Improve Performance -Update query with OR in WHERE

Question

Improve Performance -Update query with OR in WHERE

bharat sethi

SSCommitted

Points: 1831
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December 18, 2013 at 5:40 am

#301479

Hi! How do we improve this Update query Performance as currently it is taking 1 Minute to update 17643 Rows.
Query ->
Declare @date datetime = '09-Dec-2013'
update #tmp_sp_abc
set test = rtrim(xyz_test)
from #tmp_sp_abc t1,
t_h_bg_pc_it t2
where (t2.id_i = t1.i or t2.id_s1 = t1.s)
and t1.r_type = 1
and t2.[date] = @date
Tables Row Count: -
#tmp_sp_abc -> 125352
t_h_bg_pc_it -> 14798 Rows
t_h_bg_pc_it table has 300 columns with primary key on id_i column
and
#tmp_sp_abc has 11 columns with no primary key and no indexes.
found that "OR" condition is the root cause of this much time consumption but, can't change it.
tried to add indexes on: -
Table: - t_h_bg_pc_it
Columns: - [xyz_test], [id_i], [id_s1], [date]
Table: - #tmp_sp_abc
Columns: - , , [r_type] include [test]
but, by doing this saved only 5 seconds.
Attaching the Execution Plan Snaps (Without above indexes and with indexes).
Please advice.

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Gail Shaw SSC Guru Points: 1004504 More actions · Answer 1

Could you post the execution plans please, not pictures of the plans?

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Lowell SSC Guru Points: 323518 More actions · Answer 2

what if you change the Or to be two distinct update statemetns instead?

DECLARE @date DATETIME = '09-Dec-2013'

--part1

UPDATE #tmp_sp_abc

SET test = RTRIM(xyz_test)

FROM

#tmp_sp_abc t1,

t_h_bg_pc_it t2

WHERE t2.id_i = t1.i

AND t1.r_type = 1

AND t2.[date] = @date

--part2

UPDATE #tmp_sp_abc

SET test = RTRIM(xyz_test)

FROM

#tmp_sp_abc t1,

t_h_bg_pc_it t2

WHERE t2.id_s1 = t1.s

AND t1.r_type = 1

AND t2.[date] = @date

Lowell

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bharat sethi SSCommitted Points: 1831 More actions · Answer 3

Hi!

First of all can't separate the OR. and tried this but, getting diff. in output of 5417 rows (may be due to some rows have values in both columns. That can be manageable).

But, biz. guys are not allowing to user 2 UPDATE statements.

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 4

bharat sethi (12/18/2013)
Hi!
First of all can't separate the OR. and tried this but, getting diff. in output of 5417 rows (may be due to some rows have values in both columns. That can be manageable).
But, biz. guys are not allowing to user 2 UPDATE statements.

Sometimes the performance of this type of join can be improved by left joining the table twice and filtering for a match in at least one of them, like this:

UPDATE t1 SET

test = RTRIM(ISNULL(t2.xyz_test,t3.xyz_test))

FROM #tmp_sp_abc t1

LEFT JOIN t_h_bg_pc_it t2

ON t2.id_i = t1.i

AND t2.[date] = @date

LEFT JOIN t_h_bg_pc_it t3

ON t3.id_s1 = t1.s

AND t3.[date] = @date

WHERE t1.r_type = 1

AND (t2.id_i IS NOT NULL OR t3.id_s1 IS NOT NULL)

However, without an execution plan to work with, it's a stab in the dark. I'd try creating a clustered index on t1.i and an ordinary index on t1.s. Also, always run the query as a SELECT first and check the execution plan:

SELECT

test,

RTRIM(ISNULL(t2.xyz_test,t3.xyz_test))

FROM #tmp_sp_abc t1

LEFT JOIN t_h_bg_pc_it t2

ON t2.id_i = t1.i

AND t2.[date] = @date

LEFT JOIN t_h_bg_pc_it t3

ON t3.id_s1 = t1.s

AND t3.[date] = @date

WHERE t1.r_type = 1

AND (t2.id_i IS NOT NULL OR t3.id_s1 IS NOT NULL)

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

bharat sethi SSCommitted Points: 1831 More actions · Answer 5

bharat sethi

SSCommitted

Points: 1831

December 18, 2013 at 7:10 am

#1674416

PFA the ExecutionPlan and please advice.

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 6

Here's an alternative query form which reduces the row count from the permanent table:

UPDATE t1 SET

test = RTRIM(x.xyz_test)

FROM #tmp_sp_abc t1

CROSS APPLY (

SELECT TOP 1 xyz_test

FROM t_h_bg_pc_it t2

WHERE (t2.id_i = t1.i OR t2.id_s1 = t1.s)

AND t2.[date] = @date

-- choose a sensible ORDER BY

) x

WHERE t1.r_type = 1

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

bharat sethi SSCommitted Points: 1831 More actions · Answer 7

Hi!

Please assist that "Order By" clause is necessary in this query and is there any wrong outcome if we do not use this Order by clause? Please share the info. on this and advise do we need to use the Columns in Order By which we have in WHERE clause? Need to know so that will take care of this.

darshan SSC Journeyman Points: 87 More actions · Answer 8

Hi,

Create another index as below:

Table: - #tmp_sp_abc

Columns: - , , [r_type] include [test]

Also, you can create an indexed view on [t_h_bg_pc_it] with only required columns. You need to consider how often [t_h_bg_pc_it] is being updated as Indexed view may slow down updates.

Index on [t_h_bg_pc_it] table, should start with columns that you use in Where clause and include columns that you use in Set clause.

Kindest Regards,

darshan Joshi

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 9

bharat sethi (12/18/2013)
Hi!
Please assist that "Order By" clause is necessary in this query and is there any wrong outcome if we do not use this Order by clause? Please share the info. on this and advise do we need to use the Columns in Order By which we have in WHERE clause? Need to know so that will take care of this.

The CROSS APPLY block resolves the case where the temp table has multiple matches in t_h_bg_pc_it using your chosen predicates. If there are no multiple matches then you don't need TOP or ORDER BY. If there are multiple matches then you should examine them. If the values of xyz_test are identical for each row then retain TOP but you don't strictly need ORDER BY (I'd use it in any case - match the ordering of the index/cluster you're reading from to avoid an unnecessary sort). If the values of xyz_test are not identical for each row then ORDER BY offers you an opportunity to choose between them.

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden