oracle中默认的索引类型是B树索引。还有位图索引，反向键索引，hash索引，基于函数的索引。
本篇主要介绍B树索引，通过转储分析。对于索引的扫描类型，索引的基本操作不做详细的介绍。
系统信息：
[oracle@localhost ~]$ cat /etc/issue
Enterprise Linux Enterprise Linux Server release 5.5 (Carthage)
Kernel \r on an \m
数据库版本：
SQL> select * from v$version where rownum =1 ;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
SQL> show user;
USER 为 "HR"
SQL> desc tt;
名称 是否为空? 类型
----------------------------------------- -------- ----------------------------
ID NUMBER
NAME VARCHAR2(10)
SQL> select count(rownum) from tt;
COUNT(ROWNUM)
-------------
3670016
基于ID创建索引index_t
SQL> create index index_t on tt(id) tablespace users;
索引已创建。
SQL> select object_id from dba_objects where object_name=
2 'INDEX_T';
数据库中segment有数据段，索引段，undo段，它们和表名，索引名不是同一概念，但是名字是相同的。
OBJECT_ID
----------
76332
转储索引：
SQL> alter session set events 'immediate trace name treedump level 76332';
会话已更改。
----- begin tree dump
branch: 0x10038ab 16791723 (0: nrow: 15, level: 2)
branch: 0x100540b 16798731 (-1: nrow: 503, level: 1)
leaf: 0x10038ac 16791724 (-1: nrow: 512 rrow: 512)
leaf: 0x10038ad 16791725 (0: nrow: 512 rrow: 512)
leaf: 0x10038ae 16791726 (1: nrow: 512 rrow: 512)
leaf: 0x10038af 16791727 (2: nrow: 512 rrow: 512)
leaf: 0x10038b0 16791728 (3: nrow: 512 rrow: 512)
leaf: 0x10038b1 16791729 (4: nrow: 512 rrow: 512)
leaf: 0x10038b2 16791730 (5: nrow: 512 rrow: 512)
leaf: 0x10038b3 16791731 (6: nrow: 512 rrow: 512)
leaf: 0x10038b4 16791732 (7: nrow: 512 rrow: 512)
leaf: 0x10038b5 16791733 (8: nrow: 512 rrow: 512)
leaf: 0x10038b6 16791734 (9: nrow: 512 rrow: 512)
leaf: 0x10038b7 16791735 (10: nrow: 512 rrow: 512)
leaf: 0x10038b9 16791737 (11: nrow: 512 rrow: 512)
leaf: 0x10038ba 16791738 (12: nrow: 512 rrow: 512)
leaf: 0x10038bb 16791739 (13: nrow: 512 rrow: 512)
leaf: 0x10038bc 16791740 (14: nrow: 512 rrow: 512)
leaf: 0x10038bd 16791741 (15: nrow: 512 rrow: 512)
leaf: 0x10038be 16791742 (16: nrow: 512 rrow: 512)
leaf: 0x10038bf 16791743 (17: nrow: 512 rrow: 512)
leaf: 0x10038c0 16791744 (18: nrow: 512 rrow: 512)
leaf: 0x10038c1 16791745 (19: nrow: 512 rrow: 512)
leaf: 0x10038c2 16791746 (20: nrow: 512 rrow: 512)
leaf: 0x10038c3 16791747 (21: nrow: 512 rrow: 512)
leaf: 0x10038c4 16791748 (22: nrow: 512 rrow: 512)
leaf: 0x10038c5 16791749 (23: nrow: 512 rrow: 512)
leaf: 0x10038c6 16791750 (24: nrow: 512 rrow: 512)
leaf: 0x10038c7 16791751 (25: nrow: 512 rrow: 512)
leaf: 0x10038c9 16791753 (26: nrow: 512 rrow: 512)
leaf: 0x10038ca 16791754 (27: nrow: 512 rrow: 512)
leaf: 0x10038cb 16791755 (28: nrow: 512 rrow: 512)
leaf: 0x10038cc 16791756 (29: nrow: 512 rrow: 512)
leaf: 0x10038cd 16791757 (30: nrow: 512 rrow: 512)
leaf: 0x10038ce 16791758 (31: nrow: 512 rrow: 512)
leaf: 0x10038cf 16791759 (32: nrow: 512 rrow: 512)
leaf: 0x10038d0 16791760 (33: nrow: 512 rrow: 512)
leaf: 0x10038d1 16791761 (34: nrow: 512 rrow: 512)
leaf: 0x10038d2 16791762 (35: nrow: 512 rrow: 512)
leaf: 0x10038d3 16791763 (36: nrow: 512 rrow: 512)
leaf: 0x10038d4 16791764 (37: nrow: 512 rrow: 512)
leaf: 0x10038d5 16791765 (38: nrow: 512 rrow: 512)
leaf: 0x10038d6 16791766 (39: nrow: 512 rrow: 512)
leaf: 0x10038d7 16791767 (40: nrow: 512 rrow: 512)
leaf: 0x10038d9 16791769 (41: nrow: 512 rrow: 512)
leaf: 0x10038da 16791770 (42: nrow: 512 rrow: