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稳定ORACLE的执行计划

日期:2019-04-19点击:297

原文发表在:http://l4j.cc/2019/04/19/oracle-sql-plan-management/

很多时候可能我们都希望CBO能够帮我们生成正确、高效的执行计划,但是很多时候事实并非如此,可能因为各种各样的原因(如,统计信息不正确或者CBO天生的缺陷等)都会导致生成的执行计划特别的低效。之前的一家公司有一台专门用于批量做数据校验清洗的数据库,每次校验清洗完成数据就会清理掉,统计信息经常会发生较大的变更,之前跑得好好的SQL,可能有时候跑5-6个小时都跑不完了,这时候查看执行计划,发现不正确的统计信息导致了执行计划的变更。

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这时候我们就希望数据库中运行的SQL都能有正确、稳定的执行计划,在10g开始的版本中可以通过SQL Profile来稳定执行计划或者在不改变SQL的情况下修改执行计划。11g开始可以使用偏主动的稳定执行计划的手段——SPM(SQL PLAN MANAGEMENT),保证只有被验证过的执行计划才会被启用。

SQL Profile

SQL Profile是包含特定于SQL语句的辅助统计信息的数据库对象,可以改进优化器基数估计,从而选择更好的执行计划。 当选择执行计划时优化器会考虑以下信息:

  1. SQL Profile提供的辅助统计信息
  2. 当时SQL的运行环境,如数据库配置,变量绑定,与优化器相关的统计信息等。

所以,上面两个条件的任意一个发生变化,都有可能导致执行计划的改变。下面看下SQL Profile的一些基本操作以及如何在线进行SQL的调整。

accepting sql profile

通过DBMS_SQLTUNE.ACCEPT_SQL_PROFILE存储过程可以接受一个SQL Profile,只有在我们接受了一个SQL Profile之后,优化器才能使用他作为产生执行计划的输入。这个存储过程有两个比较重要的参数:

  • profile_type 这个参数用于控制是否改变并行执行行为,REGULAR_PROFILE 不更改为并行执行,PX_PROFLE 用于更改并行执行的SQL Profile。
  • force_match 该参数用于控制SQL语句匹配,有两个值——TRUE和FALSE。对于SQL语句中where条件的字面值,当force_match=TRUE时,会将其替换为变量绑定,所以当字面值不同时也可以重用该SQL Profile。值为FALSE时,where条件的字面值则不会替换。

下面是ACCEPT_SQL_PROFILE的例子:

DECLARE my_sqlprofile_name VARCHAR2(30); BEGIN my_sqlprofile_name := DBMS_SQLTUNE.ACCEPT_SQL_PROFILE ( task_name => 'STA_SPECIFIC_EMP_TASK' , name => 'my_sql_profile' , profile_type => DBMS_SQLTUNE.PX_PROFILE , force_match => true ); END; / 

Listing SQL Profile

可以通过DBA_SQL_PROFILES数据字典视图来查看存储在数据库中的SQL Profile。

SQL> SELECT NAME,CATEGORY,SQL_TEXT,FORCE_MATCHING,STATUS FROM DBA_SQL_PROFILES; NAME CATEGORY SQL_TEXT FOR STATUS ------------------------------ ---------- ------------------------- --- -------- SYS_SQLPROF_016986bccd640000 DEFAULT select /*+ use_nl(a b) in NO ENABLED dex(b) */a.brwyid,a.yljgd m,a.jzlsh,b.mzzddm from t est_e 

Altering SQL Profile

通过ALTER_SQL_PROFILE中的attribute_name参数可以修改SQL Profile相应的参数值。

BEGIN DBMS_SQLTUNE.ALTER_SQL_PROFILE ( name => 'my_sql_profile' , attribute_name => 'FORCE_MATCH' , value => 'TRUE' ); END; / 

Droping SQL Profile

通过DROP_SQL_PROFILE存储过程可以删除特定的SQL Profile

BEGIN DBMS_SQLTUNE.DROP_SQL_PROFILE ( name => 'my_sql_profile' ); END; / 

通过SQL Profile调整线上SQL执行计划

通过手工创建SQL Profile的方式,可以在不更改目标SQL的SQL文本的情况下修改SQL的执行计划,而且可以很好的稳定SQL的执行计划。 下面是手工创建SQL Profile的例子,在TEST_ENV.TB_TABLE_LIST的列TABLE_NAME上有一个名为IDX_TB_TABLE_LIST_TBNAME的B树索引: 1、首先加一个全表扫描的HINTS来执行下面的SQL,模拟线上的一个执行低效的SQL,并查看其执行计划。

