[20181225]12CR2 SQL Plan Directives.txt
--//12C引入SQL PLAN Directives.12cR1版本会造成大量的动态取样,影响性能.许多人把OPTIMIZER_ADAPTIVE_FEATURES设置为false.--//这也是为什么我不主张将XX.1版本使用在生产系统.12CR2做了一些改进,废除了OPTIMIZER_ADAPTIVE_FEATURES参数.使用2个新的--//参数OPTIMIZER_ADAPTIVE_PLANS,OPTIMIZER_ADAPTIVE_STATISTICS,缺省前者true,后者为false.--//通过测试说明问题.1.环境:SCOTT@test01p> @ ver1PORT_STRING VERSION BANNER CON_ID-------------------- ---------- -------------------------------------------------------------------------------- ----------IBMPC/WIN_NT64-9.1.0 12.2.0.1.0 Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production 0SCOTT@test01p> show parameter OPTIMIZER_ADAPTIVENAME TYPE VALUE--------------------------------- ------- ------optimizer_adaptive_plans boolean TRUEoptimizer_adaptive_reporting_only boolean FALSEoptimizer_adaptive_statistics boolean FALSE--//注:没有OPTIMIZER_ADAPTIVE_FEATURES参数,optimizer_adaptive_plans=true,optimizer_adaptive_statistics=false.2.建立测试环境:CREATE TABLE tAS SELECT ROWNUM id ,LPAD ('x', 20, 'x') name ,MOD (ROWNUM, 3) flag1 ,MOD (ROWNUM, 3) flag2 ,MOD (ROWNUM, 3) flag3 FROM DUAL CONNECT BY LEVEL <= 1e5;--//说明:flags1,flags2,flags3分别存在3个取值,按照道理存在27种选择.因为存在相关性,仅仅存在3种选择.3.测试:SCOTT@test01p> alter session set statistics_level=all;Session altered.SCOTT@test01p> select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1;COUNT(DISTINCTNAME)------------------- 1SCOTT@test01p> @ dpc '' ''PLAN_TABLE_OUTPUT-------------------------------------SQL_ID 872fdta99gdk8, child number 0-------------------------------------select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1Plan hash value: 2359337548---------------------------------------------------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | Reads | OMem | 1Mem | Used-Mem |---------------------------------------------------------------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | | | 155 (100)| | 1 |00:00:00.06 | 556 | 540 | | | || 1 | SORT AGGREGATE | | 1 | 1 | 12 | | | 1 |00:00:00.06 | 556 | 540 | | | || 2 | VIEW | VW_DAG_0 | 1 | 1 | 12 | 155 (2)| 00:00:01 | 1 |00:00:00.06 | 556 | 540 | | | || 3 | HASH GROUP BY | | 1 | 1 | 30 | 155 (2)| 00:00:01 | 1 |00:00:00.06 | 556 | 540 | 1345K| 1345K| 504K (0)||* 4 | TABLE ACCESS FULL| T | 1 | 3704 | 108K| 154 (1)| 00:00:01 | 33334 |00:00:00.06 | 556 | 540 | | | |---------------------------------------------------------------------------------------------------------------------------------------------------------------Query Block Name / Object Alias (identified by operation id):------------------------------------------------------------- 1 - SEL$C33C846D 2 - SEL$5771D262 / VW_DAG_0@SEL$C33C846D 3 - SEL$5771D262 4 - SEL$5771D262 / T@SEL$1Predicate Information (identified by operation id):--------------------------------------------------- 4 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))--//注意看id=4, E-Rows=3704,估算按照100000/27 = 3703.7,而A-Rows=33334(10000/3 = 3333.3),存在很大偏差.SCOTT@test01p> select sql_id,child_number,is_reoptimizable from v$sql where sql_id ='872fdta99gdk8';SQL_ID CHILD_NUMBER I------------- ------------ -872fdta99gdk8 0 Y--//is_reoptimizable='Y'SCOTT@test01p> exec dbms_spd.flush_sql_plan_directive;PL/SQL procedure successfully completed.set numw 20column NOTES format a50SELECT directive_id ,TYPE ,enabled ,state ,notes ,reason FROM dba_sql_plan_directives WHERE directive_id IN (SELECT directive_id FROM dba_sql_plan_dir_objects WHERE owner = USER AND object_name = 'T'); DIRECTIVE_ID TYPE ENA STATE NOTES REASON-------------------- -------------------- --- -------------------- -------------------------------------------------- ------------------------------------17342821566768621333 DYNAMIC_SAMPLING YES USABLE <spd_note><internal_state>NEW</internal_state><red SINGLE TABLE CARDINALITY MISESTIMATE undant>NO</redundant><spd_text>{EC(SCOTT.T)[FLAG1, FLAG2, FLAG3]}</spd_text></spd_note>--//指导建议字段flag1,flag2,flag3联合查询时存在偏差,建议动态取样.