索引条目的最后一部分则是由多个bit位所组成的bitmap,每个bit位就对应一条记录。 当发出where c1='01'这样的SQL语句时,Oracle会去搜索01所在的索引条目,然后扫描该索引条目中的bitmap里所有的bit位。第一个bit位为1,则说明第一条记录上的C1值为01,于是返回第一条记录所在的ROWID(根据该索引条目里记录的...
(1) 建立B*tree索引 3:11:08 SQL>create index emp1_job_ind on emp1(job); (2)分析索引结构 3:11:08 SQL> ANALYZE INDEX EMP1_JOB_IND VALIDATE STRUCTURE; Index analyzed. (3)查看索引存储信息 03:11:41 SQL> SELECT BLEVEL,LEAF_BLOCKS,NUM_ROWS FROM USER_INDEXES 03:12:12 2 WHERE INDEX_...
testidx_c 表分别为 object_name 和 object_type 列创建 Bitmap 索引。 测试B-tree 索引 首先,testidx_a表,不创建任何索引。其次,为testidx_b表的object_name和object_type列分别建立idx_tb_on和idx_tb_ot的 B-tree 索引。Oracle 默认创建 B-tree 索引。 代码段三: SQL>createindexidx_tb_ononTESTIDX_...
If you define this culumn as a primary key, you will create a B-tree index and not a bitmap index because Oracle does not support bitmap primary key indexes. To analyze the behavior of these indexes, we will perform the fullowing steps:1. On TEST_NORMAL: a. Create a bitmap index...
CREATEINDEXONtest (lower(name)); 查看执行计划 EXPLAINSELECT*FROMtestWHERElower(name)='a1'; QUERY PLAN---Bitmap Heap Scanontest (cost=12.17..571.91rows=500width=10) Recheck Cond: (lower((name)::text)='a1'::text)->Bitmap Index Scanontest_lower_idx (cost=0.00..12.04rows=500width=0)...
该指标意思是索引分裂在寻找空块时,扫描大量的“可复用的free block”,分裂需要的free block优先会找索引中100% free的索引块,ASSM管理表空间中bitmap管理区分0~25%、25%~50%、50%~75%和75%~100%四种使用率的索引块。寻找“可复用的free block”会把Free Space 75%~100%的索引块都会扫描一遍,从而找到真正...
B-tree索引(Oracle默认建立B-tree索引) *** B-tree聚集索引(B-tree cluster indexes) Hash聚集索引(Hash cluster indexes) 反向索引(Reverse key indexes) 位图索引(Bitmap indexes) *** 位图连接索引(Bitmap join indexes) 创建索引的语法: CREATE [UNIQUE] INDEX 索引名 ON 表名(列的列表) ...
一. B-Tree Index原理 官网说明: No index structure can satisfy all needs, butthe self-balancing B-tree index comes closest to optimizing the performance of searches on large sets of data.Each B-tree node holds multiple keys and pointers. The maximum number of keys in a node supported by ...
Comer notes that the B+ tree was used in IBM's VSAM data access software and he refers to an IBM published article from 1973. [edit] See also Binary Search Tree B# Tree B-tree Bitmap index Divide and conquer algorithm [edit] References ^ a b c d e Ramakrishnan Raghu, Gehrke ...
alter session set events 'immediate trace name treedump level INDEX_OBJECT_ID'; 比如,对于上面的例子来说,我们把创建在goodid上的名为idx_warecountd_goodid的索引转储出来。 SQL> select object_id from user_objects where object_name='IDX_WARECOUNTD_GOODID'; ...