SQL> SELECT /*+FULL(T)*/ TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME ------------------------------ ACCESS$ SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL, NULL, 'advanced')); PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- SQL_ID 1a319c1c2b3rz, child number 0 ------------------------------------- SELECT /*+FULL(T)*/ TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Plan hash value: 1475094007 ----------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 31 (100)| | PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- |* 1 | TABLE ACCESS FULL| TB_TABLE_LIST | 1 | 18 | 31 (0)| 00:00:01 | ----------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id): ------------------------------------------------------------- 1 - SEL$1 / T@SEL$1 Outline Data ------------- PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS OPTIMIZER_FEATURES_ENABLE('18.1.0') DB_VERSION('18.1.0') ALL_ROWS OUTLINE_LEAF(@"SEL$1") FULL(@"SEL$1" "T"@"SEL$1") END_OUTLINE_DATA */ PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("TABLE_NAME"='ACCESS$') Column Projection Information (identified by operation id): ----------------------------------------------------------- 1 - (rowset=256) "TABLE_NAME"[VARCHAR2,128] 已选择 43 行。 

2、然后加入走索引的HINTS来更正这个SQL的执行计划,得到下面的执行计划相关信息,此时我们就需要用这个执行计划来替换掉上面走全表扫描的SQL的执行计划。

SQL> SELECT /*+ INDEX(T IDX_TB_TABLE_LIST_TBNAME) */TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME ------------------------------ ACCESS$ SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL, NULL, 'advanced')); PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- SQL_ID 44j1ysb93cwdq, child number 0 ------------------------------------- SELECT /*+ INDEX(T IDX_TB_TABLE_LIST_TBNAME) */TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Plan hash value: 3318876060 --------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 1 (100)| | PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- |* 1 | INDEX RANGE SCAN| IDX_TB_TABLE_LIST_TBNAME | 1 | 18 | 1 (0)| 00:00:01 | --------------------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id): ------------------------------------------------------------- 1 - SEL$1 / T@SEL$1 Outline Data ------------- PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS OPTIMIZER_FEATURES_ENABLE('18.1.0') DB_VERSION('18.1.0') ALL_ROWS OUTLINE_LEAF(@"SEL$1") INDEX(@"SEL$1" "T"@"SEL$1" ("TB_TABLE_LIST"."TABLE_NAME")) END_OUTLINE_DATA */ PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("TABLE_NAME"='ACCESS$') Column Projection Information (identified by operation id): ----------------------------------------------------------- 1 - "TABLE_NAME"[VARCHAR2,128] 已选择 43 行。 

3、下面查看对应的SQL_ID。

SQL> SELECT SQL_TEXT,SQL_ID FROM V$SQLAREA WHERE SQL_TEXT LIKE '%TABLE_NAME FROM TEST_ENV.TB_TABLE%'; SQL_TEXT SQL_ID ------------------------- ------------- SELECT /*+ INDEX(T IDX_TB 44j1ysb93cwdq _TABLE_LIST_TBNAME) */TAB LE_NAME FROM TEST_ENV.TB_ TABLE_LIST T WHERE TABLE_ NAME='ACCESS$' SELECT SQL_TEXT,SQL_ID FR g4v1sg4ycf96y OM V$SQLAREA WHERE SQL_TE XT LIKE '%TABLE_NAME FROM TEST_ENV.TB_TABLE%' SQL_TEXT SQL_ID ------------------------- ------------- SELECT /*+FULL(T)*/ TABLE 1a319c1c2b3rz _NAME FROM TEST_ENV.TB_TA BLE_LIST T WHERE TABLE_NA ME='ACCESS$' 

4、创建SQL PROFILE,用正确的执行计划的OUT LINE DATA来创建SQL Profile

SQL> declare 2 v_hints sys.sqlprof_attr; 3 clsql_text clob; 4 begin 5 v_hints := sys.sqlprof_attr('BEGIN_OUTLINE_DATA', 6 'IGNORE_OPTIM_EMBEDDED_HINTS', 7 'OPTIMIZER_FEATURES_ENABLE(''18.1.0'')', 8 'DB_VERSION(''18.1.0'')', 9 'ALL_ROWS', 10 'OUTLINE_LEAF(@"SEL$1")', 11 'INDEX(@"SEL$1" "T"@"SEL$1" ("TB_TABLE_LIST"."TABLE_NAME"))', 12 'END_OUTLINE_DATA'); 13 14 select sql_fulltext into clsql_text from v$sqlarea where sql_id='1a319c1c2b3rz'; 15 16 dbms_sqltune.import_sql_profile(clsql_text,v_hints,'my_sql_profile',force_match=>true,replace=>true); 17 end; 18 / PL/SQL 过程已成功完成。 

5、最后再来看加FULL这个HINTS的SQL语句的执行计划,可以看到此时已经是做的索引范围扫描了。

SQL> SELECT /*+FULL(T)*/ TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME ------------------------------ ACCESS$ SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL, NULL, 'advanced')); PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- SQL_ID 1a319c1c2b3rz, child number 0 ------------------------------------- SELECT /*+FULL(T)*/ TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Plan hash value: 3318876060 --------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 1 (100)| | PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- |* 1 | INDEX RANGE SCAN| IDX_TB_TABLE_LIST_TBNAME | 1 | 18 | 1 (0)| 00:00:01 | --------------------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id): ------------------------------------------------------------- 1 - SEL$1 / T@SEL$1 Outline Data ------------- PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS OPTIMIZER_FEATURES_ENABLE('18.1.0') DB_VERSION('18.1.0') ALL_ROWS OUTLINE_LEAF(@"SEL$1") INDEX(@"SEL$1" "T"@"SEL$1" ("TB_TABLE_LIST"."TABLE_NAME")) END_OUTLINE_DATA */ PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("TABLE_NAME"='ACCESS$') Column Projection Information (identified by operation id): ----------------------------------------------------------- 1 - "TABLE_NAME"[VARCHAR2,128] Note PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------- ----- - SQL profile my_sql_profile used for this statement 已选择 47 行。 

SPM

SQL Plan Management(SPM)可以有效避免执行计划变更而导致的性能下降的问题,只有被验证和接受的执行计划才是可用的。SPM采用了一种叫SQL PLAN BASELINE的机制,它是一系列被验证性能良好的SQL执行计划的集合。不管SQL Plan Baseline还是SQL Profile都是通过内部使用hints来实现的,他们之间的区别如下:

  1. SQL Plan BaseLine是一种偏主动的机制,可以在性能问题出现之前就创建SQL基线,避免优化器在未来某个时刻选择次优的执行计划。而SQL Profile只能等到发现SQL的性能问题时,调用SQL Tuning Advisor来对有问题的SQL进行调整。
  2. SQL Plan Baseline会从新产生一个具体的执行计划,不会随着其他相关统计信息的变更而变更,但是SQL Profile只是为优化器提供一个辅助信息。 SQL Plan Baseline的hints会指定生成一个具体的执行计划,但是SQL Profile的hints只是帮助调整优化器错误的计算

初始化参数配置

可以通过以下两个参数来控制SPM的行为:

  • OPTIMIZER_CAPTURE_SQL_PLAN_BASELINES=TRUE|FALSE 该参数用于控制是否启用自动捕获SQL Plan Baseline,默认值为FALSE。该参数可以在SESSION或者SYSTEM级别进行修改,修改为TRUE后,ORACLE会对其影响的范围内的所有重复执行的SQL自动捕获其SQL Plan Baseline。对于第一次捕获到的结果,其ENABLED和ACCEPTED的值均为'YES'。当执行计划变更,被再次捕获到时,其ENABLED=YES但是ACCEPTED的值为'NO',表示该SQL依然会使用第一次捕获到的SQL执行计划。
  • OPTIMIZER_USE_SQL_PLAN_BASELINES=TRUE|FALSE 该参数用于控制是否启用SQL Plan Baseline,默认值为TRUE,该参数也可以在SESSION和SYSTEM级别设置。

查看SQL Plan Baseline中的执行计划

通过数据字典DBA_SQL_PLAN_BASELINES可以查询到存储在数据库中的SQL Plan Baselines,然后使用DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE函数可以查看对应的执行计划。

SELECT SIGNATURE,SQL_TEXT,SQL_HANDLE,PLAN_NAME FROM DBA_SQL_PLAN_BASELINES; SELECT * from table(DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE('SQL_787830cec4402bdf','SQL_PLAN_7hy1htv240ayz01f095c0','advanced')); 

批量加载SQL Plan Baseline

通过DBMS_SPM包提供的相关函数,我们可以从SQL Tuning Set、 Shared SQL Area和Staging Table中加载SQL Plan Baseline。比较常用的是通过Staging Table的方式来进行不同数据库之间SQL Plan Baseline的迁移,比如我们在测试库中调试好了一批SQL,需要将其执行计划导入到生产库中。 下面是通过Staging Table方式将A库的SQL Plan Baseline迁移到B库的基本流程:

  1. 使用DBMS_SPM.CREATE_STGTAB_BASELINE创建中间表。
BEGIN DBMS_SPM.CREATE_STGTAB_BASELINE ( table_name => 'stage1'); END; / 
  1. 将SQL Plan Baseline打包到刚刚创建的中间表stage1
DECLARE v_plan_cnt NUMBER; BEGIN v_plan_cnt := DBMS_SPM.PACK_STGTAB_BASELINE ( table_name => 'stage1' , enabled => 'yes' , creator => 'spm' ); END; / 
  1. 将中间表传输到目标数据库中,可以通过数据泵等手段。
  2. 在目标库中,将中间表的数据解压。
DECLARE v_plan_cnt NUMBER; BEGIN v_plan_cnt := DBMS_SPM.UNPACK_STGTAB_BASELINE ( table_name => 'stage1' , fixed => 'yes' ); END; / 

