CONCATENATION 引发的性能问题

背景是在一台11gR2的机器上，开发反映一个批处理比以前慢了3倍。经过仔细查看该SQL的执行计划，发现由于SQL中使用了or，导致CBO走出了一个非常糟糕的CONCATENATION路径。

no_expand提示的说明是 

The NO_EXPAND hint prevents the cost-based optimizer from considering OR-expansion for queries having OR conditions or IN-lists in the WHERE clause. Usually, 

the optimizer considers using OR expansion and uses this method if it decides that the cost is lower than not using it.

use_concat提示的说明是

The USE_CONCAT hint forces combined OR conditions in the WHERE clause of a query to be transformed into a compound query using the UNION ALL set operator. 

Generally, this transformation occurs only if the cost of the query using the concatenations is cheaper than the cost without them.

为了重现这个问题，必须使用/*+ use_concat */来模拟。

explain plan for SELECT  /*+ use_concat */
           20130620,
           B.mgr_code   ,
           B.mgr_name   ,
           B.cur_name   ,
           '3.4.2'   ,
           nvl(sum(ADJUST_AMT_AF),0) as acct_bal  ,
           nvl(sum(D_CMP_BAL),0)  ,
           nvl(sum(M_CMP_BAL),0)  ,
           nvl(sum(Y_CMP_BAL),0)  ,
           nvl(sum(Y_avg_af),0) as Y_avg_bal,
           B.cur_code,
           B.unit1_code,
           B.unit2_code,
           B.unit3_code,
           B.dept1_code,
           A.idx_name
        FROM S_PM_IDX_CODE A,T_PM_ACCT_DTL_AF B
        where  B.ACCT_FLAG in('OPEN','LOAN')
          AND  A.ROWID='AABK8vAAyAAGg/2AAs'
          AND  SUBSTR(B.FLAG,1,1) IN ('3')
          AND  SUBSTR(B.FLAG,2,1) IN ('2')
          AND  SUBSTR(B.FLAG,3,1) IN ('2')
          AND  1=1
          AND  1=1
          AND  1=1
          AND  1=1
          AND  1=1
          AND  1=1
          AND  1=1
          and ((A.term_flag is null)
                 or (A.term_flag is not null and A.begin_term<B.term
          and A.end_term >= B.term and B.term_flag = A.term_flag))
          AND B.data_date = 20130620
        group by B.mgr_code, B.mgr_name,
          B.cur_code, B.cur_name,
          B.unit1_code,B.unit2_code,
          B.unit3_code,
          B.dept1_code,
          A.IDX_NAME;

Plan hash value: 542663423

------------------------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name             | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |                  |     1 |   240 | 47236   (1)| 00:09:27 |       |       |
|   1 |  HASH GROUP BY                |                  |     1 |   240 |            |          |       |       |
|   2 |   CONCATENATION               |                  |       |       |            |          |       |       |
|   3 |    NESTED LOOPS               |                  |     1 |   240 | 23609   (1)| 00:04:44 |       |       |
|*  4 |     TABLE ACCESS BY USER ROWID| S_PM_IDX_CODE    |     1 |    97 |     1   (0)| 00:00:01 |       |       |
|   5 |     PARTITION LIST SINGLE     |                  |     1 |   143 | 23608   (1)| 00:04:44 |   KEY |   KEY |
|*  6 |      TABLE ACCESS FULL        | T_PM_ACCT_DTL_AF |     1 |   143 | 23608   (1)| 00:04:44 |   549 |   549 |
|   7 |    NESTED LOOPS               |                  |     1 |   240 | 23625   (1)| 00:04:44 |       |       |
|*  8 |     TABLE ACCESS BY USER ROWID| S_PM_IDX_CODE    |     1 |    97 |     1   (0)| 00:00:01 |       |       |
|   9 |     PARTITION LIST SINGLE     |                  |     1 |   143 | 23624   (1)| 00:04:44 |   KEY |   KEY |
|* 10 |      TABLE ACCESS FULL        | T_PM_ACCT_DTL_AF |     1 |   143 | 23624   (1)| 00:04:44 |   549 |   549 |
------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   4 - filter("A"."TERM_FLAG" IS NOT NULL)
   6 - filter("A"."BEGIN_TERM"<"B"."TERM" AND "A"."END_TERM">="B"."TERM" AND
              "B"."TERM_FLAG"="A"."TERM_FLAG" AND ("B"."ACCT_FLAG"='LOAN' OR "B"."ACCT_FLAG"='OPEN') AND
              SUBSTR("B"."FLAG",2,1)='2' AND SUBSTR("B"."FLAG",3,1)='2' AND SUBSTR("B"."FLAG",1,1)='3' AND
              "B"."DATA_DATE"=20130620)
   8 - filter("A"."TERM_FLAG" IS NULL)
  10 - filter(("B"."ACCT_FLAG"='LOAN' OR "B"."ACCT_FLAG"='OPEN') AND SUBSTR("B"."FLAG",2,1)='2' AND
              SUBSTR("B"."FLAG",3,1)='2' AND SUBSTR("B"."FLAG",1,1)='3' AND "B"."DATA_DATE"=20130620 AND
              (LNNVL("B"."TERM_FLAG"="A"."TERM_FLAG") OR LNNVL("A"."BEGIN_TERM"<"B"."TERM") OR
              LNNVL("A"."END_TERM">="B"."TERM") OR LNNVL("A"."TERM_FLAG" IS NOT NULL)))

