about histogram(1)
analyze的size 指定histogram的最大buckets,the default value is 75,minimum value is 1,and maximum value is 254.
------------quote begin----<
Column statistics appear in the data dictionary views USER_TAB_COLUMNS, ALL_
TAB_COLUMNS, and DBA_TAB_COLUMNS. Histograms appear in the data dictionary
views USER_TAB_HISTOGRAMS, DBA_TAB_HISTOGRAMS, and ALL_TAB_
HISTOGRAMS; USER_PART_HISTOGRAMS, DBA_PART_HISTOGRAMS, and ALL_
PART_HISTOGRAMS; and USER_SUBPART_HISTOGRAMS, DBA_SUBPART_
HISTOGRAMS, and ALL_SUBPART_HISTOGRAMS.
...........
Oracle Database does not create a histogram with more buckets than the number of
rows in the sample. Also, if the sample contains any values that are very repetitious,
then Oracle Database creates the specified number of buckets, but the value
indicated by the NUM_BUCKETS column of the ALL_, DBA_, and USER_TAB_
COLUMNS views may be smaller because of an internal compression algorithm.
----------------quote end--------------------------------------------
在實際環境中查得資料如下:
#獲取列上的統計資訊
col COLUMN_NAME for a20
col LOW_VALUE for a20
col HIGH_VALUE for a20
set linesize 1000
select COLUMN_NAME,NUM_DISTINCT,LOW_VALUE,HIGH_VALUE,DENSITY,NUM_NULLS,NUM_BUCKETS,LAST_ANALYZED
from user_tab_columns
where table_name='C2CCLASSRELATION'
and LAST_ANALYZED is not null;
COLUMN_NAME NUM_DISTINCT LOW_VALUE HIGH_VALUE DENSITY NUM_NULLS NUM_BUCKETS LAST_ANALYZE
-------------------- ------------ -------------------- -------------------- ---------- ---------- ----------- ------------
FLEAF_CLASSID 4913 C104 C3034A1B .000203542 0 75 04-FEB-07
select SAMPLE_SIZE,AVG_COL_LEN,CHAR_LENGTH,HISTOGRAM
from user_tab_columns
where table_name='C2CCLASSRELATION'
and LAST_ANALYZED is not null;
SAMPLE_SIZE AVG_COL_LEN CHAR_LENGTH HISTOGRAM
----------- ----------- ----------- ---------------
4913 5 0 HEIGHT BALANCED
##查列上histogram詳細資訊
col COLUMN_NAME for a15
col ENDPOINT_NUMBER for 99999999
col ENDPOINT_VALUE for 99999999
col ENDPOINT_ACTUAL_VALUE for a30
set head off
set pagesize 1000 linesize 1000
select COLUMN_NAME,ENDPOINT_NUMBER,ENDPOINT_VALUE,ENDPOINT_ACTUAL_VALUE from dba_tab_histograms where table_name='C2CCLASSRELATION';
FLEAF_CLASSID 0 3
FLEAF_CLASSID 1 72
FLEAF_CLASSID 2 147
FLEAF_CLASSID 3 2052
FLEAF_CLASSID 4 2128
FLEAF_CLASSID 5 3071
FLEAF_CLASSID 6 4043
FLEAF_CLASSID 7 5085
FLEAF_CLASSID 8 6003
FLEAF_CLASSID 9 6077
FLEAF_CLASSID 10 7019
FLEAF_CLASSID 11 7089
FLEAF_CLASSID 12 7160
FLEAF_CLASSID 13 7233
FLEAF_CLASSID 14 8066
FLEAF_CLASSID 15 9019
FLEAF_CLASSID 16 9089
FLEAF_CLASSID 17 9164
FLEAF_CLASSID 18 10061
FLEAF_CLASSID 19 11073
FLEAF_CLASSID 20 12041
FLEAF_CLASSID 21 20013
FLEAF_CLASSID 22 20083
FLEAF_CLASSID 23 20152
FLEAF_CLASSID 24 20529
FLEAF_CLASSID 25 20603
FLEAF_CLASSID 26 21017
FLEAF_CLASSID 27 21529
FLEAF_CLASSID 28 21599
FLEAF_CLASSID 29 22039
FLEAF_CLASSID 30 22115
FLEAF_CLASSID 31 22558
FLEAF_CLASSID 32 22631
FLEAF_CLASSID 33 23053
FLEAF_CLASSID 34 23126
FLEAF_CLASSID 35 23566
FLEAF_CLASSID 36 24003
FLEAF_CLASSID 37 24075
FLEAF_CLASSID 38 24149
FLEAF_CLASSID 39 24549
FLEAF_CLASSID 40 24624
FLEAF_CLASSID 41 24707
FLEAF_CLASSID 42 24816
FLEAF_CLASSID 43 24936
FLEAF_CLASSID 44 25038
FLEAF_CLASSID 45 25130
FLEAF_CLASSID 46 25196
FLEAF_CLASSID 47 25261
FLEAF_CLASSID 48 25347
FLEAF_CLASSID 49 25415
FLEAF_CLASSID 50 25480
FLEAF_CLASSID 51 25545
FLEAF_CLASSID 52 25611
FLEAF_CLASSID 53 25677
FLEAF_CLASSID 54 25743
FLEAF_CLASSID 55 25809
FLEAF_CLASSID 56 25875
FLEAF_CLASSID 57 25943
FLEAF_CLASSID 58 26012
FLEAF_CLASSID 59 26079
FLEAF_CLASSID 60 26144
FLEAF_CLASSID 61 26209
FLEAF_CLASSID 62 26328
FLEAF_CLASSID 63 26393
FLEAF_CLASSID 64 26458
FLEAF_CLASSID 65 26527
FLEAF_CLASSID 66 26594
FLEAF_CLASSID 67 26666
FLEAF_CLASSID 68 26739
FLEAF_CLASSID 69 26819
FLEAF_CLASSID 70 26892
FLEAF_CLASSID 71 26998
FLEAF_CLASSID 72 27071
FLEAF_CLASSID 73 27141
FLEAF_CLASSID 74 27260
FLEAF_CLASSID 75 27326
76 rows selected.
##the following is the command to collect the statistics of 'C2CCLASSRELATION'
EXECUTE DBMS_STATS.gather_table_stats(ownname=>'C2CDB',tabname=>'C2CCLASSRELATION',estimate_percent=>10,method_opt=>'FOR ALL INDEXED COLUMNS',cascade=>true,degree=>8);
所以,dbms_stats的size預設值與analyze一致,另外,如果不指定sample,預設是1(即100%)
yong huang對histogram相關分析文章是
來自 “ ITPUB部落格 ” ,連結:http://blog.itpub.net/94384/viewspace-600298/,如需轉載,請註明出處,否則將追究法律責任。
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