删除SQL Plan Baseline

通过DBMS_SPM.DROP_SQL_PLAN_BASELINE函数可以删除已经保存的SQL Plan Baseline:

  1. 首先通过DBA_SQL_PLAN_BASELINES获取到对应的SQL_HANDLE
  2. 执行删除操作
SQL> EXEC DBMS_SPM.DROP_SQL_PLAN_BASELINE (sql_handle => 'SQL_b6b0d1c71cd1807b'); 

实例1——自动捕获

  1. 修改optimizer_capture_sql_plan_baselines参数启用自动捕获
SQL> alter system flush shared_pool; 系统已更改。 SQL> alter system flush buffer_cache; 系统已更改。 SQL> show parameter sql_plan NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ optimizer_capture_sql_plan_baselines boolean FALSE optimizer_use_sql_plan_baselines boolean TRUE SQL> alter system set optimizer_capture_sql_plan_baselines=TRUE; 系统已更改。 SQL> show parameter sql_pla NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ optimizer_capture_sql_plan_baselines boolean TRUE optimizer_use_sql_plan_baselines boolean TRUE 
  1. 第一次执行SQL,可以看到在DBA_SQL_PLAN_BASELINES中并未查到相应的SQL基线,再次执行才能查询到。
SQL> SET PAGES 10000 LINES 140 SQL> SET SERVEROUTPUT ON SQL> COL SQL_TEXT FOR A20 SQL> COL SQL_HANDLE FOR A20 SQL> COL PLAN_NAME FOR A30 SQL> COL ORIGIN FOR A12 SQL> COL TABLE_NAME FOR A20 SQL> SET LONGC 60535 SQL> SET LONG 60535 SQL> SET ECHO ON SQL> SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME -------------------- ACCESS$ SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED, FIXED, AUTOPURGE FROM DBA_SQL_PLAN_BASELINES W HERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; 未选定行 
  1. 再次执行上面的SQL。查询DBA_SQL_PLAN_BASELINES,对应的SQL Plan Baseline的ACCEPTED和ENABLE的值均为YES。
SQL> SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME -------------------- ACCESS$ SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED, FIXED, AUTOPURGE FROM DBA_SQL_PLAN_BASELINES W HERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC FIX AUT -------------------- -------------------- ------------------------------ ------------ --- --- --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayzc127edb7 AUTO-CAPTURE YES YES NO YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' 
  1. 在表上创建一个TABLE_NAME列的B-TREE索引,然后再次执行上面的SQL语句,通过DBA_SQL_PLAN_BASELINES查询,此时多了一条SQL Plan Baseline,ENABLE=YES,ACCEPTED=NO
SQL> CREATE INDEX test_env.IDX_TB_TABLE_LIST_TBNAME ON TEST_ENV.TB_TABLE_LIST(TABLE_NAME); 索引已创建。 SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS('TEST_ENV','TB_TABLE_LIST',CASCADE=>TRUE); PL/SQL 过程已成功完成。 SQL> SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME -------------------- ACCESS$ SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED, FIXED, AUTOPURGE FROM DBA_SQL_PLAN_BASELINES W HERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC FIX AUT -------------------- -------------------- ------------------------------ ------------ --- --- --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayz01f095c0 AUTO-CAPTURE YES NO NO YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayzc127edb7 AUTO-CAPTURE YES YES NO YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' 
  1. 在TABLE_NAME列创建索引之后,根据此列查询,应该是走INDEX RANGE SCAN,但是事实是怎么样呢?看下该语句的执行计划。
SQL> explain plan for SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; 已解释。 SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY(null, null, 'basic +note')); PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ -------------------- Plan hash value: 1475094007 ------------------------------------------- | Id | Operation | Name | ------------------------------------------- | 0 | SELECT STATEMENT | | | 1 | TABLE ACCESS FULL| TB_TABLE_LIST | ------------------------------------------- Note ----- - SQL plan baseline "SQL_PLAN_7hy1htv240ayzc127edb7" used for this statement 已选择 12 行。 

可以看到,执行这个SQL依然走的是全表扫描,注意note部分,表示这个执行计划使用了"SQL_PLAN_7hy1htv240ayzc127edb7"的SQL Plan Baseline。表明了SPM可以很好的固定特定SQL的执行计划。 6. 但是实际上此时应该是走索引范围扫描才是最高效的,即"SQL_PLAN_7hy1htv240ayz01f095c0"这个SQL Plan Baseline,如何启用改baseline呢?首先创建一个evole任务,并执行该任务。

