一个unusable 的索引REBUILD后分配的block是否改变
特殊条件下，一个unusable 的索引REBUILD后分配的block是否改变
Kevin Zou
2011-8-29
一个unusable 的索引，如果要启用，必须要对其REBUILD。我们知道REBUILD一个索引时，分配给索引的BLOCK信息会发生改变。
如果是对一个新创建的TABLE和INDEX，UNUSABLE后，没有INSERT/UPDATE/DELETE的操作，REBUILD时BLOCK信息会发生改变吗？
搭建测试环境：
SQL> create table test as select * from all_objects where 0=1;
Table created.
SQL> insert into test select * from all_objects;
13540 rows created.
SQL> create index i_test on test(object_id);
Index created.
查看新创建的索引I_TEST 占用的BLOCK信息：
SQL> select segment_name, file_id, blocks, block_id
2 from dba_extents
3 where segment_name='I_TEST' and wner='SYS';
SEGMENT_NAME FILE_ID BLOCKS BLOCK_ID
-------------------- ---------- ---------- ----------
I_TEST 1 8 37481
I_TEST 1 8 37489
I_TEST 1 8 37497
I_TEST 1 8 37505
通过SQL,查看索引被引用。
SQL> set autotrace traceonly stat exp
SQL> select count(*) from test;
Execution Plan
----------------------------------------------------------
Plan hash value: 1690092453
------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 10 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | INDEX FAST FULL SCAN| I_TEST | 13540 | 10 (0)| 00:00:01 |
------------------------------------------------------------------------
Statistics
----------------------------------------------------------
138 recursive calls
0 db block gets
52 consistent gets
0 physical reads
0 redo size
413 bytes sent via SQL*Net to client
396 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
4 sorts (memory)
0 sorts (disk)
1 rows processed
|
使索引处于UNUSABLE状态；
SQL> alter index i_test unusable;
Index altered.
因为索引I_TEST不能使用，同样的SQL只能走FTS。
SQL> select count(*) from test;
Execution Plan
----------------------------------------------------------
Plan hash value: 1950795681
-------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 49 (3)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| TEST | 13540 | 49 (3)| 00:00:01 |
-------------------------------------------------------------------
Statistics
----------------------------------------------------------
138 recursive calls
0 db block gets
194 consistent gets
0 physical reads
0 redo size
413 bytes sent via SQL*Net to client
396 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
4 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> select object_id from dba_objects where object_name='I_TEST';
OBJECT_ID
----------
65949
查询到索引I_TEST的对象ID 为 65949
SQL> ALTER SESSION SET EVENTS 'immediate trace name TREEDUMP level 65949';
Session altered.
查询到索引I_TEST的对象ID 为 65949，使用tree dump可以看到索引树的结构
branch: 0x40926a 4231786 (0: nrow: 29, level: 1)
leaf: 0x40926b 4231787 (-1: nrow: 485 rrow: 485)
leaf: 0x40926c 4231788 (0: nrow: 479 rrow: 479)
leaf: 0x40926d 4231789 (1: nrow: 478 rrow: 478)
leaf: 0x40926e 4231790 (2: nrow: 479 rrow: 479)
leaf: 0x40926f 4231791 (3: nrow: 479 rrow: 479)
leaf: 0x409270 4231792 (4: nrow: 479 rrow: 479)
leaf: 0x409271 4231793 (5: nrow: 479 rrow: 479)
leaf: 0x409272 4231794 (6: nrow: 478 rrow: 478)
leaf: 0x409273 4231795 (7: nrow: 479 rrow: 479)
leaf: 0x409274 4231796 (8: nrow: 479 rrow: 479)
leaf: 0x409275 4231797 (9: nrow: 479 rrow: 479)
leaf: 0x409276 4231798 (10: nrow: 479 rrow: 479)
leaf: 0x409277 4231799 (11: nrow: 479 rrow: 479)
leaf: 0x409278 4231800 (12: nrow: 479 rrow: 479)
leaf: 0x409279 4231801 (13: nrow: 479 rrow: 479)
leaf: 0x40927a 4231802 (14: nrow: 479 rrow: 479)
leaf: 0x40927b 4231803 (15: nrow: 479 rrow: 479)
leaf: 0x40927c 4231804 (16: nrow: 479 rrow: 479)
leaf: 0x40927d 4231805 (17: nrow: 471 rrow: 471)
leaf: 0x40927e 4231806 (18: nrow: 449 rrow: 449)
leaf: 0x40927f 4231807 (19: nrow: 449 rrow: 449)
leaf: 0x409280 4231808 (20: nrow: 449 rrow: 449)
leaf: 0x409281 4231809 (21: nrow: 449 rrow: 449)
leaf: 0x409282 4231810 (22: nrow: 449 rrow: 449)
leaf: 0x409283 4231811 (23: nrow: 448 rrow: 448)
leaf: 0x409284 4231812 (24: nrow: 448 rrow: 448)
leaf: 0x409285 4231813 (25: nrow: 449 rrow: 449)
leaf: 0x409286 4231814 (26: nrow: 449 rrow: 449)
leaf: 0x409287 4231815 (27: nrow: 404 rrow: 404)
|
重新REBUILD 索引：
SQL> alter index i_test rebuild;
Index altered.
