本文详细介绍了Oracle数据库中如何在分区或不分区的索引组织表上创建位图索引，以及创建位图索引时所需MAPPING TABLE的作用。MAPPING TABLE是一个HEAP表，用于存储索引组织表的逻辑ROWID。通过MAPPING TABLE，查询过程能够将位图索引中的ROWID转换为对应的物理ROWID，进而访问索引组织表或普通表。此外，文章还讨论了创建和删除位图索引及MAPPING TABLE的过程，并提供了重建和恢复MAPPING TABLE的方法。
Oracle supports bitmap indexes on partitioned and nonpartitioned index-organized tables.A mapping table is required for creating bitmap indexes on an index-organized table.
The mapping table is a heap-organized table that stores logical rowids of the index-organized table. Specifically,each mapping table row stores one logical rowid for the corresponding index-organized table row. Thus,the mapping table provides one-to-one mapping between logical rowids of the index-organized table rows and physical rowids of the mapping table rows.
A bitmap index on an index-organized table is similar to that on a heap-organized table except that the rowids used in the bitmap index on an index-organized table are those of the mapping table as opposed to the base table. There is one mapping table for each index-organized table and it is used by all the bitmap indexes created on that index-organized table.
In both heap-organized and index-organized base tables, a bitmap index is accessed using a search key. If the key is found, the bitmap entry is converted to a physical rowid. In the case of heap-organized tables, this physical rowid is then used to access the base table. However, in the case of index-organized tables, the physical rowid is then used to access the mapping table. The access to the mapping table yields a logical rowid. This logical rowid is used to access the index-organized table.
Though a bitmap index on an index-organized table does not store logical rowids, it is still logical in nature.
大意是说：Oracle数据库支持在分区或者不分区的索引组织表（IOT）上创建位图索引。在向索引组织表创建位图索引的时候必须要有MAPPING TABLE。
MAPPING TABLE是一个HEAP表（即普通表），用来存储索引组织表的逻辑rowid。具体来说，MAPPING TABLE的每一行存储了一个逻辑rowid，用来关联索引组织表的行。因此，MAPPING TABLE的物理rowid和索引组织表的行之间产生了一对一的关联。因为索引组织表的rowid会经常变化，所以只有逻辑rowid，而不像普通表的行具有物理rowid，可以直接对应到具体的物理存放地点。在索引组织表上创建的位图索引和在普通HEAP表上创建的位图索引是类似的，只不过如果是索引组织表，那位图索引会使用MAPPING TABLE的rowid。在查询的时候，2种表都是通过key字段访问，在key字段找到之后，普通HEAP表会直接把key转换成rowid，然后通过rowid定位到具体的数据块中。但是如果是索引组织表，会通过key转换成rowid后，到MAPPING TABLE中去查找逻辑rowid，然后通过这个逻辑rowid去访问索引组织表里的数据。
SQL> create table t_testmap(eno number primary key,ename varchar2(10)) organization index;
Table created.
SQL> create bitmap index idx_map on t_testmap(ename);
create bitmap index idx_map on t_testmap(ename)
*
ERROR at line 1:
ORA-28669: bitmap index can not be created on an IOT with no mapping table
无法在没有mapping table的情况下给IOT创建位图索引。
SQL> create table t_testmap2(eno number primary key,ename varchar2(10)) organization index mapping table;
Table created.
SQL> create bitmap index idx_map on t_testmap2(ename);
Index created.
