dbms_stats 导入导出 表级别 统计信息

           dbms_stats 导入导出 schema 级别统计信息

 

1、创建演示环境

 scott@USBO> select * from v$version where rownum<2;

 BANNER
 --------------------------------------------------------------------------------
 Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production

 --创建演示表，并插入所有sys用户的表记录
 scott@USBO> create table t1 nologging tablespace tbs1 as select * from dba_objects where owner='SYS' and object_type='TABLE';

 --添加所有非sys的记录
 scott@USBO> insert into t1 select * from dba_objects where owner <>'SYS';

 43172 rows created.

 scott@USBO> commit;
 scott@USBO> create index i_t1_owner on t1(owner);      --->添加索引

 --收集统计信息
 scott@USBO> exec dbms_stats.gather_table_stats('SCOTT','T1',cascade=>true);

 PL/SQL procedure successfully completed.

 --此时表上sys用户的表位1001个
 scott@USBO> select owner,count(*) from t1 where owner='SYS' group by owner;

 OWNER                            COUNT(*)
 ------------------------------ ----------
 SYS                                  1001

 --下面是其执行计划
 scott@USBO> set autot trace exp;
 scott@USBO> select owner,count(*) from t1 where owner='SYS' group by owner;

 Execution Plan
 ----------------------------------------------------------
 Plan hash value: 832695366

 -----------------------------------------------------------------------------------
 | Id  | Operation            | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
 -----------------------------------------------------------------------------------
 |   0 | SELECT STATEMENT     |            |     1 |     8 |     4   (0)| 00:00:01 |
 |   1 |  SORT GROUP BY NOSORT|            |     1 |     8 |     4   (0)| 00:00:01 |
 |*  2 |   INDEX RANGE SCAN   | I_T1_OWNER |  1425 | 11400 |     4   (0)| 00:00:01 |
 -----------------------------------------------------------------------------------

 scott@USBO>set autot off;

2、导出统计信息

 --首先创建用于存放统计信息的舞台表
 scott@USBO> exec dbms_stats.create_stat_table (ownname => 'SCOTT', stattab => 'ST_T1', tblspace => 'TBS1');

 PL/SQL procedure successfully completed.

 --下面使用export_table_stats过程导出统计信息，此时statid为A
 scott@USBO> exec dbms_stats.export_table_stats(ownname =>'SCOTT',tabname=>'T1',stattab=>'ST_T1',statid => 'A');

 PL/SQL procedure successfully completed.

 --插入新的记录，此时为SYS非表类型的所有对象，有30043条
 scott@USBO> insert into t1 nologging select * from dba_objects where owner='SYS' and object_type<>'TABLE';

 30043 rows created.

 scott@USBO> commit;

 --收集统计信息
 scott@USBO> exec dbms_stats.gather_table_stats('SCOTT','T1',cascade=>true);

 --再次导出统计信息，注意，此时的statid为B
 scott@USBO> exec dbms_stats.export_table_stats(ownname =>'SCOTT',tabname=>'T1',stattab=>'ST_T1',statid => 'B');

 PL/SQL procedure successfully completed.

 --下面我们分析原SQL的执行计划
 scott@USBO> set autot trace exp;
 scott@USBO> select owner,count(*) from t1 where owner='SYS' group by owner;

 Execution Plan
 ----------------------------------------------------------
 Plan hash value: 453826725

 ------------------------------------------------------------------------------------
 | Id  | Operation             | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
 ------------------------------------------------------------------------------------
 |   0 | SELECT STATEMENT      |            |     1 |     6 |    58   (0)| 00:00:01 |
 |   1 |  SORT GROUP BY NOSORT |            |     1 |     6 |    58   (0)| 00:00:01 |
 |*  2 |   INDEX FAST FULL SCAN| I_T1_OWNER | 31349 |   183K|    58   (0)| 00:00:01 |
 ------------------------------------------------------------------------------------

 --上面的执行计划中使用了最新的统计信息，而且预估的行数31349接近于表上的行数

3、导入过旧的统计信息并对比执行计划

 --下面使用import_table_stats导入之前过旧的统计信息
 scott@USBO> exec dbms_stats.import_table_stats(ownname => 'SCOTT', tabname => 'T1', stattab => 'ST_T1', -
 > statid => 'A', no_invalidate => true);

 PL/SQL procedure successfully completed.

 --再次查看原SQL的执行计划
 scott@USBO> select owner,count(*) from t1 where owner='SYS' group by owner;

 Execution Plan
 ----------------------------------------------------------
 Plan hash value: 832695366

 -----------------------------------------------------------------------------------
 | Id  | Operation            | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
 -----------------------------------------------------------------------------------
 |   0 | SELECT STATEMENT     |            |     1 |     8 |     4   (0)| 00:00:01 |
 |   1 |  SORT GROUP BY NOSORT|            |     1 |     8 |     4   (0)| 00:00:01 |
 |*  2 |   INDEX RANGE SCAN   | I_T1_OWNER |  1425 | 11400 |     4   (0)| 00:00:01 |
 -----------------------------------------------------------------------------------
 --Author : Leshami   Blog : http://blog.csdn.net/leshami
 --从上面的执行计划中来看，尽管执行计划与先前的两个执行计划相同，但预估的行数是之前的行数，只有1425条记录
 --也即是由于过时的统计信息造成的

4、批量导出表统计信息

 --下面的匿名pl/sql块可以批量导出统计信息，可以用于SQL语句涉及到多表的情形，可以把相关的表统计信息全部导出
 --需要注意的是表的名字不要超过28，因为我这里定义的统计信息备份表以"S_"开头占据了2个字符
 --可以根据自己的情形修改其代码，如添加表空间参数等。
 --对于披量导入表统计信息的脚本，大家可以参照下面的脚本修改，使用过程import_table_stats
 DECLARE
    v_table_name   VARCHAR2 (30);
    v_stat_name    VARCHAR2 (35);
    v_sql_stat     VARCHAR2 (200);
    v_schema       VARCHAR2 (30) := 'SCOTT';

    --Define your table you want to export stat
    CURSOR cur_tab
    IS
       SELECT table_name
         FROM dba_tables
        WHERE table_name IN ('EMP', 'DEPT', 'BONUS');
 BEGIN
    FOR cur_rec IN cur_tab
    LOOP
       v_stat_name := 'S_' || cur_rec.table_name;

       v_sql_stat := 'BEGIN DBMS_STATS.create_stat_table (''' || v_schema || ''' , ''' || v_stat_name || '''); END;';

       --            DBMS_OUTPUT.put_line (v_sql_stat);
       EXECUTE IMMEDIATE v_sql_stat;

       v_sql_stat := 'BEGIN DBMS_STATS.export_table_stats(''' || v_schema || ''',tabname=>''' || cur_rec.table_name || ''',stattab=>''' || v_stat_name || '''); END;';

       --        DBMS_OUTPUT.put_line (v_sql_stat);
       EXECUTE IMMEDIATE v_sql_stat;
    END LOOP;
 END;