SQL> select segment_name, file_id, blocks, block_id
2 from dba_extents
3 where segment_name='I_TEST' and wner='SYS';
SEGMENT_NAME FILE_ID BLOCKS BLOCK_ID
-------------------- ---------- ---------- ----------
I_TEST 1 8 37641
I_TEST 1 8 37649
I_TEST 1 8 37657
I_TEST 1 8 37665
再次DUMP 索引的TREEDUMP：
branch: 0x40930a 4231946 (0: nrow: 29, level: 1)
leaf: 0x40930b 4231947 (-1: nrow: 485 rrow: 485)
leaf: 0x40930c 4231948 (0: nrow: 479 rrow: 479)
leaf: 0x40930d 4231949 (1: nrow: 478 rrow: 478)
leaf: 0x40930e 4231950 (2: nrow: 479 rrow: 479)
leaf: 0x40930f 4231951 (3: nrow: 479 rrow: 479)
leaf: 0x409310 4231952 (4: nrow: 479 rrow: 479)
leaf: 0x409311 4231953 (5: nrow: 479 rrow: 479)
leaf: 0x409312 4231954 (6: nrow: 478 rrow: 478)
leaf: 0x409313 4231955 (7: nrow: 479 rrow: 479)
leaf: 0x409314 4231956 (8: nrow: 479 rrow: 479)
leaf: 0x409315 4231957 (9: nrow: 479 rrow: 479)
leaf: 0x409316 4231958 (10: nrow: 479 rrow: 479)
leaf: 0x409317 4231959 (11: nrow: 479 rrow: 479)
leaf: 0x409318 4231960 (12: nrow: 479 rrow: 479)
leaf: 0x409319 4231961 (13: nrow: 479 rrow: 479)
leaf: 0x40931a 4231962 (14: nrow: 479 rrow: 479)
leaf: 0x40931b 4231963 (15: nrow: 479 rrow: 479)
leaf: 0x40931c 4231964 (16: nrow: 479 rrow: 479)
leaf: 0x40931d 4231965 (17: nrow: 471 rrow: 471)
leaf: 0x40931e 4231966 (18: nrow: 449 rrow: 449)
leaf: 0x40931f 4231967 (19: nrow: 449 rrow: 449)
leaf: 0x409320 4231968 (20: nrow: 449 rrow: 449)
leaf: 0x409321 4231969 (21: nrow: 449 rrow: 449)
leaf: 0x409322 4231970 (22: nrow: 449 rrow: 449)
leaf: 0x409323 4231971 (23: nrow: 448 rrow: 448)
leaf: 0x409324 4231972 (24: nrow: 448 rrow: 448)
leaf: 0x409325 4231973 (25: nrow: 449 rrow: 449)
leaf: 0x409326 4231974 (26: nrow: 449 rrow: 449)
leaf: 0x409327 4231975 (27: nrow: 404 rrow: 404)
看到BLOCK信息发送了变化，REBUILD前第一个BLOCK的位置是37481， 而REBUILD后改为37641。
结论：在数据没有发生变化的条件，REBUILD一个UNUSABLE的索引，BLOCK还是会改变的。
-THE END-
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