SQL DB script performance tuning - sql

Question

I need to fix a prod DB issue and the clean up script I've is taking really long. I tried couple of things without any luck, following is the script:
DECLARE #ErrorMessage NVARCHAR(4000)
DECLARE #ErrorSeverity INT
DECLARE #ErrorState INT
DECLARE #ErrorProcedure NVARCHAR(50)
BEGIN TRY
IF OBJECT_ID('tempdb..#SuspectData') IS NOT NULL
BEGIN
DROP TABLE #SuspectData
END
CREATE TABLE #SuspectData
(
IID INT,
CID INT,
PID INT
)
INSERT INTO dbo.#SuspectData
SELECT DL.IID,DL.CID,IT.PID FROM DL
INNER JOIN IT ON IT.CID = DL.CID AND IT.IID = DL.IID
WHERE DL.Suspect = 1
WHILE (1 = 1)
BEGIN
BEGIN TRANSACTION
UPDATE TOP (5000) TDS
SET TDS.DTID = 4
FROM
TDS
INNER JOIN dbo.#SuspectData SD
ON TDS.IID = SD.IID AND TDS.PID = SD.PID
WHERE TDS.DTID <> 4
IF ##ROWCOUNT = 0
BEGIN
COMMIT TRANSACTION
BREAK
END
COMMIT TRANSACTION
END
WHILE (1 = 1)
BEGIN
BEGIN TRANSACTION
UPDATE TOP (5000) TDA
SET TDA.DTID = 4
FROM
TDA
INNER JOIN dbo.#SuspectData SD
ON TDA.IID = SD.IID AND TDA.PID = SD.PID
WHERE TDA.DTID <> 4
IF ##ROWCOUNT = 0
BEGIN
COMMIT TRANSACTION
BREAK
END
COMMIT TRANSACTION
END
DROP TABLE #SuspectData
END TRY
BEGIN CATCH
SELECT #ErrorMessage = ERROR_MESSAGE(),
#ErrorSeverity = ERROR_SEVERITY(),
#ErrorState = ERROR_STATE(),
#ErrorProcedure = ERROR_PROCEDURE()
RAISERROR (#ErrorMessage,#ErrorSeverity,#ErrorState,#ErrorProcedure) ;
END CATCH
I also have following script to update everything at same time but it is also taking really long time like 24 hours or something.
DECLARE #ErrorMessage NVARCHAR(4000)
DECLARE #ErrorSeverity INT
DECLARE #ErrorState INT
DECLARE #ErrorProcedure NVARCHAR(50)
BEGIN TRY
IF OBJECT_ID('tempdb..#SuspectData') IS NOT NULL
BEGIN
DROP TABLE #SuspectData
END
CREATE TABLE #SuspectData
(
IID INT,
CID INT,
PID INT
)
INSERT INTO dbo.#SuspectData
SELECT DL.IID,DL.CID,IT.PID FROM DL
INNER JOIN IT ON IT.CID = DL.CID AND IT.IID = DL.IID
WHERE DL.Suspect = 1
BEGIN TRANSACTION
--Update about 1.5M records
UPDATE TDS
SET TDS.DTID = 4
FROM
TDS
INNER JOIN dbo.#SuspectData SD
ON TDS.IID = SD.IID AND TDS.PID = SD.PID
WHERE TDS.DTID <> 4
COMMIT TRANSACTION
BEGIN TRANSACTION
--Update about 4.5M records
UPDATE TDA
SET TDA.DTID = 4
FROM
TDA
INNER JOIN dbo.#SuspectData SD
ON TDA.IID = SD.IID AND TDA.PID = SD.PID
WHERE TDA.DTID <> 4
COMMIT TRANSACTION
DROP TABLE #SuspectData
END TRY
BEGIN CATCH
SELECT #ErrorMessage = ERROR_MESSAGE(),
#ErrorSeverity = ERROR_SEVERITY(),
#ErrorState = ERROR_STATE(),
#ErrorProcedure = ERROR_PROCEDURE()
RAISERROR (#ErrorMessage,#ErrorSeverity,#ErrorState,#ErrorProcedure) ;
END CATCH

Answer 1

I'm guessing that TDS table is large. In that case you can speed up join operation between your temp table and TDS (ON TDS.IID = SD.IID AND TDS.PID = SD.PID) by creating index on your temporary table:
either primary clustered:
CREATE TABLE #SuspectData
(
IID INT,
CID INT,
PID INT,
CONSTRAINT pk_temp PRIMARY KEY(IID, PID)
)
or not-clustered (if IID-PID pairs are not unique):
CREATE INDEX IDX_Temp_SuspectData ON #SuspectData(IID,PID)
What you can also do is check execution plan of those queries - it will help you locate which operation takes so long.
On the side: I'm generally against using cursors if you can avoid it.

Answer 2

First, is there anything that changes DL.Suspect = 1 to something else? or does your data set just keep getting bigger?
I also agree with Sean Lange, does the update have to be all or nothing?
I would recommend using a cursor. cursors are a great way to break up large transaction to speed up use and reduce table locks.
DECLARE db_cursor CURSOR FOR SELECT DL.IID,DL.CID,IT.PID FROM DL
INNER JOIN IT ON IT.CID = DL.CID AND IT.IID = DL.IID
WHERE DL.Suspect = 1;
DECLARE #first INT;
DECLARE #second INT;
DECLARE #third INT;
OPEN db_cursor;
FETCH NEXT FROM db_cursor INTO #first , #second , #third ;
WHILE ##FETCH_STATUS = 0
BEGIN
-- Do your updates one row at a time here
UPDATE TDS
SET TDS.DTID = 4
FROM TDS
WHERE TDS.IID = #first AND TDS.PID = #third
WHERE TDS.DTID <> 4
END;
CLOSE db_cursor;
DEALLOCATE db_cursor;