RE: Nested Loop Semi Join
- From: "Lex de Haan" <lex.de.haan@xxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 30 Jun 2004 19:55:46 +0200
Hi Subbiah,
it might be 10x slower, but the estimated costs are all very similar: all
around 1800.
apparently, the CBO "slightly" overestimates the advantages of the semi-join
in your case :-)
by the way, I actually think the SEMI JOIN plan looks very elegant too,
compared with the 8i plan -- but who cares about elegant execution plans,
right?
Kind regards,
Lex.
---------------------------------------------
visit my website at http://www.naturaljoin.nl
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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Subbiah, Stalin
Sent: Wednesday, June 30, 2004 18:36
To: oracle-l@xxxxxxxxxxxxx
Subject: Nested Loop Semi Join
Has anyone seen this behavior on sql's with IN subqueries go into nested
loop semi join which is 10x times slower than 8174. However after hinting
with /*+ ordered no_expand */ I get much better performance than 8i.
Query in 8i with explain plan.
SQL> select count(*) from hffact where page_hit_key in (select page_hit_key
from page_hit where account_key=21152);
COUNT(*)
----------
40441
Elapsed: 00:01:28.59
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=12814 Card=1 Bytes=19)
1 0 SORT (AGGREGATE)
2 1 HASH JOIN (Cost=12814 Card=3852 Bytes=73188)
3 2 VIEW OF 'VW_NSO_1' (Cost=16 Card=125 Bytes=1625)
4 3 SORT (UNIQUE) (Cost=16 Card=125 Bytes=1375)
5 4 INDEX (RANGE SCAN) OF 'PAGE_HIT_WH_U1' (UNIQUE) (Cost=3
Card=126 Bytes=1386)
6 2 TABLE ACCESS (FULL) OF 'HFFACT' (Cost=12788 Card=34385176
Bytes=206311056)
Query in 9205 with optimizer_features_enable=920, cpu_costing = off
SQL> select count(*) from hffact where page_hit_key in (select page_hit_key
from page_hit where account_key=21152);
COUNT(*)
----------
40539
Elapsed: 00:13:59.22
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=12791 Card=1 Bytes=17)
1 0 SORT (AGGREGATE)
2 1 NESTED LOOPS (SEMI) (Cost=12791 Card=3883 Bytes=66011)
3 2 TABLE ACCESS (FULL) OF 'HFFACT' (Cost=12789 Card=34385176
Bytes=206311056)
4 2 INDEX (UNIQUE SCAN) OF 'PAGE_HIT_WH_U1' (UNIQUE)
Query in 9205 with optimizer_features_enable=920, cpu_costing = off, after
hinting
SQL> select /*+ ordered no_expand */ count(*) from hffact where page_hit_key
in (select page_hit_key from page_hit where account_key=21152);
COUNT(*)
----------
40539
Elapsed: 00:01:10.56
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=12816 Card=1 Bytes=17)
1 0 SORT (AGGREGATE)
2 1 HASH JOIN (Cost=12816 Card=3858 Bytes=65586)
3 2 SORT (UNIQUE)
4 3 INDEX (RANGE SCAN) OF 'PAGE_HIT_WH_U1' (UNIQUE) (Cost=3
Card=125 Bytes=1375)
5 2 TABLE ACCESS (FULL) OF 'HFFACT' (Cost=12789 Card=34385176
Bytes=206311056)
Thanks,
Stalin
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