zabbix索引被隐藏 隐藏索引标记

    假设一张表上有十几个索引，你有什么感受？显然会拖慢增、删、改的速度。不要指望开发者能建好索引。我的处理方法是先监控非常长的一段时间。看哪些索引没实用到，然后删除。

但删除以后，假设发现某一天实用，那又要又一次建，假设是大表。那就有些麻烦。如今11g提供一个新特性，不可见索引。能够建索引设置为不可见索引。CBO在评估运行计划的时候会忽略它，假设须要的时候。设置回来就可以。

    另一种用途，你在调试一条SQL语句，要建一个索引測试。而你不想影响其它的会话，用不可见索引正是时候。

SQL> drop table test purge;
 
  SQL> create table test as select * from dba_objects;
 SQL> create index ind_t_object_id on test(object_id);
 SQL> exec dbms_stats.gather_table_stats(user,'test',cascade => true);
 SQL> set autotrace traceonly
 SQL> select * from test where object_id = 10;
 运行计划
 ----------------------------------------------------------
 Plan hash value: 255872589
 -----------------------------------------------------------------------------------------------
 | Id  | Operation                   | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
 -----------------------------------------------------------------------------------------------
 |   0 | SELECT STATEMENT            |                 |     1 |   100 |     2   (0)| 00:00:01 |
 |   1 |  TABLE ACCESS BY INDEX ROWID| TEST            |     1 |   100 |     2   (0)| 00:00:01 |
 |*  2 |   INDEX RANGE SCAN          | IND_T_OBJECT_ID |     1 |       |     1   (0)| 00:00:01 |
 -----------------------------------------------------------------------------------------------
 Predicate Information (identified by operation id):
 ---------------------------------------------------
    2 - access("OBJECT_ID"=10)
 统计信息
 ----------------------------------------------------------
           1  recursive calls
           0  db block gets
           4  consistent gets
           0  physical reads
           0  redo size
        1195  bytes sent via SQL*Net to client
         337  bytes received via SQL*Net from client
           2  SQL*Net roundtrips to/from client
           0  sorts (memory)
           0  sorts (disk)
           1  rows processed


SQL> alter index ind_t_object_id invisible;
 SQL> select * from test where object_id = 10;
 运行计划
 ----------------------------------------------------------
 Plan hash value: 1357081020
 --------------------------------------------------------------------------
 | Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
 --------------------------------------------------------------------------
 |   0 | SELECT STATEMENT  |      |     1 |   100 |   209   (1)| 00:00:03 |
 |*  1 |  TABLE ACCESS FULL| TEST |     1 |   100 |   209   (1)| 00:00:03 |
 --------------------------------------------------------------------------
 Predicate Information (identified by operation id):
 ---------------------------------------------------
    1 - filter("OBJECT_ID"=10)
 统计信息
 ----------------------------------------------------------
         196  recursive calls
           0  db block gets
         567  consistent gets
           0  physical reads
           0  redo size
        1195  bytes sent via SQL*Net to client
         337  bytes received via SQL*Net from client
           2  SQL*Net roundtrips to/from client
           6  sorts (memory)
           0  sorts (disk)
           1  rows processed


 SQL> select /*+ index(test ind_t_object_id)*/ * from test where object_id = 10;
 运行计划
 ----------------------------------------------------------
 Plan hash value: 1357081020
 --------------------------------------------------------------------------
 | Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
 --------------------------------------------------------------------------
 |   0 | SELECT STATEMENT  |      |     1 |   100 |   209   (1)| 00:00:03 |
 |*  1 |  TABLE ACCESS FULL| TEST |     1 |   100 |   209   (1)| 00:00:03 |
 --------------------------------------------------------------------------
 Predicate Information (identified by operation id):
 ---------------------------------------------------
    1 - filter("OBJECT_ID"=10)
 统计信息
 ----------------------------------------------------------
           1  recursive calls
           0  db block gets
         544  consistent gets
           0  physical reads
           0  redo size
        1195  bytes sent via SQL*Net to client
         337  bytes received via SQL*Net from client
           2  SQL*Net roundtrips to/from client
           0  sorts (memory)
           0  sorts (disk)
           1  rows processed

--让数据库看到不可见索引，能够通过改变一个參数
SQL> alter session set optimizer_use_invisible_indexes = true;
 SQL> select * from test where object_id = 10;
 运行计划
 ----------------------------------------------------------
 Plan hash value: 255872589
 -----------------------------------------------------------------------------------------------
 | Id  | Operation                   | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
 -----------------------------------------------------------------------------------------------
 |   0 | SELECT STATEMENT            |                 |     1 |   100 |     2   (0)| 00:00:01 |
 |   1 |  TABLE ACCESS BY INDEX ROWID| TEST            |     1 |   100 |     2   (0)| 00:00:01 |
 |*  2 |   INDEX RANGE SCAN          | IND_T_OBJECT_ID |     1 |       |     1   (0)| 00:00:01 |
 -----------------------------------------------------------------------------------------------
 Predicate Information (identified by operation id):
 ---------------------------------------------------
    2 - access("OBJECT_ID"=10)
 统计信息
 ----------------------------------------------------------
           1  recursive calls
           0  db block gets
           4  consistent gets
           0  physical reads
           0  redo size
        1195  bytes sent via SQL*Net to client
         337  bytes received via SQL*Net from client
           2  SQL*Net roundtrips to/from client
           0  sorts (memory)
           0  sorts (disk)
           1  rows processed