delete in small chunks from cursor data - T-SQL stored Procedure - sql-server

Question

i have written this t-sql stored procedure.
This is working fine , but since this stored procedure will be used to delete a lot of data (for example 1M to 2M) , I think, this can cause some locks in the table, or cause some db performance etc. So I am thinking, if we delete in batch for example at a time delete 1000 records. I am not totally sure about how to do this without cause any issue in db.
ALTER PROCEDURE [schema].[purge_data] #count INT---(count input can be in millions)
AS
DECLARE #p_number VARCHAR(22)
,#p_r_number VARCHAR(5)
DECLARE data_cursor CURSOR
FOR
SELECT TOP (#count) JRC_policy_number
,jrc_part_range_nbr
FROM [staging].[test].[p_location]
WHERE JRC_POLICY_TERM_DT < CAST('19950101 00:00:00.000' AS DATETIME)
AND jrc_policy_status = 'T'
OPEN data_cursor
FETCH NEXT
FROM data_cursor
INTO #p_number
,#p_r_number
WHILE ##FETCH_STATUS = 0
BEGIN
DELETE
FROM [staging].[test].[p_location]
WHERE JRC_policy_number = #p_number
AND jrc_part_range_nbr = #p_r_number
FETCH NEXT
FROM data_cursor
INTO #p_number
,#p_r_number
END
CLOSE data_cursor
DEALLOCATE data_cursor
Edit :
I had already tried without cursor - direct delete query like below.
DELETE TOP (1000) FROM [MyTab] WHERE YourConditions
It was very fast , it took 34 seconds to delete 1M records, but , during the 34 seconds, the table was locked completely. In production p_locator table is being used 24/7 , and being used by a very critical application, which expects response time in milliseconds, our purge script should not impact the the main application in any way. that's why I have chosen this cursor approach. pls guide

Answer 1

With some of your references I've written the below stored proc. Ofcourse there will be ALOT of scope for improvements. Pls share.
ALTER PROCEDURE [dbo].[purge_data] #count INT
AS
DECLARE #iteration INT
,#remainder INT
,#current_count INT
BEGIN
SELECT #current_count = count(*)
FROM PROD_TBL
WHERE JRC_POLICY_TERM_DT < CAST('19950101 00:00:00.000' AS DATETIME)
AND JRC_POLICY_STATUS = 'T'
AND JRC_PLCY_ADMIN_SYS_CD = 'X'
IF (#current_count < #count)
BEGIN
SET #count = #current_count
END
SET #iteration = #count / 10000
SET #remainder = #count % 10000
WHILE (#iteration > 0)
BEGIN
DELETE
FROM PROD_TBL
FROM (
SELECT TOP 10000 JRC_POLICY_NUMBER
,JRC_PART_RANGE_NBR
,JRC_PLCY_ADMIN_SYS_CD
FROM PROD_TBL
WHERE JRC_POLICY_TERM_DT < CAST('19950101 00:00:00.000' AS DATETIME)
AND JRC_POLICY_STATUS = 'T'
AND JRC_PLCY_ADMIN_SYS_CD = 'X'
) pol_locator_tbl
WHERE PROD_TBL.JRC_POLICY_NUMBER = pol_locator_tbl.JRC_POLICY_NUMBER
AND PROD_TBL.JRC_PART_RANGE_NBR = pol_locator_tbl.JRC_PART_RANGE_NBR
AND PROD_TBL.JRC_PLCY_ADMIN_SYS_CD=pol_locator_tbl.JRC_PLCY_ADMIN_SYS_CD
SET #iteration = #iteration - 1
END
IF (#remainder > 0)
BEGIN
DELETE
FROM PROD_TBL
FROM (
SELECT TOP (#remainder) JRC_POLICY_NUMBER
,JRC_PART_RANGE_NBR
,JRC_PLCY_ADMIN_SYS_CD
FROM PROD_TBL
WHERE JRC_POLICY_TERM_DT < CAST('19950101 00:00:00.000' AS DATETIME)
AND JRC_POLICY_STATUS = 'T'
AND JRC_PLCY_ADMIN_SYS_CD = 'X'
) pol_locator_tbl
WHERE PROD_TBL.JRC_POLICY_NUMBER = pol_locator_tbl.JRC_POLICY_NUMBER
AND PROD_TBL.JRC_PART_RANGE_NBR = pol_locator_tbl.JRC_PART_RANGE_NBR
AND PROD_TBL.JRC_PLCY_ADMIN_SYS_CD=pol_locator_tbl.JRC_PLCY_ADMIN_SYS_CD
END
END
END