Stored procedure slowed all of a sudden - sql

Question

I have a procedure which is basically inserting records to a table from selection of few table and views combinations
and SQL is like below
ALTER PROCEDURE [dbo].[aka_spring_rep_sum]
AS
INSERT INTO tbl_spring (col1,col2,....colx)
SELECT col1,col2...colx
FROM vw_tbl_spring bk
LEFT JOIN
(SELECT col1,col2,..
FROM vw_tbl_prices_spring) sp ON bk.col1 = sp.col1
AND bk.col2 = sp.col2
LEFT JOIN
(SELECT col1,col2...
FROM tbl_xx) stock ON bk.col1 = stock.col1
AND bk.col2 = stock.col2
LEFT JOIN
(SELECT DISTINCT col1,col2,....
FROM tbl_v) sf ON bk.col1 = sf.col1
AND bk.colx = sf.colx
LEFT JOIN
(SELECT DISTINCT col1, col2
FROM tbl_bb) vr ON sf.col1 = vr.col1
LEFT JOIN
(SELECT col1, is
FROM tbl_ss) sh ON bk.col1 = sh.col1
OPTION (RECOMPILE)
The stored procedure was taking less than 2-3 seconds only till today, but today all of a sudden this was taking very long time 30 minutes plus and never ending and forced to stop manually.
After breaking the different selections one by one I found that
select ..... FROM vw_tbl_spring bk
is ended up as a never ending call. Rest all select statements in the stored procedure are returning results less than 1 seconds.
ALTER VIEW [dbo].[vw_tbl_spring]
AS
SELECT col1, col2...., colx
FROM
(SELECT Icol1, col2, ....
FROM
(
SELECT DISTINCT col1,col2,... FROM tbl_pens s
INNER JOIN tbl_penh h ON s.col1 = h.col1 AND s.col2 = h.col2
WHERE s.col6 >= 21 AND h.col1 = 'X'
)
) b
LEFT JOIN
( SELECT col1,col2,...... FROM tbl_pens s
INNER JOIN tbl_penh h ON ON s.col1 = h.col1 AND s.col2 = h.col2
WHERE WHERE s.col6 >= 21 AND h.col1 = 'X'
) p ON b.col1 = p.col1 AND b.col1 = p.col1
LEFT JOIN vw_tbl_kk k ON p.col1 = k.col1 AND p.col1 = k.col2
Again filtering the different selections inside this view found out that the last left join is slowing things down
If we removed the last left join ie
LEFT JOIN vw_tbl_kk k ON p.col1 = k.col1 AND p.col1 = k.col2
Everything will be as normal ie will return results in less than 2-3 seconds
Unable to find what is the reason behind this sudden slowness
The same behaviour occurred a few months back and that time try to delete and recreate all associated views and stored procedure and then the issue was resolved. But this time this also didn't help
Any way to check what is causing this slowness in SQL Server?

Answer 1

Your query is a 6-way join. This means that if there are n rows that join in each joined table, there will be n6 resulting rows to insert. To highlight the exponential growth this causes:
rows in each table that join | number of resultant rows
1 | 1
2 | 64
3 | 729
4 | 4,096
10 | 1,000,000
There are probably suddenly more joining rows in the tables, not only making it slower, but also hitting the logging high water mark, which means the database must rollback the transaction, which is typically very slow.