从这里可以看出,在唯一列上的等值查询,位图索引与btree索引的效率相当。 下面,我们在针对范围查询来进行测试。 [sql]view plaincopyprint? SQL> create bitmap index bm_random on emp_random(empno); 索引已创建。 SQL> analyze table emp_random compute statistics for table for all indexes for all columns;...
insert into tb_btree2 selecttrunc(dbms_random.value(1,100001)) , 'name'||level from dual connect by level<= 100000; insert into tb_bitmap2 select* from tb_btree2 ; --create index create index tb_btree2_idx1on tb_btree2(id) ; create bitmap indextb_bitmap2_btidx1 on tb_bitmap...
Oracle编程高手箴言:位图索引(Bitmap Index)的故事 您如果熟悉 Oracle 数据库,我想您对 Thomas Kyte 的大名一定不会陌生。 Tomas 主持的 asktom.oracle.com 网站享誉 Oracle 界数十年,绝非幸致。最近在图书馆借到这位 Oracle 绝顶高手编著的《 Expert Oracle Database Architecture-9i and 10g programming Techniques...
根据oracle的执行计划,肯定是cost最小的,但是它很多时候忽略了一致性读等其他条件,导致这个执行计划并非像oracle想象的那样最优,因为把btree index转为为bitmap index执行,需要消耗更多的cpu,特别是在cpu比较紧张的系统中,所以这样的情况如果发生在oltp系统中,一般都需要解决。 本例的解决办法是删除唯一度低的index,建...
I want to compare the features available in Oracle and Mysql(and alsternatives). Like Table Partitioning(Hash, range, Composite). Indexing (BTree, Bitmap, Context search). Index orangainzed Tables Stored Packages. Pls. do let me know where i can get this info. ...
(1) bit in one and only one of the bit vectors. Now we search using the bitmap index. SELECT COUNT(*) FROM T WHERE C IS NULL; ... Do this by counting the 1 bits in the NULL bit vector. The good things that we can note from this example are that the index is small (a ...
highgo=# create index idx_t_lei_1 on t_lei(oid) highgo-# ; CREATE INDEX highgo=# explain analyze select * from t_lei where oid<100 and relname='dump'; QUERY PLAN --- Bitmap Heap Scan on t_lei (cost=3.90..14.75 rows=1 width=68) (actual time=0.089..0.089 rows=0 loops=1) ...