Re: Why the monstrous SORT?
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 7 Jul 2005 08:50:49 +0100
I've cut out the critical bit of the execution plan:
4768 NESTED LOOPS (OUTER)
4769 NESTED LOOPS (OUTER)
...
4334 VIEW
1127322080 SORT (GROUP BY)
237018 NESTED LOOPS ****
2 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'OE_CONTROL'
237018 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'AR_DOC_LINE'
You have a nested loop outer join into a view - Oracle has had
to instantiate the view because of the outer join. (8i has to do
this, 9i can sometimes merge the view in these circumstances,
both may be able to push join predicates).
The statistics are misleading - Oracle has to instantiate the
view 4,769 times because of the nested loop - and each
instantiation performs a join returning 237,018 rows
(line marked **** above), and those rows have to be
sorted for each instantiation.
1127322080 / 237018 = 4,756
Oracle doesn't always report the right numbers in the
right places. From time to time you get numbers reported
which are input counts rather than output counts, sometimes
you get numbers which are 'per execution' counts rather
than 'for all executions'
Regards
Jonathan Lewis
Now waiting on the publishers: Cost Based Oracle - Volume 1
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/appearances.html
Public Appearances - schedule updated June 22nd 2005
----- Original Message -----
From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Thursday, July 07, 2005 12:29 AM
Subject: Why the monstrous SORT?
Hi,
I've got an application query that is taking hours to run. After tracing
and running tkprof, I see the execution plan below. Yes, it's a monster of
a query, but Oracle seems to handle it pretty well except for the huge
amount of rows being returned by the SORT (GROUP BY) step. How can it
possibly have to sort so many rows (1.1 Billion!), when it is only getting
237,018 rows from the previous NESTED LOOP step? Any idea how to prevent or
minimize this sort?
Thanks!
Brandon
Rows Execution Plan
------- ---------------------------------------------------
0 SELECT STATEMENT GOAL: CHOOSE
11 MINUS
14 SORT (UNIQUE)
14 FILTER
285 SORT (GROUP BY)
4768 NESTED LOOPS (OUTER)
4769 NESTED LOOPS (OUTER)
4769 NESTED LOOPS
4769 NESTED LOOPS
285 HASH JOIN
197 VIEW OF 'AR_SALESPERSON_CODE'
197 SORT (UNIQUE)
197 SORT (GROUP BY)
197 HASH JOIN
212 TABLE ACCESS GOAL: ANALYZED (FULL) OF
'CT_TEAM_MEMBER'
5637 TABLE ACCESS GOAL: ANALYZED (FULL) OF
'CT_ADD_NAMES'
284 NESTED LOOPS
2 MERGE JOIN (CARTESIAN)
2 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'AR_CUSTOMER_MASTER'
2 INDEX GOAL: ANALYZED (RANGE SCAN) OF
'AR_CUSTOMER_MASTER_PK' (UNIQUE)
2 SORT (JOIN)
1 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'OE_CONTROL'
284 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'OE_HDR'
285 INDEX GOAL: ANALYZED (RANGE SCAN) OF 'OE_HDR_2'
(NON-UNIQUE)
5052 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'OE_LINE'
5052 INDEX GOAL: ANALYZED (RANGE SCAN) OF 'OE_LINE_PK'
(UNIQUE)
9536 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'OE_SUB_ENTITY'
9536 INDEX GOAL: ANALYZED (UNIQUE SCAN) OF
'HM_OE_SUB_ENTITY_UK1' (UNIQUE)
4768 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'HM_INVOICE_SUB_ENTITY_CONTROL'
9536 INDEX GOAL: ANALYZED (UNIQUE SCAN) OF
'HM_INVOICE_SE_CONTROL_PK' (UNIQUE)
4334 VIEW
1127322080 SORT (GROUP BY)
237018 NESTED LOOPS
2 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'OE_CONTROL'
237018 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'AR_DOC_LINE'
3 SORT (UNIQUE)
3 FILTER
4 SORT (GROUP BY)
8 NESTED LOOPS (OUTER)
9 NESTED LOOPS (OUTER)
9 NESTED LOOPS
9 NESTED LOOPS
4 HASH JOIN
3 NESTED LOOPS
2 MERGE JOIN (CARTESIAN)
2 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'AR_CUSTOMER_MASTER'
2 INDEX GOAL: ANALYZED (RANGE SCAN) OF
'AR_CUSTOMER_MASTER_PK' (UNIQUE)
2 SORT (JOIN)
1 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'OE_CONTROL'
3 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'OE_HDR'
285 INDEX GOAL: ANALYZED (RANGE SCAN) OF 'OE_HDR_2'
(NON-UNIQUE)
197 VIEW OF 'AR_SALESPERSON_CODE'
197 SORT (UNIQUE)
197 SORT (GROUP BY)
197 HASH JOIN
212 TABLE ACCESS GOAL: ANALYZED (FULL) OF
'CT_TEAM_MEMBER'
5637 TABLE ACCESS GOAL: ANALYZED (FULL) OF
'CT_ADD_NAMES'
11 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID)
OF 'OE_LINE'
11 INDEX GOAL: ANALYZED (RANGE SCAN) OF 'OE_LINE_PK'
(UNIQUE)
16 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'OE_SUB_ENTITY'
16 INDEX GOAL: ANALYZED (UNIQUE SCAN) OF
'HM_OE_SUB_ENTITY_UK1' (UNIQUE)
8 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF
'HM_INVOICE_SUB_ENTITY_CONTROL'
16 INDEX GOAL: ANALYZED (UNIQUE SCAN) OF
'HM_INVOICE_SE_CONTROL_PK' (UNIQUE)
0 VIEW
1891480 SORT (GROUP BY)
237018 NESTED LOOPS
2 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'OE_CONTROL'
237018 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'AR_DOC_LINE'
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