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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Horrendous Execution Plan from CBO
When were statistics last generated?
Any significant DML since then?
Jared
"Stahlke, Mark" <mstahlke_at_denvernewspaperagency.com>
Sent by: root_at_fatcity.com
06/07/2002 02:51 PM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
cc:
Subject: Horrendous Execution Plan from CBO
Greetings,
One of our developers came to me with a fairly simple query that runs much faster when she uses the RBO. I looked at the execution plans generated by both the RBO and CBO and the CBO's plan is horrible. I was able to get a reasonable plan from the CBO using a USE_NL hint.
Do any of you SQL tuning gurus have any suggestions? I've listed all the gory details below.
Thanks,
Mark Stahlke
Oracle DuhBA
Denver Newspaper Agency
The Gory Details:
Background:
Oracle 7.3.4 (I know, I know). PUB has 531324 rows. CNR has 601007 rows.
Both tables analyzed.
The Query:
1 SELECT
2 c.acct_key, 3 c.pub, 4 c.ref_nbr, 5 c.sls_nbr_1 cnr_sls_nbr, 6 p.sls_eff_iss_1, 7 p.sls_nbr_1_1, 8 p.sls_nbr_1_2, 9 p.sls_eff_iss_2, 10 p.sls_nbr_2_1, 11 p.sls_nbr_2_2, 12 p.sls_eff_iss_3, 13 p.sls_nbr_3_1, 14 p.sls_nbr_3_2
Plan and stats without hints:
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=28838 Card=597847 By
tes=100438296)
1 0 MERGE JOIN (Cost=28838 Card=597847 Bytes=100438296)
2 1 SORT (JOIN)
3 2 TABLE ACCESS (FULL) OF 'PUB' (Cost=841 Card=529489 Byt
es=55066856)
4 1 SORT (JOIN)
5 4 TABLE ACCESS (FULL) OF 'CNR' (Cost=2195 Card=598749 By
tes=38319936)
365 recursive calls
12740 db block gets
53167 consistent gets
96684 physical reads
4956 redo size
45285104 bytes sent via SQL*Net to client
441377 bytes received via SQL*Net from client
40070 SQL*Net roundtrips to/from client
0 sorts (memory)
2 sorts (disk)
601007 rows processed
Plan and stats with /*+ RULE */
Execution Plan
0 SELECT STATEMENT Optimizer=HINT: RULE 1 0 NESTED LOOPS
2 1 TABLE ACCESS (FULL) OF 'PUB' 3 1 TABLE ACCESS (BY ROWID) OF 'CNR' 4 3 INDEX (RANGE SCAN) OF 'PK_CNR' (UNIQUE)Statistics
0 recursive calls
4 db block gets
2828280 consistent gets
69635 physical reads
0 redo size
45285104 bytes sent via SQL*Net to client
441389 bytes received via SQL*Net from client
40070 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
601007 rows processed
Plan and stats with /*+ USE_NL(c p) */
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1204217 Card=601007
Bytes=100969176)
1 0 NESTED LOOPS (Cost=1204217 Card=601007 Bytes=100969176)
2 1 TABLE ACCESS (FULL) OF 'CNR' (Cost=2203 Card=601007 Byte
s=38464448)
3 1 TABLE ACCESS (BY ROWID) OF 'PUB' (Cost=844 Card=531324 B
ytes=55257696)
4 3 INDEX (UNIQUE SCAN) OF 'PK_PUB' (UNIQUE)
Statistics
0 recursive calls
4 db block gets
3062526 consistent gets
69490 physical reads
0 redo size
45285104 bytes sent via SQL*Net to client
441396 bytes received via SQL*Net from client
40070 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
601007 rows processed
-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Stahlke, Mark INET: mstahlke_at_denvernewspaperagency.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing ListsReceived on Fri Jun 07 2002 - 17:38:32 CDT
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