Oracle SQL 执行计划差异

Question

我有以下查询，我正在为它生成执行计划：

（编辑：我正在使用 SQL Developer）。

EXPLAIN PLAN
    FOR
WITH aux AS (
    SELECT
        *
    FROM
        cdc.uap_fkkvkp@rbip
    WHERE
        ezawe = 'D'
)
SELECT /* FULL(a) FULL(b) */
--    COUNT(1)
    b.zzpayment_plan,
    b.vkont,
    b.gpart,
    a.opbel,
    a.opupw,
    a.opupk,
    a.opupz,
    a.blart,
    a.betrw
FROM
    cdc.uap_dfkkop@rbip   a
    JOIN aux                   b ON b.vkont = a.vkont
WHERE
    a.augst IS NULL
    AND a.xanza IS NULL
    AND a.stakz IS NULL
    AND a.augrs IS NULL
    AND a.abwtp IS NULL;
    
SELECT
    *
FROM
    TABLE ( dbms_xplan.display );

它给出了以下计划：

Plan hash value: 289441478
 
-----------------------------------------------------------------------------------------------------------------------
| Id  | Operation                            | Name                   | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                     |                        |  4404K|   634M|       |  6752K  (1)| 00:04:24 |
|*  1 |  HASH JOIN                           |                        |  4404K|   634M|   291M|  6752K  (1)| 00:04:24 |
|*  2 |   TABLE ACCESS STORAGE FULL          | UAP_FKKVKP             |  4487K|   239M|       |   559K  (1)| 00:00:22 |
|*  3 |   TABLE ACCESS BY INDEX ROWID BATCHED| UAP_DFKKOP             |  4404K|   399M|       |  6160K  (1)| 00:04:01 |
|   4 |    BITMAP CONVERSION TO ROWIDS       |                        |       |       |       |            |          |
|   5 |     BITMAP AND                       |                        |       |       |       |            |          |
|*  6 |      BITMAP INDEX SINGLE VALUE       | UAP_DFKKOP_AUGST_2     |       |       |       |            |          |
|*  7 |      BITMAP INDEX SINGLE VALUE       | UAP_DFKKOP_NEW_STAKZ_2 |       |       |       |            |          |
|*  8 |      BITMAP INDEX SINGLE VALUE       | UAP_DFKKOP_AUGRS_2     |       |       |       |            |          |
-----------------------------------------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   1 - access("UAP_FKKVKP"."VKONT"="A"."VKONT")
   2 - storage("EZAWE"=U'D')
       filter("EZAWE"=U'D')
   3 - filter("A"."XANZA" IS NULL AND "A"."ABWTP" IS NULL)
   6 - access("A"."AUGST" IS NULL)
   7 - access("A"."STAKZ" IS NULL)
   8 - access("A"."AUGRS" IS NULL)
 
Note
-----
   - dynamic statistics used: dynamic sampling (level=2)
   - 1 Sql Plan Directive used for this statement

但是，如果我为代码的第一部分生成计划，但对于 COUNT(1) 未注释（以及其他选项已注释），则显示如下（与之前的执行计划完全相同）：

Plan hash value: 2732266276
 
------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                             | Name                   | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                      |                        |     1 |    66 |       |  6736K  (1)| 00:04:24 |
|   1 |  SORT AGGREGATE                       |                        |     1 |    66 |       |            |          |
|*  2 |   HASH JOIN                           |                        |  4404K|   277M|   171M|  6736K  (1)| 00:04:24 |
|*  3 |    TABLE ACCESS STORAGE FULL          | UAP_FKKVKP             |  4487K|   119M|       |   559K  (1)| 00:00:22 |
|*  4 |    TABLE ACCESS BY INDEX ROWID BATCHED| UAP_DFKKOP             |  4404K|   159M|       |  6160K  (1)| 00:04:01 |
|   5 |     BITMAP CONVERSION TO ROWIDS       |                        |       |       |       |            |          |
|   6 |      BITMAP AND                       |                        |       |       |       |            |          |
|*  7 |       BITMAP INDEX SINGLE VALUE       | UAP_DFKKOP_AUGST_2     |       |       |       |            |          |
|*  8 |       BITMAP INDEX SINGLE VALUE       | UAP_DFKKOP_NEW_STAKZ_2 |       |       |       |            |          |
|*  9 |       BITMAP INDEX SINGLE VALUE       | UAP_DFKKOP_AUGRS_2     |       |       |       |            |          |
------------------------------------------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   2 - access("UAP_FKKVKP"."VKONT"="A"."VKONT")
   3 - storage("EZAWE"=U'D')
       filter("EZAWE"=U'D')
   4 - filter("A"."XANZA" IS NULL AND "A"."ABWTP" IS NULL)
   7 - access("A"."AUGST" IS NULL)
   8 - access("A"."STAKZ" IS NULL)
   9 - access("A"."AUGRS" IS NULL)
 
Note
-----
   - dynamic statistics used: dynamic sampling (level=2)
   - 1 Sql Plan Directive used for this statement

如果我尝试执行这两个查询，第一个大约需要 3 秒，而第二个大约需要 8 分钟。

1. 为什么两者之间会有这样的差异，为什么没有在执行计划中捕获？
2. 我的全表扫描是否正确应用了？如果不是，最好的提示是什么？
3. 什么是最好的（最新的）书籍/文档/在线教程来提升我的 SQL 性能技能？到目前为止，我已经看到 Oracle 有一个性能开发健身房，还有一些书籍，如 Advanced Oracle SQL Tuning，看起来很有趣。

Answer 1

有了解释就没有真正的执行。在会话级别将 statistics_level 设置为 ALL 后，您将收到更多关于实际执行的详细信息。 但是在 SQLPLUS 中运行它：

set serverout off
alter session set statistics_level=all;

<execute the query here without explain>

select * from table(dbms_xplan.display_cursor(null,null,'RUNSTATS_LAST')); 

如果您提供两个这样的计划而不是 EXPLAIN PLAN，那么您的读者会更容易。 重要列的简短描述（Tanel Poder 网站不错）：

Starts - number of execution of the step
A-Rows - actual number of rows received from this step
Buffers - number of reads from RAM - you have to decrease this value
Reads - number of reads from disk
Writes - number of writes to disk - different from 0 - mainly for SELECTs when TEMP is used 

此计划使用方法示例如下：https://tanelpoder.com/files/Oracle_SQL_Plan_Execution.pdf