--//补充说明:{EC(SCOTT.T)[FLAG1,FLAG2, FLAG3]}--//这里的E和C，以及可能出现其他的字符，解释如下：E – equality_predicates_onlyC – simple_column_predicates_onlyJ – index_access_by_join_predicatesF – filter_on_joining_object--//再次执行:SCOTT@test01p> select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1;COUNT(DISTINCTNAME)------------------- 1SCOTT@test01p> @ dpc '' ''PLAN_TABLE_OUTPUT-------------------------------------SQL_ID 872fdta99gdk8, child number 1-------------------------------------select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1Plan hash value: 2359337548------------------------------------------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |------------------------------------------------------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | | | 156 (100)| | 1 |00:00:00.01 | 556 | | | || 1 | SORT AGGREGATE | | 1 | 1 | 12 | | | 1 |00:00:00.01 | 556 | | | || 2 | VIEW | VW_DAG_0 | 1 | 1 | 12 | 156 (2)| 00:00:01 | 1 |00:00:00.01 | 556 | | | || 3 | HASH GROUP BY | | 1 | 1 | 30 | 156 (2)| 00:00:01 | 1 |00:00:00.01 | 556 | 1345K| 1345K| 505K (0)||* 4 | TABLE ACCESS FULL| T | 1 | 33334 | 976K| 154 (1)| 00:00:01 | 33334 |00:00:00.01 | 556 | | | |------------------------------------------------------------------------------------------------------------------------------------------------------Query Block Name / Object Alias (identified by operation id):------------------------------------------------------------- 1 - SEL$C33C846D 2 - SEL$5771D262 / VW_DAG_0@SEL$C33C846D 3 - SEL$5771D262 4 - SEL$5771D262 / T@SEL$1Predicate Information (identified by operation id):--------------------------------------------------- 4 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))Note----- - statistics feedback used for this statement--//注意note,指示statistics feedback used for this statement.SCOTT@test01p> select sql_id,child_number,is_reoptimizable from v$sql where sql_id ='872fdta99gdk8';SQL_ID CHILD_NUMBER I------------- -------------------- -872fdta99gdk8 0 Y872fdta99gdk8 1 NSCOTT@test01p> @ share 872fdta99gdk8SQL_TEXT = select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1SQL_ID = 872fdta99gdk8ADDRESS = 000007FF1393F830CHILD_ADDRESS = 000007FF13D9C198CHILD_NUMBER = 0USE_FEEDBACK_STATS = YREASON = <ChildNode><ChildNumber>0</ChildNumber><ID>48</ID><reason>Auto Reoptimization Mismatch(1)</reason><size>3x4</size><kxscflg>32</kxscflg><kxscfl4>4194560</kxscfl4><dnum_kksfcxe>0</dnum_kksfcxe></ChildNode>--------------------------------------------------SQL_TEXT = select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1SQL_ID = 872fdta99gdk8ADDRESS = 000007FF1393F830CHILD_ADDRESS = 000007FF115A7E58CHILD_NUMBER = 1REASON =--------------------------------------------------PL/SQL procedure successfully completed.SELECT directive_id ,TYPE ,enabled ,state ,notes ,reason FROM dba_sql_plan_directives WHERE directive_id IN (SELECT directive_id FROM dba_sql_plan_dir_objects WHERE owner = USER AND object_name = 'T'); DIRECTIVE_ID TYPE ENA STATE NOTES REASON-------------------- -------------------- --- -------------------- -------------------------------------------------- ------------------------------------17342821566768621333 DYNAMIC_SAMPLING YES USABLE <spd_note><internal_state>NEW</internal_state><red SINGLE TABLE CARDINALITY MISESTIMATE undant>NO</redundant><spd_text>{EC(SCOTT.T)[FLAG1, FLAG2, FLAG3]}</spd_text></spd_note>4.继续测试:--//设置OPTIMIZER_ADAPTIVE_STATISTICS=true看看.SCOTT@test01p> alter session set OPTIMIZER_ADAPTIVE_STATISTICS=true ;Session altered.SCOTT@test01p> select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1;COUNT(DISTINCTNAME)------------------- 1SCOTT@test01p> @ dpc '' ''PLAN_TABLE_OUTPUT-------------------------------------SQL_ID 872fdta99gdk8, child number 2-------------------------------------select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1Plan hash value: 2359337548------------------------------------------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |------------------------------------------------------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | | | 157 (100)| | 1 |00:00:00.01 | 556 | | | || 1 | SORT AGGREGATE | | 1 | 1 | 12 | | | 1 |00:00:00.01 | 556 | | | || 2 | VIEW | VW_DAG_0 | 1 | 1 | 12 | 157 (3)| 00:00:01 | 1 |00:00:00.01 | 556 | | | || 3 | HASH GROUP BY | | 1 | 1 | 30 | 157 (3)| 00:00:01 | 1 |00:00:00.01 | 556 | 1345K| 1345K| 496K (0)||* 4 | TABLE ACCESS FULL| T | 1 | 48497 | 1420K| 154 (1)| 00:00:01 | 33334 |00:00:00.01 | 556 | | | |------------------------------------------------------------------------------------------------------------------------------------------------------Query Block Name / Object Alias (identified by operation id):------------------------------------------------------------- 1 - SEL$C33C846D 2 - SEL$5771D262 / VW_DAG_0@SEL$C33C846D 3 - SEL$5771D262 4 - SEL$5771D262 / T@SEL$1Predicate Information (identified by operation id):--------------------------------------------------- 4 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))Note----- - dynamic statistics used: dynamic sampling (level=2) - 1 Sql Plan Directive used for this statement--//设置OPTIMIZER_ADAPTIVE_STATISTICS=true的情况下,做了动态取样(level=2).产生新的子光标.SCOTT@test01p> select sql_id,child_number,is_reoptimizable from v$sql where sql_id ='872fdta99gdk8';SQL_ID CHILD_NUMBER I------------- -------------------- -872fdta99gdk8 0 Y872fdta99gdk8 1 N872fdta99gdk8 2 NSCOTT@test01p> @ share 872fdta99gdk8old 15: and q.sql_id like ''&1''',new 15: and q.sql_id like ''872fdta99gdk8''',SQL_TEXT = select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1SQL_ID = 872fdta99gdk8ADDRESS = 000007FF1393F830CHILD_ADDRESS = 000007FF13D9C198CHILD_NUMBER = 0USE_FEEDBACK_STATS = YREASON = <ChildNode><ChildNumber>0</ChildNumber><ID>48</ID><reason>Auto Reoptimization Mismatch(1)</reason><size>3x4</size><kxscflg>32</kxscflg><kxscfl4>4194560</kxscfl4><dnum_kksfcxe>0</dnum_kksfcxe></ChildNode>--------------------------------------------------SQL_TEXT = select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1SQL_ID = 872fdta99gdk8ADDRESS = 000007FF1393F830CHILD_ADDRESS = 000007FF115A7E58CHILD_NUMBER = 1REASON = <ChildNode><ChildNumber>1</ChildNumber><ID>3</ID><reason>Optimizer mismatch(12)</reason><size>2x440</size><_optimizer_dsdir_usage_control> 0 126 </_optimizer_dsdir_usage_control><optimizer_adaptive_statistics> falsetrue </optimizer_adaptive_statistics><_optimizer_use_feedback_for_join> false true </_optimizer_use_feedback_for_join><_optimizer_ads_for_pq> false true </_optimizer_ads_for_pq></ChildNode>--------------------------------------------------SQL_TEXT = select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1SQL_ID = 872fdta99gdk8ADDRESS = 000007FF1393F830CHILD_ADDRESS = 000007FF0FDBE618CHILD_NUMBER = 2OPTIMIZER_MISMATCH = YREASON =--------------------------------------------------SCOTT@test01p> exec dbms_spd.flush_sql_plan_directive;PL/SQL procedure successfully completed.SELECT directive_id ,TYPE ,enabled ,state ,notes ,reason FROM dba_sql_plan_directives WHERE directive_id IN (SELECT directive_id FROM dba_sql_plan_dir_objects WHERE owner = USER AND object_name = 'T'); DIRECTIVE_ID TYPE ENA STATE NOTES REASON-------------------- -------------------- --- ------ -------------------------------------------------- ------------------------------------14350253949522184195 DYNAMIC_SAMPLING_RES YES USABLE <spd_note><internal_state>NEW</internal_state><red VERIFY CARDINALITY ESTIMATE ULT undant>NO</redundant><spd_text>{(SCOTT.T, num_rows =100000) - (SQL_ID:4k5yrxfcvd5qb, T.CARD=48497[-2 -2])}</spd_text></spd_note>17342821566768621333 DYNAMIC_SAMPLING YES USABLE <spd_note><internal_state>MISSING_STATS</internal_ SINGLE TABLE CARDINALITY MISESTIMATE state><redundant>NO</redundant><spd_text>{EC(SCOTT .T)[FLAG1, FLAG2, FLAG3]}</spd_text></spd_note>--//多了一行,动态取样分析后估计T.CARD=48497,虽然与实际A-Rows=33334还是存在很大偏差.指导提示是MISSING_STATS.--//补充说明SQL_ID:4k5yrxfcvd5qb,我没有查询到对于sql语句,有点奇怪!!SCOTT@test01p> exec dbms_stats.gather_table_stats(user,'T',options=>'gather auto',no_invalidate=>false);PL/SQL procedure successfully completed.SCOTT@test01p> select column_name,num_buckets,histogram from user_tab_col_statistics where table_name ='T';COLUMN_NAME NUM_BUCKETS HISTOGRAM----------- ----------- ---------------ID 1 NONENAME 1 NONEFLAG1 3 FREQUENCYFLAG2 3 FREQUENCYFLAG3 3 FREQUENCY--//并没有指导建议生成相关列的统计信息.--//实际上12cR2引入新参数AUTO_STAT_EXTENSIONS控制extended stats的收集,缺省设置off.(没有打开).设置AUTO_STAT_EXTENSIONS=on可以打开.SCOTT@test01p> select dbms_stats.get_prefs('AUTO_STAT_EXTENSIONS') c10 from dual;C10----------OFFSCOTT@test01p> exec dbms_stats.set_global_prefs('AUTO_STAT_EXTENSIONS','ON') ;PL/SQL procedure successfully completed.SCOTT@test01p> select dbms_stats.get_prefs('AUTO_STAT_EXTENSIONS') c10 from dual;C10----------ONSCOTT@test01p> exec dbms_stats.gather_table_stats(user,'T',options=>'gather auto',no_invalidate=>false);PL/SQL procedure successfully completed.SCOTT@test01p> column COLUMN_NAME format a30SCOTT@test01p> select column_name,num_buckets,histogram from user_tab_col_statistics where table_name ='T';COLUMN_NAME NUM_BUCKETS HISTOGRAM------------------------------ ----------- ---------------ID 1 NONENAME 1 NONEFLAG1 3 FREQUENCYFLAG2 3 FREQUENCYFLAG3 3 FREQUENCYSYS_STS0SR$HPC$E#KVDPEN#0R2JOU 3 FREQUENCY6 rows selected.SCOTT@test01p> column EXTENSION_name format a30SCOTT@test01p> select * from user_stat_extensions where table_name ='T';TABLE_NAME EXTENSION_NAME EXTENSION CREATOR DRO---------- ------------------------------ ------------------------- ------- ---T SYS_STS0SR$HPC$E#KVDPEN#0R2JOU ("FLAG1","FLAG2","FLAG3") SYSTEM YES--//可以发现现在收集了相关列("FLAG1","FLAG2","FLAG3")的统计,并且建立了直方图.SCOTT@test01p> alter session set OPTIMIZER_ADAPTIVE_STATISTICS=false ;Session altered.SCOTT@test01p> select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1;COUNT(DISTINCTNAME)------------------- 1SCOTT@test01p> @ dpc '' ''PLAN_TABLE_OUTPUT-------------------------------------SQL_ID 872fdta99gdk8, child number 1-------------------------------------select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1Plan hash value: 2359337548------------------------------------------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |------------------------------------------------------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | | | 156 (100)| | 1 |00:00:00.01 | 556 | | | || 1 | SORT AGGREGATE | | 1 | 1 | 12 | | | 1 |00:00:00.01 | 556 | | | || 2 | VIEW | VW_DAG_0 | 1 | 1 | 12 | 156 (2)| 00:00:01 | 1 |00:00:00.01 | 556 | | | || 3 | HASH GROUP BY | | 1 | 1 | 30 | 156 (2)| 00:00:01 | 1 |00:00:00.01 | 556 | 1345K| 1345K| 507K (0)||* 4 | TABLE ACCESS FULL| T | 1 | 33334 | 976K| 154 (1)| 00:00:01 | 33334 |00:00:00.01 | 556 | | | |------------------------------------------------------------------------------------------------------------------------------------------------------Query Block Name / Object Alias (identified by operation id):------------------------------------------------------------- 1 - SEL$C33C846D 2 - SEL$5771D262 / VW_DAG_0@SEL$C33C846D 3 - SEL$5771D262 4 - SEL$5771D262 / T@SEL$1Predicate Information (identified by operation id):--------------------------------------------------- 4 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))--//可以发现E-Rows已经正确修正.SCOTT@test01p> exec dbms_spd.flush_sql_plan_directive;PL/SQL procedure successfully completed. DIRECTIVE_ID TYPE ENA STATE NOTES REASON-------------------- -------------------- --- -------------------- -------------------------------------------------- ------------------------------------14350253949522184195 DYNAMIC_SAMPLING_RES YES USABLE <spd_note><internal_state>NEW</internal_state><red VERIFY CARDINALITY ESTIMATE ULT undant>NO</redundant><spd_text>{(SCOTT.T, num_rows =100000) - (SQL_ID:4k5yrxfcvd5qb, T.CARD=48497[-2 -2])}</spd_text></spd_note>17342821566768621333 DYNAMIC_SAMPLING YES SUPERSEDED <spd_note><internal_state>HAS_STATS</internal_stat SINGLE TABLE CARDINALITY MISESTIMATE e><redundant>NO</redundant><spd_text>{EC(SCOTT.T)[ FLAG1, FLAG2, FLAG3]}</spd_text></spd_note>--//注意看现在不是MISSING_STATS而是提示HAS_STATS. SUPERSEDED 表示 取代，接替.--//有了相关列统计其它涉及相关列的查询就不会在动态取样,而是估计行数与实际行数接近.而且执行其它类似语句也不会出现is_reoptimizable='Y'的情况.SCOTT@test01p> select max(id) from t where flag1=1 and flag2=1 and flag3=1; MAX(ID)---------- 100000SCOTT@test01p> @ dpc '' ''PLAN_TABLE_OUTPUT-------------------------------------SQL_ID 6stmvx0gcybbg, child number 0-------------------------------------select max(id) from t where flag1=1 and flag2=1 and flag3=1Plan hash value: 2966233522---------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers |---------------------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | | | 154 (100)| | 1 |00:00:00.01 | 556 || 1 | SORT AGGREGATE | | 1 | 1 | 14 | | | 1 |00:00:00.01 | 556 ||* 2 | TABLE ACCESS FULL| T | 1 | 33334 | 455K| 154 (1)| 00:00:01 | 33334 |00:00:00.01 | 556 |---------------------------------------------------------------------------------------------------------------------Query Block Name / Object Alias (identified by operation id):------------------------------------------------------------- 1 - SEL$1 2 - SEL$1 / T@SEL$1Predicate Information (identified by operation id):--------------------------------------------------- 2 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))SCOTT@test01p> select sql_id,child_number,is_reoptimizable from v$sql where sql_id ='6stmvx0gcybbg';SQL_ID CHILD_NUMBER I------------- ------------ -6stmvx0gcybbg 0 N--//is_reoptimizable = 'N'.总结:--//12cR2做了一些改进,optimizer_adaptive_statistics=false,避免大量的动态取样对性能的影响.另外即使设置optimizer_adaptive_statistics=true.--//oracle也保存了动态取样的结果.--//dbms_stats引入新的参数AUTO_STAT_EXTENSIONS,缺省是off.设置on后再分析自动建立扩展统计信息.