SQL> var cnt NUMBER SQL> var tk_name VARCHAR2(50) SQL> var exe_name VARCHAR2(50) SQL> var evol_out CLOB SQL> EXEC :tk_name := DBMS_SPM.CREATE_EVOLVE_TASK(sql_handle => 'SQL_787830cec4402bdf', plan_name => 'SQL_PLAN_7hy1htv2 40ayz01f095c0'); PL/SQL 过程已成功完成。 SQL> print :tk_name TK_NAME -------- 任务_31 SQL> EXEC :exe_name :=DBMS_SPM.EXECUTE_EVOLVE_TASK(task_name=>:tk_name); PL/SQL 过程已成功完成。 SQL> print :exe_name EXE_NAME -------- EXEC_151 
  1. 执行完成之后,通过REPORT_EVOLVE_TASK可以查看到相应的任务报告。Findings部分告诉我们发现了一个比基线效率更高的执行计划,并提供了建议方案。
SQL> EXEC :evol_out := DBMS_SPM.REPORT_EVOLVE_TASK( task_name=>:tk_name, execution_name=>:exe_name ); PL/SQL 过程已成功完成。 SQL> SELECT :evol_out FROM DUAL; :EVOL_OUT ------------------------------------------------------------------------------------------------------------------------ -------------------- GENERAL INFORMATION SECTION --------------------------------------------------------------------------------------------- Task Information: --------------------------------------------- Task Name : 任务_31 Task Owner : SYS Execution Name : EXEC_151 Execution Type : SPM EVOLVE Scope : COMPREHENSIVE Status : COMPLETED Started : 04/19/2019 16:45:33 Finished : 04/19/2019 16:45:33 Last Updated : 04/19/2019 16:45:33 Global Time Limit : 2147483646 Per-Plan Time Limit : UNUSED Number of Errors : 0 --------------------------------------------------------------------------------------------- SUMMARY SECTION --------------------------------------------------------------------------------------------- Number of plans processed : 1 Number of findings : 1 Number of recommendations : 1 Number of errors : 0 --------------------------------------------------------------------------------------------- DETAILS SECTION --------------------------------------------------------------------------------------------- Object ID : 2 Test Plan Name : SQL_PLAN_7hy1htv240ayz01f095c0 Base Plan Name : SQL_PLAN_7hy1htv240ayzc127edb7 SQL Handle : SQL_787830cec4402bdf Parsing Schema : SYS Test Plan Creator : SYS SQL Text : SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Execution Statistics: ----------------------------- Base Plan Test Plan ---------------------------- ---------------------------- Elapsed Time (s): .000016 .000001 CPU Time (s): 0 0 Buffer Gets: 10 0 Optimizer Cost: 31 1 Disk Reads: 0 0 Direct Writes: 0 0 Rows Processed: 0 0 Executions: 10 10 FINDINGS SECTION --------------------------------------------------------------------------------------------- Findings (1): ----------------------------- 1. 计划已在 0.03200 秒内验证完毕。此计划符合收益标准, 这是因为其验证性能比基线计划的性能高 50.50000 倍。 Recommendation: ----------------------------- Consider accepting the plan. Execute dbms_spm.accept_sql_plan_baseline(task_name => '任务_31', object_id => 2, task_owner => 'SYS'); EXPLAIN PLANS SECTION --------------------------------------------------------------------------------------------- Baseline Plan ----------------------------- Plan Id : 201 Plan Hash Value : 3240619447 ------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost | Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 18 | 31 | 00:00:01 | | * 1 | TABLE ACCESS FULL | TB_TABLE_LIST | 1 | 18 | 31 | 00:00:01 | ------------------------------------------------------------------------------ Predicate Information (identified by operation id): ------------------------------------------ * 1 - filter("TABLE_NAME"='ACCESS$') Test Plan ----------------------------- Plan Id : 202 Plan Hash Value : 32544192 ---------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost | Time | ---------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 18 | 1 | 00:00:01 | | * 1 | INDEX RANGE SCAN | IDX_TB_TABLE_LIST_TBNAME | 1 | 18 | 1 | 00:00:01 | ---------------------------------------------------------------------------------------- Predicate Information (identified by operation id): ------------------------------------------ * 1 - access("TABLE_NAME"='ACCESS$') --------------------------------------------------------------------------------------------- 
  1. 可以通过上面报告中建议的方式来接受这个计划,也可以使用IMPLEMENT_EVOLVE_TASK函数。
SQL> EXEC :cnt := DBMS_SPM.IMPLEMENT_EVOLVE_TASK( task_name=>:tk_name, execution_name=>:exe_name ); PL/SQL 过程已成功完成。 SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED FROM DBA_SQL_PLAN_BASELINES WHERE SQL_HANDLE=' SQL_787830cec4402bdf'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC -------------------- -------------------- ------------------------------ ------------ --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayz01f095c0 AUTO-CAPTURE YES YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayzc127edb7 AUTO-CAPTURE YES YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' 
  1. 最后我们再来看下执行计划
 SQL> explain plan for SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; 已解释。 SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY(null, null, 'basic +note')); PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ Plan hash value: 3318876060 ----------------------------------------------------- | Id | Operation | Name | ----------------------------------------------------- | 0 | SELECT STATEMENT | | | 1 | INDEX RANGE SCAN| IDX_TB_TABLE_LIST_TBNAME | ----------------------------------------------------- Note ----- - SQL plan baseline "SQL_PLAN_7hy1htv240ayz01f095c0" used for this statement 已选择 12 行。 

