[20181225]12CR2 SQL Plan Directives.txt
[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> @ ver1
PORT_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 0
SCOTT@test01p> show parameter OPTIMIZER_ADAPTIVE
NAME TYPE VALUE
--------------------------------- ------- ------
optimizer_adaptive_plans boolean TRUE
optimizer_adaptive_reporting_only boolean FALSE
optimizer_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 t
AS
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)
-------------------
1
SCOTT@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=1
Plan 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$1
Predicate Information (identified by operation id):
---------------------------------------------------
4 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))
--//注意看id=4, E-Rows=3704,估算按照100000/27 = 3703.7,而A-Rows=33334(10000/3 = 3333.3),存在很大偏差.
SCOTT@test01p> select sql_id,child_number,is_reoptimizable from v$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 20
column NOTES format a50
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>
--//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_only
C – simple_column_predicates_only
J – index_access_by_join_predicates
F – 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)
-------------------
1
SCOTT@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=1
Plan 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$1
Predicate Information (identified by operation id):
---------------------------------------------------
4 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))
Note
-----
- statistics feedback used for this statement
--//注意note,指示statistics feedback used for this statement.
SCOTT@test01p> select sql_id,child_number,is_reoptimizable from v$sql where sql_id ='872fdta99gdk8';
SQL_ID CHILD_NUMBER I
------------- -------------------- -
872fdta99gdk8 0 Y
872fdta99gdk8 1 N
SCOTT@test01p> @ share 872fdta99gdk8
SQL_TEXT = select count(distinct name) from t where flag1=1 and flag2=1 and flag3=1
SQL_ID = 872fdta99gdk8
ADDRESS = 000007FF1393F830
CHILD_ADDRESS = 000007FF13D9C198
CHILD_NUMBER = 0
USE_FEEDBACK_STATS = Y
REASON = <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=1
SQL_ID = 872fdta99gdk8
ADDRESS = 000007FF1393F830
CHILD_ADDRESS = 000007FF115A7E58
CHILD_NUMBER = 1
REASON =
--------------------------------------------------
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)
-------------------
1
SCOTT@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=1
Plan 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$1
Predicate Information (identified by operation id):
---------------------------------------------------
4 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))
Note
-----
- dynamic statistics used: dynamic sampling (level=2)
- 1 Sql Plan Directive used for this statement
--//设置OPTIMIZER_ADAPTIVE_STATISTICS=true的情况下,做了动态取样(level=2).产生新的子光标.
SCOTT@test01p> select sql_id,child_number,is_reoptimizable from v$sql where sql_id ='872fdta99gdk8';
SQL_ID CHILD_NUMBER I
------------- -------------------- -
872fdta99gdk8 0 Y
872fdta99gdk8 1 N
872fdta99gdk8 2 N
SCOTT@test01p> @ share 872fdta99gdk8
old 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=1
SQL_ID = 872fdta99gdk8
ADDRESS = 000007FF1393F830
CHILD_ADDRESS = 000007FF13D9C198
CHILD_NUMBER = 0
USE_FEEDBACK_STATS = Y
REASON = <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=1
SQL_ID = 872fdta99gdk8
ADDRESS = 000007FF1393F830
CHILD_ADDRESS = 000007FF115A7E58
CHILD_NUMBER = 1
REASON = <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_stat
istics> false
true </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=1
SQL_ID = 872fdta99gdk8
ADDRESS = 000007FF1393F830
CHILD_ADDRESS = 000007FF0FDBE618
CHILD_NUMBER = 2
OPTIMIZER_MISMATCH = Y
REASON =
--------------------------------------------------
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 NONE
NAME 1 NONE
FLAG1 3 FREQUENCY
FLAG2 3 FREQUENCY
FLAG3 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
----------
OFF
SCOTT@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
----------
ON
SCOTT@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 a30
SCOTT@test01p> select column_name,num_buckets,histogram from user_tab_col_statistics where table_name ='T';
COLUMN_NAME NUM_BUCKETS HISTOGRAM
------------------------------ ----------- ---------------
ID 1 NONE
NAME 1 NONE
FLAG1 3 FREQUENCY
FLAG2 3 FREQUENCY
FLAG3 3 FREQUENCY
SYS_STS0SR$HPC$E#KVDPEN#0R2JOU 3 FREQUENCY
6 rows selected.
SCOTT@test01p> column EXTENSION_name format a30
SCOTT@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)
-------------------
1
SCOTT@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=1
Plan 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$1
Predicate 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)
----------
100000
SCOTT@test01p> @ dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID 6stmvx0gcybbg, child number 0
-------------------------------------
select max(id) from t where flag1=1 and flag2=1 and flag3=1
Plan 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$1
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter(("FLAG1"=1 AND "FLAG2"=1 AND "FLAG3"=1))
SCOTT@test01p> select sql_id,child_number,is_reoptimizable from v$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.
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