Question

我正在运行一个相对简单的查询

SELECT * FROM confirm_v c
JOIN person p ON c.created_by=p.id
INNER JOIN invoice_confirm ic ON ic.confirm_id=c.id
WHERE c.id = (SELECT id FROM 
                 (SELECT c2.id FROM confirm c2
                  JOIN invoice_confirm ic2 ON ic2.confirm_id=c2.id
                  WHERE ic2.invoice_id=11954081
                  AND c2.previous=0
                  AND c2.canceled=0
                  AND c2.confirm_type='INVOICE'
                  ORDER BY c2.id)
              WHERE rownum=1);

导致rdb 100％使用cpu。 confirm_type为varchar2(50 char)，其余为number(10)，如果有任何意义的话。

索引涵盖了invoice_confirm和confirm表，并且在此查询的执行计划中没有可见的完整表扫描。

此查询未执行很多，但占CPU总使用量的近100％。任何想法都表示赞赏。

编辑：来自查询的文本解释计划。

EXPLAIN PLAN FOR ...
SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());
Plan hash value: 1705859247


------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                                      | Name                        | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                               |                             |     1 |    69 |    10   (0)| 00:00:01 |
|   1 |  NESTED LOOPS                                  |                             |     1 |    69 |    10   (0)| 00:00:01 |
|   2 |   NESTED LOOPS                                 |                             |     1 |    69 |    10   (0)| 00:00:01 |
|   3 |    NESTED LOOPS                                |                             |     1 |    57 |     7   (0)| 00:00:01 |
|   4 |     NESTED LOOPS                               |                             |     1 |    30 |     5   (0)| 00:00:01 |
|   5 |      TABLE ACCESS BY INDEX ROWID               | CONFIRM                     |     1 |    24 |     3   (0)| 00:00:01 |
|*  6 |       INDEX UNIQUE SCAN                        | PK_CONFIRM                  |     1 |       |     2   (0)| 00:00:01 |
|*  7 |        COUNT STOPKEY                           |                             |       |       |            |          |
|   8 |         VIEW                                   |                             |     4 |    52 |    27   (4)| 00:00:01 |
|*  9 |          SORT ORDER BY STOPKEY                 |                             |     4 |   132 |    27   (4)| 00:00:01 |
|  10 |           NESTED LOOPS                         |                             |     4 |   132 |    26   (0)| 00:00:01 |
|  11 |            NESTED LOOPS                        |                             |    11 |   132 |    26   (0)| 00:00:01 |
|  12 |             TABLE ACCESS BY INDEX ROWID BATCHED| INVOICE_CONFIRM             |     3 |    36 |     4   (0)| 00:00:01 |
|* 13 |              INDEX RANGE SCAN                  | FKI_INVOICE_CONFIRM_INVOICE |     2 |       |     3   (0)| 00:00:01 |
|* 14 |             INDEX UNIQUE SCAN                  | PK_CONFIRM                  |     1 |       |     1   (0)| 00:00:01 |
|* 15 |            TABLE ACCESS BY INDEX ROWID         | CONFIRM                     |     1 |    21 |     2   (0)| 00:00:01 |
|* 16 |      INDEX RANGE SCAN                          | FKI_INVOICE_CONFIRM_CONFIRM |     1 |     6 |     2   (0)| 00:00:01 |
|  17 |     TABLE ACCESS BY INDEX ROWID                | PERSON                      |     1 |    27 |     2   (0)| 00:00:01 |
|* 18 |      INDEX UNIQUE SCAN                         | PK_KASUTAJA                 |     1 |       |     1   (0)| 00:00:01 |
|* 19 |    INDEX RANGE SCAN                            | FKI_INVOICE_CONFIRM_CONFIRM |     1 |       |     2   (0)| 00:00:01 |
|  20 |   TABLE ACCESS BY INDEX ROWID                  | INVOICE_CONFIRM             |     1 |    12 |     3   (0)| 00:00:01 |
------------------------------------------------------------------------------------------------------------------------------

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

   6 - access("CONFIRM"."ID"= (SELECT "ID" FROM  (SELECT "C2"."ID" "ID" FROM "INVOICE_CONFIRM" "IC2","CONFIRM" "C2" 
              WHERE "IC2"."CONFIRM_ID"="C2"."ID" AND "C2"."CANCELED"=0 AND "C2"."PREVIOUS"=0 AND "C2"."CONFIRM_TYPE"='INVOICE' AND 
              "IC2"."INVOICE_ID"=11954081 ORDER BY "C2"."ID") "from$_subquery$_006" WHERE ROWNUM=1))
   7 - filter(ROWNUM=1)
   9 - filter(ROWNUM=1)
  13 - access("IC2"."INVOICE_ID"=11954081)
  14 - access("IC2"."CONFIRM_ID"="C2"."ID")
  15 - filter("C2"."CANCELED"=0 AND "C2"."PREVIOUS"=0 AND "C2"."CONFIRM_TYPE"='INVOICE')
  16 - access("IC"."CONFIRM_ID"="CONFIRM"."ID")
  18 - access("CONFIRM"."CREATED_BY"="P"."ID")
  19 - access("IC"."CONFIRM_ID"="CONFIRM"."ID")

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)
   - 2 Sql Plan Directives used for this statement

Answer 1

收集相关表格的优化程序统计信息，并调查缺少统计信息的原因。

dynamic statistics used: dynamic sampling (level=2)

优化程序统计信息对于Oracle实现良好性能至关重要。注释select * from dba_optstat_operations where operation like '%auto%' order by start_time desc;表示存在缺少优化程序统计信息的表。除非在最后一天内创建表格，否则不应该发生这种情况。

Oracle会自动收集陈旧和缺失的统计信息。使用此查询检查作业是否正在运行。如果没有最近的行，请让您的DBA重新启用该任务。

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自动任务对大多数表来说已经足够了。但是，如果有一个大型批处理过程会更新很多行，那么应该在作业完成后立即手动收集统计信息。

Oracle SQL索引查询100％cpu使用率

1 个答案: