[20170612]FOR ALL COLUMNS SIZE repeat(12c).txt
–//今日看了https://jonathanlewis.wordpress.com/2017/06/01/histogram-upgrade-2/,提到了直方图的问题,
–//越发是FOR ALL COLUMNS SIZE repeat引起的标题,在有些非正规情状要注意.
1.环境:
SCOTT@test01p> @ ver1
PORT_STRING VERSION
BANNER
CON_ID
IBMPC/WIN_NT64-9.1.0 12.1.0.1.0 Oracle Database 12c
Enterprise Edition Release 12.1.0.1.0 – 64bit Production 0
create table t (id number,pad varchar2(20),flag varchar2(1));
insert into t select rownum,lpad(‘a’,20,’a’) ,’a’ from dual connect by
level<=2e4;
insert into t select rownum+2e4,lpad(‘d’,20,’d’) ,’d’ from dual connect
by level<=2;
commit ;
SCOTT@test01p> exec dbms_stats.Gather_table_stats(ownname =>
user, tabname => ‘T’,method_opt => ‘FOR ALL COLUMNS ‘);
PL/SQL procedure successfully completed.
SCOTT@test01p> SELECT flag, COUNT(*) FROM t GROUP BY flag;
F COUNT(*)
d 2
a 20000
select * from DBA_TAB_COL_STATISTICS where owner=user and
table_name=’T’ and column_name=’FLAG’;
Record View
As of: 2017/6/12 20:38:56
OWNER: SCOTT
TABLE_NAME: T
COLUMN_NAME: FLAG
NUM_DISTINCT: 2
LOW_VALUE: 61
HIGH_VALUE: 64
DENSITY: 0.000024997500249975
NUM_NULLS: 0
NUM_BUCKETS: 2
LAST_ANALYZED: 2017/6/12 20:37:55
SAMPLE_SIZE: 20002
GLOBAL_STATS: YES
USER_STATS: NO
NOTES:
AVG_COL_LEN: 2
HISTOGRAM: FREQUENCY
SCOPE: SHARED
–//建立了直方图.bucket=2.
SCOTT@test01p> set numw 36
SCOTT@test01p> select * from USER_TAB_HISTOGRAMS where
column_name=’FLAG’;
TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER
ENDPOINT_VALUE ENDPOINT_A ENDPOINT_ACTUAL_VALU
ENDPOINT_REPEAT_COUNT SCOPE
T FLAG 20000
503652795277878000000000000000000000
0 SHARED
T FLAG 20002
519229685853483000000000000000000000
0 SHARED
–//借使应用形式暴发变化,参加了2种值.
insert into t select rownum+2e4+2,lpad(‘b’,20,’b’) ,’b’ from dual
connect by level<=2e4;
insert into t select rownum+4e4+2,lpad(‘c’,20,’c’) ,’c’ from dual
connect by level<=2;
commit ;
SCOTT@test01p> exec dbms_stats.Gather_table_stats(ownname =>
user, tabname => ‘T’,method_opt => ‘FOR ALL COLUMNS size
repeat’,No_Invalidate => false);
PL/SQL procedure successfully completed.
–//加入No_Invalidate =>
false,首要使实践布署能马上使用新的总计音信.
select * from DBA_TAB_COL_STATISTICS where owner=user and
table_name=’T’ and column_name=’FLAG’;
Record View
As of: 2017/6/12 20:42:29
OWNER: SCOTT
TABLE_NAME: T
COLUMN_NAME: FLAG
NUM_DISTINCT: 4
LOW_VALUE: 61
HIGH_VALUE: 64
DENSITY: 0.25
NUM_NULLS: 0
NUM_BUCKETS: 2
LAST_ANALYZED: 2017/6/12 20:42:01
SAMPLE_SIZE: 5463
GLOBAL_STATS: YES
USER_STATS: NO
NOTES:
AVG_COL_LEN: 2
HISTOGRAM: HYBRID
SCOPE: SHARED
–//因为bucket桶没有成形,直方图变成了HYBRID.
SCOTT@test01p> select * from USER_TAB_HISTOGRAMS where
table_name=’T’ and column_name=’FLAG’;
TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER
ENDPOINT_VALUE ENDPOINT_A ENDPOINT_ACTUAL_VALU
ENDPOINT_REPEAT_COUNT SCOPE
T FLAG 2760
503652795277878000000000000000000000
2760 SHARED
T FLAG 5463
519229685853483000000000000000000000
1 SHARED
SCOTT@test01p> alter session set statistics_level=all;
Session altered.
SCOTT@test01p> SELECT flag, COUNT(*) FROM t GROUP BY flag order by
1;
F COUNT(*)
a 20000
b 20000
c 2
d 2
SCOTT@test01p> select * from t where flag=’c’;
ID PAD F
40003 cccccccccccccccccccc c
40004 cccccccccccccccccccc c
SCOTT@test01p> @ dpc ” ”
PLAN_TABLE_OUTPUT
SQL_ID g3pmd0h5vnw5r, child number 0
select * from t where flag=’c’
Plan hash value: 1601196873
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost
(%CPU)| E-Time | A-Rows | A-Time | Buffers |
| 0 | SELECT STATEMENT | | 1 | | | 68
(100)| | 2 |00:00:00.01 | 205 |
|* 1 | TABLE ACCESS FULL| T | 1 | 6598 | 180K| 68
(0)| 00:00:01 | 2 |00:00:00.01 | 205 |
Query Block Name / Object Alias (identified by operation id):
1 – SEL$1 / T@SEL$1
Predicate Information (identified by operation id):
1 – filter(“FLAG”=’c’)
23 rows selected.