Note
-----
   - dynamic sampling used for this statement (level=2)

explain plan for
 SELECT
           20130620,
           B.mgr_code   ,
           B.mgr_name   ,
           B.cur_name   ,
           '3.4.2'   ,
           nvl(sum(ADJUST_AMT_AF),0) as acct_bal  ,
           nvl(sum(D_CMP_BAL),0)  ,
           nvl(sum(M_CMP_BAL),0)  ,
           nvl(sum(Y_CMP_BAL),0)  ,
           nvl(sum(Y_avg_af),0) as Y_avg_bal,
           B.cur_code,
           B.unit1_code,
           B.unit2_code,
           B.unit3_code,
           B.dept1_code,
           A.idx_name
        FROM S_PM_IDX_CODE A,T_PM_ACCT_DTL_AF B
        where  B.ACCT_FLAG in('OPEN','LOAN')
          AND  A.ROWID='AABK8vAAyAAGg/2AAs'
          AND  SUBSTR(B.FLAG,1,1) IN ('3')
          AND  SUBSTR(B.FLAG,2,1) IN ('2')
          AND  SUBSTR(B.FLAG,3,1) IN ('2')
          AND  1=1
          AND  1=1
          AND  1=1
          AND  1=1
          AND  1=1
          AND  1=1
          AND  1=1
          and ((A.term_flag is null)
                 or (A.term_flag is not null and A.begin_term<B.term
          and A.end_term >= B.term and B.term_flag = A.term_flag))
          AND B.data_date = 20130620
        group by B.mgr_code, B.mgr_name,
          B.cur_code, B.cur_name,
          B.unit1_code,B.unit2_code,
          B.unit3_code,
          B.dept1_code,
          A.IDX_NAME;
select * from table(dbms_xplan.display());
Plan hash value: 2396922436

------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                            | Name                  | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                     |                       |     1 |   240 |  8058   (1)| 00:01:37 |       |       |
|   1 |  HASH GROUP BY                       |                       |     1 |   240 |  8058   (1)| 00:01:37 |       |       |
|   2 |   NESTED LOOPS                       |                       |     1 |   240 |  8057   (1)| 00:01:37 |       |       |
|   3 |    TABLE ACCESS BY USER ROWID        | S_PM_IDX_CODE         |     1 |    97 |     1   (0)| 00:00:01 |       |       |
|   4 |    PARTITION LIST SINGLE             |                       |     1 |   143 |  8056   (1)| 00:01:37 |   KEY |   KEY |
|*  5 |     TABLE ACCESS BY LOCAL INDEX ROWID| T_PM_ACCT_DTL_AF      |     1 |   143 |  8056   (1)| 00:01:37 |   549 |   549 |
|*  6 |      INDEX RANGE SCAN                | T_PM_ACCT_DTL_AF_IDX1 | 35022 |       |   136   (1)| 00:00:02 |   549 |   549 |
------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   5 - filter(("B"."ACCT_FLAG"='LOAN' OR "B"."ACCT_FLAG"='OPEN') AND SUBSTR("B"."FLAG",2,1)='2' AND
              SUBSTR("B"."FLAG",3,1)='2' AND ("A"."TERM_FLAG" IS NULL OR "B"."TERM_FLAG"="A"."TERM_FLAG" AND
              "A"."BEGIN_TERM"<"B"."TERM" AND "A"."END_TERM">="B"."TERM" AND "A"."TERM_FLAG" IS NOT NULL))
   6 - access(SUBSTR("FLAG",1,1)='3')

Note
-----
   - dynamic sampling used for this statement (level=2)