可以看到此时已经走了索引范围扫描,使用的是"SQL_PLAN_7hy1htv240ayz01f095c0"这个SQL Plan Baseline。当存在多个计划的ACCEPTED和ENABLE的值都为YES的时候,优化器会选择一个成本更低的计划来执行。

实例2——手工生成

接下来看下手工生成SQL Plan Baseline的方法。其实非常简单,核心就是通过DBMS_STATS.LOAD_PLANS_FROM_CURSOR_CACHE来从Shared SQL Area中加载执行计划。

  1. 首先对前面例子生成的内容进行清理。
SQL> alter system set optimizer_capture_sql_plan_baselines=false; 系统已更改。 SQL> show parameter sql_pla NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ optimizer_capture_sql_plan_baselines boolean FALSE optimizer_use_sql_plan_baselines boolean TRUE SQL> EXEC :cnt :=DBMS_SPM.DROP_SQL_PLAN_BASELINE('SQL_787830cec4402bdf'); PL/SQL 过程已成功完成。 SQL> EXEC :cnt :=DBMS_SPM.DROP_SQL_PLAN_BASELINE('SQL_061becb140fad607'); PL/SQL 过程已成功完成。 SQL> EXEC :cnt :=DBMS_SPM.DROP_SQL_PLAN_BASELINE('SQL_ecca2815c7166fb6'); PL/SQL 过程已成功完成。 SQL> EXEC :cnt :=DBMS_SPM.DROP_SQL_PLAN_BASELINE('SQL_9049245213a986b3'); PL/SQL 过程已成功完成。 SQL> EXEC :cnt :=DBMS_SPM.DROP_SQL_PLAN_BASELINE('SQL_85372e07e425b213'); PL/SQL 过程已成功完成。 SQL> DELETE FROM SQLLOG$; 已删除 9 行。 SQL> commit; 提交完成。 SQL> alter system flush shared_pool; 系统已更改。 SQL> alter system flush buffer_cache; 系统已更改。 
  1. 执行SQL并查看执行计划
SQL> SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME -------------------- ACCESS$ SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL, NULL, 'advanced')); PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ SQL_ID drmkgq2ppg7kg, child number 0 ------------------------------------- SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Plan hash value: 1475094007 ----------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 31 (100)| | PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ |* 1 | TABLE ACCESS FULL| TB_TABLE_LIST | 1 | 18 | 31 (0)| 00:00:01 | ----------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id): ------------------------------------------------------------- 1 - SEL$1 / T@SEL$1 Outline Data ------------- PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS OPTIMIZER_FEATURES_ENABLE('18.1.0') DB_VERSION('18.1.0') ALL_ROWS OUTLINE_LEAF(@"SEL$1") FULL(@"SEL$1" "T"@"SEL$1") END_OUTLINE_DATA */ PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("TABLE_NAME"='ACCESS$') Column Projection Information (identified by operation id): ----------------------------------------------------------- 1 - (rowset=256) "TABLE_NAME"[VARCHAR2,128] 已选择 43 行。 
  1. 因为此时自动捕获是关闭的,所以不管执行多少次SQL,都没有对应的SQL Plan Baseline。可以手动的将对应的执行计划加入到SQL Plan Baseline中。
SQL> var cnt number SQL> exec :cnt := DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE(sql_id=>'drmkgq2ppg7kg', plan_hash_value=>'1475094007'); PL/SQL 过程已成功完成。 SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED FROM DBA_SQL_PLAN_BASELINES WHERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC -------------------- -------------------- ------------------------------ ------------ --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayzc127edb7 MANUAL-LOAD- YES YES OM TEST_ENV.TB_TABLE FROM-CURSOR- _LIST T WHERE TABLE_ CACHE NAME='ACCESS$' 
  1. 在TABLE_NAME列上创建索引,然后再次执行SQL,并查看执行计划。可以看到虽然在TABLE_NAME这个列上存在索引,但是已经存在对应SQL语句的一个走全表扫描的执行基线,所以此时依旧走的全表扫描,使用的是刚刚加载进去的'SQL_PLAN_7hy1htv240ayzc127edb7'这个SQL Plan Baseline。
SQL> SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME -------------------- ACCESS$ SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL, NULL, 'advanced')); PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------- SQL_ID drmkgq2ppg7kg, child number 1 ------------------------------------- SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Plan hash value: 1475094007 ----------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 31 (100)| | PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------- |* 1 | TABLE ACCESS FULL| TB_TABLE_LIST | 1 | 18 | 31 (0)| 00:00:01 | ----------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id): ------------------------------------------------------------- 1 - SEL$1 / T@SEL$1 Outline Data ------------- PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------- /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS OPTIMIZER_FEATURES_ENABLE('18.1.0') DB_VERSION('18.1.0') ALL_ROWS OUTLINE_LEAF(@"SEL$1") FULL(@"SEL$1" "T"@"SEL$1") END_OUTLINE_DATA */ PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("TABLE_NAME"='ACCESS$') Column Projection Information (identified by operation id): ----------------------------------------------------------- 1 - (rowset=256) "TABLE_NAME"[VARCHAR2,128] Note PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------- ----- - SQL plan baseline SQL_PLAN_7hy1htv240ayzc127edb7 used for this statement 已选择 47 行。 
  1. 这个时候我们再来查看下DBA_SQL_PLAN_BASELINES这个数据字典,可以看到SPM帮我们自动捕获了一条ENABLE为YES,ACCEPTED为NO的SQL Plan Baseline。
SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED FROM DBA_SQL_PLAN_BASELINES WHERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC -------------------- -------------------- ------------------------------ ------------ --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayz01f095c0 AUTO-CAPTURE YES NO OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayzc127edb7 MANUAL-LOAD- YES YES OM TEST_ENV.TB_TABLE FROM-CURSOR- _LIST T WHERE TABLE_ CACHE NAME='ACCESS$' 
  1. 将'SQL_PLAN_7hy1htv240ayz01f095c0'的ACCEPTED的值改为YES。
SQL> var result clob; SQL> EXEC :result :=DBMS_SPM.EVOLVE_SQL_PLAN_BASELINE(SQL_HANDLE=>'SQL_787830cec4402bdf', PLAN_NAME=>'SQL_PLAN_7hy1htv24 0ayz01f095c0', VERIFY=>'NO', COMMIT=>'YES'); PL/SQL 过程已成功完成。 SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED FROM DBA_SQL_PLAN_BASELINES WHERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC -------------------- -------------------- ------------------------------ ------------ --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayz01f095c0 AUTO-CAPTURE YES YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayzc127edb7 MANUAL-LOAD- YES YES OM TEST_ENV.TB_TABLE FROM-CURSOR- _LIST T WHERE TABLE_ CACHE NAME='ACCESS$' 
  1. 再次执行SQL,此时使用了'SQL_PLAN_7hy1htv240ayz01f095c0'这个SQL Plan Baseline了。
SQL> SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME -------------------- ACCESS$ SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL, NULL, 'advanced')); PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ SQL_ID drmkgq2ppg7kg, child number 0 ------------------------------------- SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Plan hash value: 3318876060 --------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 1 (100)| | PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ |* 1 | INDEX RANGE SCAN| IDX_TB_TABLE_LIST_TBNAME | 1 | 18 | 1 (0)| 00:00:01 | --------------------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id): ------------------------------------------------------------- 1 - SEL$1 / T@SEL$1 Outline Data ------------- PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS OPTIMIZER_FEATURES_ENABLE('18.1.0') DB_VERSION('18.1.0') ALL_ROWS OUTLINE_LEAF(@"SEL$1") INDEX(@"SEL$1" "T"@"SEL$1" ("TB_TABLE_LIST"."TABLE_NAME")) END_OUTLINE_DATA */ PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("TABLE_NAME"='ACCESS$') Column Projection Information (identified by operation id): ----------------------------------------------------------- 1 - "TABLE_NAME"[VARCHAR2,128] Note PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ ----- - SQL plan baseline SQL_PLAN_7hy1htv240ayz01f095c0 used for this statement 已选择 47 行。 
  1. 前面的SQL都是没有HINTS的,有时候我们需加入HINTS对SQL的执行计划进行调整。如何用加入了hints的SQL执行计划来替换之前的SQL,生成新的SQL Plan Baseline呢?首先删除之前做全表扫描的SQL Plan Baseline,然后加入一个FULL的hints来执行SQL,此时SQL_ID和之前是不同的。
SQL> exec :cnt :=DBMS_SPM.DROP_SQL_PLAN_BASELINE (sql_handle=>'SQL_787830cec4402bdf', plan_name=>'SQL_PLAN_7hy1htv240ayz c127edb7'); PL/SQL 过程已成功完成。 SQL> SELECT /*+FULL(T)*/ TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME -------------------- ACCESS$ SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL, NULL, 'advanced')); PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------------------------- SQL_ID 1a319c1c2b3rz, child number 0 ------------------------------------- SELECT /*+FULL(T)*/ TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Plan hash value: 1475094007 ----------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 31 (100)| | PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------------------------- |* 1 | TABLE ACCESS FULL| TB_TABLE_LIST | 1 | 18 | 31 (0)| 00:00:01 | ----------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id): ------------------------------------------------------------- 1 - SEL$1 / T@SEL$1 Outline Data ------------- PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------------------------- /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS OPTIMIZER_FEATURES_ENABLE('18.1.0') DB_VERSION('18.1.0') ALL_ROWS OUTLINE_LEAF(@"SEL$1") FULL(@"SEL$1" "T"@"SEL$1") END_OUTLINE_DATA */ PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("TABLE_NAME"='ACCESS$') Column Projection Information (identified by operation id): ----------------------------------------------------------- 1 - (rowset=256) "TABLE_NAME"[VARCHAR2,128] 已选择 43 行。 