–//可以发现E-rows 与 A-rows
存在很大的出入,正是业务格局暴发了转移,导致method_opt => ‘FOR ALL
COLUMNS size repeat’存在难题.
–//而这几个难点在11G是不设有的,在利用method_opt => ‘FOR ALL COLUMNS
size repeat’,会增加bucket的数量.
–//如果应用不存在那样的题材,臆想涉及不大.
–//不难的使用如下命令可以规定,”可能”有难点的直方图.
SELECT *
FROM DBA_TAB_COL_STATISTICS
WHERE owner = USER
AND table_name = ‘T’
AND num_distinct < 255
AND histogram NOT LIKE ‘%FREQUENCY%’;
Record View
As of: 2017/6/12 20:46:36
OWNER: SCOTT
TABLE_NAME: T
COLUMN_NAME: FLAG
NUM_DISTINCT: 4
LOW_VALUE: 61
HIGH_VALUE: 64
DENSITY: 0.25
NUM_NULLS: 0
NUM_BUCKETS: 2
LAST_ANALYZED: 2017/6/12 20:42:01
SAMPLE_SIZE: 5463
GLOBAL_STATS: YES
USER_ACCESS，STATS: NO
NOTES:
AVG_COL_LEN: 2
HISTOGRAM: HYBRID
SCOPE: SHARED
–//如若不指定repeat.
SCOTT@test01p> exec dbms_stats.Gather_table_stats(ownname =>
user, tabname => ‘T’,method_opt => ‘FOR ALL COLUMNS
‘,No_Invalidate => false);
PL/SQL procedure successfully completed.
SCOTT@test01p> select * from USER_TAB_HISTOGRAMS where
table_name=’T’ and column_name=’FLAG’;
TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER
ENDPOINT_VALUE ENDPOINT_A ENDPOINT_ACTUAL_VALU
ENDPOINT_REPEAT_COUNT SCOPE
T FLAG 20000
503652795277878000000000000000000000
0 SHARED
T FLAG 40000
508845092136413000000000000000000000
0 SHARED
T FLAG 40002
514037388994948000000000000000000000
0 SHARED
T FLAG 40004
519229685853483000000000000000000000
0 SHARED
–//分析使用No_Invalidate => false,那样重复履行会再度分析.
select * from DBA_TAB_COL_STATISTICS where owner=user and
table_name=’T’ and column_name=’FLAG’;
Record View
As of: 2017/6/12 20:49:27
OWNER: SCOTT
TABLE_NAME: T
COLUMN_NAME: FLAG
NUM_DISTINCT: 4
LOW_VALUE: 61
HIGH_VALUE: 64
DENSITY: 0.0000124987501249875
NUM_NULLS: 0
NUM_BUCKETS: 4
LAST_ANALYZED: 2017/6/12 20:47:21
SAMPLE_SIZE: 40004
GLOBAL_STATS: YES
USER_STATS: NO
NOTES:
AVG_COL_LEN: 2
HISTOGRAM: FREQUENCY
SCOPE: SHARED
–//那样建立的直方图=FREQUENCY.
SCOTT@test01p> select * from t where flag=’c’;
ID PAD F
40003 cccccccccccccccccccc c
40004 cccccccccccccccccccc c
SCOTT@test01p> @ dpc ” ”
PLAN_TABLE_OUTPUT
SQL_ID g3pmd0h5vnw5r, child number 0
select * from t where flag=’c’
Plan hash value: 1601196873
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost
(%CPU)| E-Time | A-Rows | A-Time | Buffers |
| 0 | SELECT STATEMENT | | 1 | | | 68
(100)| | 2 |00:00:00.01 | 205 |
|* 1 | TABLE ACCESS FULL| T | 1 | 2 | 56 | 68
(0)| 00:00:01 | 2 |00:00:00.01 | 205 |
Query Block Name / Object Alias (identified by operation id):
1 – SEL$1 / T@SEL$1
Predicate Information (identified by operation id):
1 – filter(“FLAG”=’c’)
–//这样就ok了.
–//对于如此的情状最佳的章程手工安装分析方法
BEGIN
dbms_stats.Set_table_prefs(user, ‘T’, ‘METHOD_OPT’=>’FOR ALL
COLUMNS SIZE 1, FOR COLUMNS SIZE AUTO flag’);
END;
/
–//幸免那些题材. 总而言之12c要留意分析方法METHOD_OPT’=>’FOR ALL COLUMNS
SIZE repeat’带来的难点.
–//更加是有的用到格局暴发变化的意况.而11g前边的测试不设有那一个题材.