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How to delete records in batches while reducing locking

I have used the technique below to delete rows in batches which includes pauses to let other process access the table. USE IT AT YOUR OWN RISK!! I take NO responsibility if you run it on your own system - in fact that goes for any of the code on my blog.


DECLARE @MaxID INT
DECLARE @MinID INT
DECLARE @Date DATETIME
DECLARE @MyTableVar TABLE (ID INT)

SET @Date = GETDATE()

IF EXISTS (SELECT * FROM tempdb..sysobjects WHERE id=OBJECT_ID('tempdb..#DelRows'))
    DROP TABLE #DelRows

CREATE TABLE #DelRows (ID INT)

/*
To try and reduce table scans on large tables we get the minimum and maximum ID (assuming ID is a Clustered Index) of the date range and use those as the minimum and maximum criteria for the filter
*/
-- Find latest ID in range
SET @MaxID = (
              SELECT TOP 1 t1.Table1_ID
              FROM dbo.Table1 t1 WITH (NOLOCK)        
              WHERE t1.TableDate < DATEADD(HOUR, - 24, @date)
              ORDER BY t1.TableDate DESC
              )
-- Find earliest ID in range
SET @MinID = (
              SELECT TOP 1 t1.Table1_ID
              FROM dbo.Table1 t1 WITH (NOLOCK)
              WHERE t1.TableDate >= @Date
              ORDER BY t1.TableDate ASC
              )

-- Insert the records to delete into a temporary table
INSERT #DelRows
SELECT TOP 500000 ID
FROM Table1 t1(NOLOCK)
WHERE t1.Table1_ID BETWEEN @MinID
              AND @MaxID

-- Delete the records in batches of 1000
WHILE 1 = 1
BEGIN
       DELETE TOP (1000) t1
       OUTPUT DELETED.ID
       INTO @MyTableVar
       FROM Table1 t1
       JOIN #DelRows d ON t1.ID = d.ID

       DELETE d2
       FROM #DelRows d2
       JOIN @MyTableVar m ON d2.ID = m.ID

       DELETE @MyTableVar
      
-- We put in a delay to give other queries a chance
       WAITFOR DELAY '000:00:05'

END

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