EmployeeAccrualAdj
    WHERE @iAccrualAdjID = AccrualAdjID


    SET @iCOunt = @iCount + 1
END

Effectivly looping through the rows to be deleted and deleting them one at a time.

I’m thinking this will not make any difference if there is row locking , but will if there is page or table locking
What do you all reckon??

Answer 1

The answer depends on the lock escalation rules. The cursor-based approach you are wondering about will be amazingly slow if you have very many rows. I’d look into what other queries are hitting that table during the DELETE operation and see whether you can block them for the duration of the delete with a preemptive lock acquisition.

This article gives an example of how to acquire the needed locks up front with an UPDLOCK locking hint.