此时从索引范围扫描变成了全表扫描,SQL_ID为1a319c1c2b3rz,PLAN_HASH_VALUE为1475094007 9. 此时的DBA_SQL_PLAN_BASELINES依然之后刚刚那一条记录。

SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED FROM DBA_SQL_PLAN_BASELINES WHERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC -------------------- -------------------- ------------------------------ ------------ --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayz01f095c0 AUTO-CAPTURE YES YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' 
  1. 现在用上述改写后的SQL的新的执行计划来手工生成SQL Plan Baseline
SQL> exec :cnt := dbms_spm.load_plans_from_cursor_cache(sql_id => '1a319c1c2b3rz', plan_hash_value=>1475094007, sql_handle=>'SQL_787830cec4402bdf') PL/SQL 过程已成功完成。 SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED FROM DBA_SQL_PLAN_BASELINES WHERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC -------------------- -------------------- ------------------------------ ------------ --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayz01f095c0 AUTO-CAPTURE YES YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayzc127edb7 MANUAL-LOAD- YES YES OM TEST_ENV.TB_TABLE FROM-CURSOR- _LIST T WHERE TABLE_ CACHE NAME='ACCESS$' 
  1. 由于此时所对应的SQL Plan Baseline的ENABLED和ACCEPTED的值都为YES,我们将之前的走索引范围扫描的ENABLED属性改为NO,然后执行SQL语句。
SQL> EXEC :CNT := DBMS_SPM.ALTER_SQL_PLAN_BASELINE(SQL_HANDLE=>'SQL_787830cec4402bdf', PLAN_NAME=>'SQL_PLAN_7hy1htv240ay z01f095c0', ATTRIBUTE_NAME=>'ENABLED', ATTRIBUTE_VALUE=>'NO'); PL/SQL 过程已成功完成。 SQL> SELECT SQL_HANDLE, SQL_TEXT, PLAN_NAME, ORIGIN, ENABLED, ACCEPTED FROM DBA_SQL_PLAN_BASELINES WHERE SQL_TEXT LIKE '%TEST_ENV.TB_TABLE_LIST%'; SQL_HANDLE SQL_TEXT PLAN_NAME ORIGIN ENA ACC -------------------- -------------------- ------------------------------ ------------ --- --- SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayz01f095c0 AUTO-CAPTURE NO YES OM TEST_ENV.TB_TABLE _LIST T WHERE TABLE_ NAME='ACCESS$' SQL_787830cec4402bdf SELECT TABLE_NAME FR SQL_PLAN_7hy1htv240ayzc127edb7 MANUAL-LOAD- YES YES OM TEST_ENV.TB_TABLE FROM-CURSOR- _LIST T WHERE TABLE_ CACHE NAME='ACCESS$' SQL> SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$'; TABLE_NAME -------------------- ACCESS$ SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL, NULL, 'advanced')); PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ SQL_ID drmkgq2ppg7kg, child number 1 ------------------------------------- SELECT TABLE_NAME FROM TEST_ENV.TB_TABLE_LIST T WHERE TABLE_NAME='ACCESS$' Plan hash value: 1475094007 ----------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 31 (100)| | PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ |* 1 | TABLE ACCESS FULL| TB_TABLE_LIST | 1 | 18 | 31 (0)| 00:00:01 | ----------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id): ------------------------------------------------------------- 1 - SEL$1 / T@SEL$1 Outline Data ------------- PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS OPTIMIZER_FEATURES_ENABLE('18.1.0') DB_VERSION('18.1.0') ALL_ROWS OUTLINE_LEAF(@"SEL$1") FULL(@"SEL$1" "T"@"SEL$1") END_OUTLINE_DATA */ PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("TABLE_NAME"='ACCESS$') Column Projection Information (identified by operation id): ----------------------------------------------------------- 1 - (rowset=256) "TABLE_NAME"[VARCHAR2,128] Note PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------ ----- - SQL plan baseline SQL_PLAN_7hy1htv240ayzc127edb7 used for this statement 已选择 47 行。 

可以看到此时的执行计划就是刚刚加HINTS的SQL语句的执行计划了。

原文链接:https://my.oschina.net/u/3255159/blog/3039553
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