一、什么是统计信息

oracle数据库里的统计信息是如下的一组数据:他们存储在数据字典里,且从多个维度描述了oracle数据库数据对象的详细信息。

oracle数据库里的统计信息主要分为以下6种情况:

(1)表的统计信息。

(2)列的统计信息。

(3)索引的统计信息。

(4)系统统计信息。

(5)数据字典统计信息。

(6)内部对象统计信息。

二、oracle收集和查看统计信息的方法

oracle数据库收集统计信息一般有以下2种方法:

(1)analyze命令。

(2)dbms_stats包。

针对以上6种统计信息,其中“表的统计信息”,“索引统计信息”,“列统计信息”,“数据字典统计信息”使用analyze或dbms_stats包收集均可以,但是“系统统计信息”和“内部对象统计信息”必须要dbms_stats包来收集才可以。

1、使用analyze命令收集统计信息

从oralce7开始,analyze命令就用来收集表、索引和列的统计信息。从oracle10g开始,创建索引后oracle会自动为您收集目标索引统计信息。analyze命令收集统计信息不会抹掉之间analyze结果。

创建测试表:

SQL>create table t1 as select * from dba_objects;

SQL>create index idx_t1 on t1(object_id);

(1)analyze索引统计信息:

SQL>analyze index idx_t1 delete statistics;

(2)对表收集统计信息,并且以估算模式,采样比为15%:

SQL>analyze table t1 estimate statistics sample 15 percent for table;

(3)对表收集统计信息,以统计模式:

SQL>analyze table t1 compute statistics for table;

(4)对列收集统计信息,以计算模式:

SQL>analyze table t1 compute statistics for columns object_name,object_id;

(5)以计算模式对表和列同时收集统计信息:

SQL>analyze table t1 compute statistics for t1 for columns object_name,object_id;

(6)以计算模式对索引收集统计信息:

SQL>analyze index idx_t1 compute statistics;

(7)删除表、表上的索引、表的所有列的统计信息:

SQL>analyze table t1 delete statistics;

(8)以计算模式,同时收集表、表上的列、表上的索引的统计信息:

SQL>analyze table t1 compute statistics;

2、使用dbms_stats包收集统计信息

从oracle 8.1.5开始,dbms_stats包就被广泛用于统计信息的收集,用dbms_stats包收集统计信息也是oracle官方推荐的方式。在收集CBO所需要的统计信息方面,可以简单的将dbms_stats包理解成是analyze命令的增强版。

DBMS_STATS包最常见的4个存储过程:

(1)dbms_stats.gather_table_stats:用于收集目标表,目标表上列及目标表上索引的统计信息。

(2)dbms_stats.gather_index_stats:用于收集指定索引的统计信息。

(3)dbms_stats.gather_schema_stats:用于收集schema下所有对象的统计信息。

(4)dbms_stats.gather_database_stats:用于收集全库统计对象的统计信息。

以下是dbms_stats包的具体用法:

(1)对表收集统计信息,并且以估算模式,采样比为15%:

SQL>exec dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'T1',estimate_percent=>15,method_opt=>'FOR TABLE',cascade=>FALSE);

注意:method_opt参数指定了FOR TABLE不是在所有版本oracle下都是好用的。

(2)对表收集统计信息,以计算模式:

SQL>exec dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'T1',estimate_percent=>100,method_opt=>'FOR TABLE',cascade=>FALSE);

SQL>exec dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'T1',estimate_percent=>NULL,method_opt=>'FOR TABLE',cascade=>FALSE);

(3)对列收集统计信息,以计算模式:

SQL>exec dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'T1',estimate_percent=>100,method_opt=>'FOR ALL CULUMNS SIZE 1 OBJECT_NAME OBJECT_ID',cascade=>FALSE);

注意:以上方法收集了列objec_name、object_id的统计信息,同时也会收集表的统计信息。

(4)以计算模式对索引收集统计信息:

SQL>exec dbms_stats.gather_index_stats(ownname=>'SCOTT',indname=>'INDEX_T1',estimate_percent=>100);

(5)删除表、表上的索引、表的所有列的统计信息:

SQL>exec dbms_stats.delete_table_stats(ownname=>'SCOTT',tabname=>'T1');

(6)以计算模式,同时收集表、表上的列、表上的索引的统计信息:

SQL>exec dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'T1',estimate_percent=>15 ,cascade=>TRUE);

3、analyze和dbms_stats的区别

(1)analyze命令不能正确的收集分区表的统计信息,而dbms_stats包缺可以。

(2)analyze命令不能以并行收集统计信息,而dbms_stats包缺可以。

SQL>exec dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'T1',estimate_percent=>100, cascade=>FALSE,degree=>4);

(3)dbms_stats包只能收集与CBO相关的统计信息,而与CBO无关的额外信息,比如行迁移/行链接的数量(chain_cnt),校验表和索引的结构信息等,dbms_stats包就无能为力了,而analyze命令是可以用来分析和收集上述额外信息。比如:

SQL>analyze table XXX list chained rows into YYY; --用来分析和收集行迁移/行链接的数量。

SQL>analyze index XXX validate structure;      --用来分析索引结构。

4、查看统计信息

oracle里的统计信息存储在数据字典表中,可以通过脚本来查询对象的统计信息。

sosi.sh脚本如下(可以查看表、索引、列的统计信息):

set echo off

set scan on

set lines 150

set pages 66

set verify off

set feedback off

set termout off

column uservar new_value Table_Owner noprint

select user uservar from dual;

set termout on

column TABLE_NAME heading "Tables owned by &Table_Owner" format a30

select table_name from dba_tables where owner=upper('&Table_Owner') order by 1

/

undefine table_name

undefine owner

prompt

accept owner prompt 'Please enter Name of Table Owner (Null = &Table_Owner): '

accept table_name  prompt 'Please enter Table Name to show Statistics for: '

column TABLE_NAME heading "Table|Name" format a15

column PARTITION_NAME heading "Partition|Name" format a15

column SUBPARTITION_NAME heading "SubPartition|Name" format a15

column NUM_ROWS heading "Number|of Rows" format 9,999,999,990

column BLOCKS heading "Blocks" format 999,990

column EMPTY_BLOCKS heading "Empty|Blocks" format 999,999,990

column AVG_SPACE heading "Average|Space" format 9,990

column CHAIN_CNT heading "Chain|Count" format 999,990

column AVG_ROW_LEN heading "Average|Row Len" format 990

column COLUMN_NAME  heading "Column|Name" format a25

column NULLABLE heading Null|able format a4

column NUM_DISTINCT heading "Distinct|Values" format 999,999,990

column NUM_NULLS heading "Number|Nulls" format 9,999,990

column NUM_BUCKETS heading "Number|Buckets" format 990

column DENSITY heading "Density" format 990

column INDEX_NAME heading "Index|Name" format a15

column UNIQUENESS heading "Unique" format a9

column BLEV heading "B|Tree|Level" format 90

column LEAF_BLOCKS heading "Leaf|Blks" format 990

column DISTINCT_KEYS heading "Distinct|Keys" format 9,999,999,990

column AVG_LEAF_BLOCKS_PER_KEY heading "Average|Leaf Blocks|Per Key" format 99,990

column AVG_DATA_BLOCKS_PER_KEY heading "Average|Data Blocks|Per Key" format 99,990

column CLUSTERING_FACTOR heading "Cluster|Factor" format 999,999,990

column COLUMN_POSITION heading "Col|Pos" format 990

column col heading "Column|Details" format a24

column COLUMN_LENGTH heading "Col|Len" format 9,990

column GLOBAL_STATS heading "Global|Stats" format a6

column USER_STATS heading "User|Stats" format a6

column SAMPLE_SIZE heading "Sample|Size" format 9,999,999,990

column to_char(t.last_analyzed,'MM-DD-YYYY') heading "Date|MM-DD-YYYY" format a10

prompt

prompt ***********

prompt Table Level

prompt ***********

prompt

select

    TABLE_NAME,

    NUM_ROWS,

    BLOCKS,

    EMPTY_BLOCKS,

    AVG_SPACE,

    CHAIN_CNT,

    AVG_ROW_LEN,

    GLOBAL_STATS,

    USER_STATS,

    SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from dba_tables t

where

    owner = upper(nvl('&&Owner',user))

and table_name = upper('&&Table_name')

/

select

    COLUMN_NAME,

    decode(t.DATA_TYPE,

           'NUMBER',t.DATA_TYPE||'('||

           decode(t.DATA_PRECISION,

                  null,t.DATA_LENGTH||')',

                  t.DATA_PRECISION||','||t.DATA_SCALE||')'),

                  'DATE',t.DATA_TYPE,

                  'LONG',t.DATA_TYPE,

                  'LONG RAW',t.DATA_TYPE,

                  'ROWID',t.DATA_TYPE,

                  'MLSLABEL',t.DATA_TYPE,

                  t.DATA_TYPE||'('||t.DATA_LENGTH||')') ||' '||

    decode(t.nullable,

              'N','NOT NULL',

              'n','NOT NULL',

              NULL) col,

    NUM_DISTINCT,

    DENSITY,

    NUM_BUCKETS,

    NUM_NULLS,

    GLOBAL_STATS,

    USER_STATS,

    SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from dba_tab_columns t

where

    table_name = upper('&Table_name')

and owner = upper(nvl('&Owner',user))

/

select

    INDEX_NAME,

    UNIQUENESS,

    BLEVEL BLev,

    LEAF_BLOCKS,

    DISTINCT_KEYS,

    NUM_ROWS,

    AVG_LEAF_BLOCKS_PER_KEY,

    AVG_DATA_BLOCKS_PER_KEY,

    CLUSTERING_FACTOR,

    GLOBAL_STATS,

    USER_STATS,

    SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from

    dba_indexes t

where

    table_name = upper('&Table_name')

and table_owner = upper(nvl('&Owner',user))