位图索引创建成功。
SQL> select table_name,iot_name,iot_type from user_tables;
TABLE_NAME IOT_NAME IOT_TYPE
------------------------------ ------------------------------ ---------------------
SYS_IOT_MAP_10258 T_TESTMAP2 IOT_MAPPING
T_TESTMAP2 IOT
T_TESTMAP IOT
SQL> select index_name, index_type, table_name, uniqueness from user_indexes;
INDEX_NAME INDEX_TYPE TABLE_NAME UNIQUENES
------------------------------ --------------------------- ------------------------------ ------------------
IDX_MAP BITMAP T_TESTMAP2 NONUNIQUE
SYS_IOT_TOP_10258 IOT - TOP T_TESTMAP2 UNIQUE
SYS_IOT_TOP_10256 IOT - TOP T_TESTMAP UNIQUE
这里可以看出索引组织表虽然是表，但是存储的结构是索引
SQL> drop table SYS_IOT_MAP_10258;
drop table SYS_IOT_MAP_10258
*
ERROR at line 1:
ORA-28668: cannot reference mapping table of an index-organized table
mapping table 无法被直接删除，但是可以通过move进行删除
SQL> alter table t_testmap2 move nomapping;
alter table t_testmap2 move nomapping
*
ERROR at line 1:
ORA-28670: mapping table cannot be dropped due to an existing bitmap index
在创建了bitmap index的时候，mapping table也无法被删除。
SQL> drop index idx_map;
Index dropped.
SQL> alter table t_testmap2 move nomapping;
Table altered.
SQL> select table_name,iot_name,iot_type from user_tables;
TABLE_NAME IOT_NAME IOT_TYPE
------------------------------ ------------------------------ ------------
T_TESTMAP2 IOT
T_TESTMAP IOT
这时再查询就发现mapping table被删除了。
SQL> select object_name, original_name, type from recyclebin;
no rows selected
而且这种删除不会把mapping table放入回收站。
如果因为误操作等原因想恢复mapping table，可以使用以下命令重建。
SQL> alter table t_testmap move mapping table;
Table altered.
SQL> select table_name,iot_name,iot_type from user_tables;
TABLE_NAME IOT_NAME IOT_TYPE
------------------------------ ----------------------- --------------------------
SYS_IOT_MAP_10256 T_TESTMAP IOT_MAPPING
T_TESTMAP2 IOT
T_TESTMAP IOT
此时mapping table又重新创建。
SQL> create bitmap index idx_map on t_testmap(ename);
Index created.
重新创建索引以进行下面的实验。
SQL> drop table t_testmap;
Table dropped.
SQL> select object_name, original_name, type from recyclebin;
OBJECT_NAME ORIGINAL_NAME TYPE
------------------------------ -------------------------------- -------------------------
BIN$tKX6TiUGBMLgQAB/AQATjQ==$0 IDX_MAP INDEX
BIN$tKX6TiUHBMLgQAB/AQATjQ==$0 SYS_IOT_TOP_10256 IOT TOP INDEX
SYS_IOT_MAP_10256 SYS_IOT_MAP_10256 IOT MAPPING TABLE
BIN$tKX6TiUIBMLgQAB/AQATjQ==$0 T_TESTMAP TABLE
如果直接删除表t_testmap，那么该索引组织表上关联的mapping table 和 bitmap index 会一起被放入回收站中。
SQL> flashback table t_testmap to before drop;
Flashback complete.
SQL> select table_name,iot_name,iot_type from user_tables;
TABLE_NAME IOT_NAME IOT_TYPE
------------------------------ ------------------------------ ------------
SYS_IOT_MAP_10256 T_TESTMAP IOT_MAPPING
T_TESTMAP IOT
T_TESTMAP2 IOT
SQL> select index_name, index_type, table_name from user_indexes;
INDEX_NAME INDEX_TYPE TABLE_NAME
------------------------------ -------- --------------------------- ----------------------
BIN$tKX6TiUGBMLgQAB/AQATjQ==$0 BITMAP T_TESTMAP
BIN$tKX6TiUHBMLgQAB/AQATjQ==$0 IOT - TOP T_TESTMAP
SYS_IOT_TOP_10258 IOT - TOP T_TESTMAP2
如果使用闪回的话，那么表及其关联的mapping table ， bitmap index 会一起恢复
扫一扫
999
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