/

break on index_name

select

    i.INDEX_NAME,

    i.COLUMN_NAME,

    i.COLUMN_POSITION,

    decode(t.DATA_TYPE,

           'NUMBER',t.DATA_TYPE||'('||

           decode(t.DATA_PRECISION,

                  null,t.DATA_LENGTH||')',

                  t.DATA_PRECISION||','||t.DATA_SCALE||')'),

                  'DATE',t.DATA_TYPE,

                  'LONG',t.DATA_TYPE,

                  'LONG RAW',t.DATA_TYPE,

                  'ROWID',t.DATA_TYPE,

                  'MLSLABEL',t.DATA_TYPE,

                  t.DATA_TYPE||'('||t.DATA_LENGTH||')') ||' '||

           decode(t.nullable,

                  'N','NOT NULL',

                  'n','NOT NULL',

                  NULL) col

from

    dba_ind_columns i,

    dba_tab_columns t

where

    i.table_name = upper('&Table_name')

and owner = upper(nvl('&Owner',user))

and i.table_name = t.table_name

and i.column_name = t.column_name

order by index_name,column_position

/

prompt

prompt ***************

prompt Partition Level

prompt ***************

select

    PARTITION_NAME,

    NUM_ROWS,

    BLOCKS,

    EMPTY_BLOCKS,

    AVG_SPACE,

    CHAIN_CNT,

    AVG_ROW_LEN,

    GLOBAL_STATS,

    USER_STATS,

    SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from

    dba_tab_partitions t

where

    table_owner = upper(nvl('&&Owner',user))

and table_name = upper('&&Table_name')

order by partition_position

/

break on partition_name

select

    PARTITION_NAME,

    COLUMN_NAME,

    NUM_DISTINCT,

    DENSITY,

    NUM_BUCKETS,

    NUM_NULLS,

    GLOBAL_STATS,

    USER_STATS,

    SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from

    dba_PART_COL_STATISTICS t

where

    table_name = upper('&Table_name')

and owner = upper(nvl('&Owner',user))

/

break on partition_name

select

    t.INDEX_NAME,

    t.PARTITION_NAME,

    t.BLEVEL BLev,

    t.LEAF_BLOCKS,

    t.DISTINCT_KEYS,

    t.NUM_ROWS,

    t.AVG_LEAF_BLOCKS_PER_KEY,

    t.AVG_DATA_BLOCKS_PER_KEY,

    t.CLUSTERING_FACTOR,

    t.GLOBAL_STATS,

    t.USER_STATS,

    t.SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from

    dba_ind_partitions t,

    dba_indexes i

where

    i.table_name = upper('&Table_name')

and i.table_owner = upper(nvl('&Owner',user))

and i.owner = t.index_owner

and i.index_name=t.index_name

/

prompt

prompt ***************

prompt SubPartition Level

prompt ***************

select

    PARTITION_NAME,

    SUBPARTITION_NAME,

    NUM_ROWS,

    BLOCKS,

    EMPTY_BLOCKS,

    AVG_SPACE,

    CHAIN_CNT,

    AVG_ROW_LEN,

    GLOBAL_STATS,

    USER_STATS,

    SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from

    dba_tab_subpartitions t

where

    table_owner = upper(nvl('&&Owner',user))

and table_name = upper('&&Table_name')

order by SUBPARTITION_POSITION

/

break on partition_name

select

    p.PARTITION_NAME,

    t.SUBPARTITION_NAME,

    t.COLUMN_NAME,

    t.NUM_DISTINCT,

    t.DENSITY,

    t.NUM_BUCKETS,

    t.NUM_NULLS,

    t.GLOBAL_STATS,

    t.USER_STATS,

    t.SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from

    dba_SUBPART_COL_STATISTICS t,

    dba_tab_subpartitions p

where

    t.table_name = upper('&Table_name')

and t.owner = upper(nvl('&Owner',user))

and t.subpartition_name = p.subpartition_name

and t.owner = p.table_owner

and t.table_name=p.table_name

/

break on partition_name

select

    t.INDEX_NAME,

    t.PARTITION_NAME,

    t.SUBPARTITION_NAME,

    t.BLEVEL BLev,

    t.LEAF_BLOCKS,

    t.DISTINCT_KEYS,

    t.NUM_ROWS,

    t.AVG_LEAF_BLOCKS_PER_KEY,

    t.AVG_DATA_BLOCKS_PER_KEY,

    t.CLUSTERING_FACTOR,

    t.GLOBAL_STATS,

    t.USER_STATS,

    t.SAMPLE_SIZE,

    to_char(t.last_analyzed,'MM-DD-YYYY')

from

    dba_ind_subpartitions t,

    dba_indexes i

where

    i.table_name = upper('&Table_name')

and i.table_owner = upper(nvl('&Owner',user))

and i.owner = t.index_owner

and i.index_name=t.index_name

/

clear breaks

set echo on