B树叶子节点split

一、B-Tree索引的分裂
1. 创建测试表
SQL> create table split_tab (id number, name varchar2(100));
表已创建。
SQL> alter table split_tab add constraint pk_split_tab primary key (id) using index;
表已更改。
SQL> create sequence seq_alex_tab
  2  minvalue 1
  3  maxvalue 99999999
  4  start with 1
  5  increment by 1
  6  cache 200;
序列已创建。

2. 插入1万条数据
SQL> declare
    begin
    for i in 1..10000 loop
    insert into split_tab values (i, 'split');
    end loop;
   commit;
   end;  2    3    4    5    6    7
  8  /

3.搜集下统计信息:
BEGIN
  DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'SCOTT',
                                tabname          => 'SPLIT_TAB',
                                estimate_percent => 30,
                                method_opt       => 'for all columns size repeat',
                                no_invalidate    => FALSE,
                                degree           => 8,
                                cascade          => TRUE);
END;

3. 分析一下索引结构
SQL> col ratio for a20
SQL> col segment_name for a30
SQL> analyze index PK_ALEX_TAB validate structure;
索引已分析
SQL> select height,round((del_lf_rows_len/lf_rows_len)*100,2)||'%' ratio,pct_used from index_stats where name= 'PK_ALEX_TAB';
    HEIGHT RATIO                  PCT_USED
---------- -------------------- ----------
         2 0%                           93
SQL> select segment_name,bytes from user_segments where segment_name='PK_ALEX_TAB';
SEGMENT_NAME                        BYTES
------------------------------ ----------
PK_ALEX_TAB                        196608
SQL> select pct_free from user_indexes where index_name='PK_ALEX_TAB';
  PCT_FREE
----------
        10

4. DUMP出主键索引的索引树结构
SQL> select data_object_id,object_id from dba_objects where owner='SCOTT' and object_name='PK_SPLIT_TAB';

DATA_OBJECT_ID	OBJECT_ID
-------------- ----------
	 75152	    75152

SQL> alter session set events 'immediate trace name treedump level 75152';
会话已更改。

5. DUMP日志分析
----- begin tree dump
branch: 0x10206c3 16910019 (0: nrow: 18, level: 1)
   leaf: 0x10206c5 16910021 (-1: nrow: 578 rrow: 578)
   leaf: 0x10206c6 16910022 (0: nrow: 571 rrow: 571)
   leaf: 0x10206c7 16910023 (1: nrow: 571 rrow: 571)
   leaf: 0x10206c4 16910020 (2: nrow: 571 rrow: 571)
   leaf: 0x10206cd 16910029 (3: nrow: 571 rrow: 571)
   leaf: 0x10206ce 16910030 (4: nrow: 571 rrow: 571)
   leaf: 0x10206cf 16910031 (5: nrow: 571 rrow: 571)
   leaf: 0x10206c8 16910024 (6: nrow: 571 rrow: 571)
   leaf: 0x10206c9 16910025 (7: nrow: 571 rrow: 571)
   leaf: 0x10206ca 16910026 (8: nrow: 571 rrow: 571)
   leaf: 0x10206cb 16910027 (9: nrow: 571 rrow: 571)
   leaf: 0x10206cc 16910028 (10: nrow: 571 rrow: 571)
   leaf: 0x10206e1 16910049 (11: nrow: 571 rrow: 571)
   leaf: 0x10206e2 16910050 (12: nrow: 571 rrow: 571)
   leaf: 0x10206e5 16910053 (13: nrow: 571 rrow: 571)
   leaf: 0x10206e6 16910054 (14: nrow: 571 rrow: 571)
   leaf: 0x10206e7 16910055 (15: nrow: 571 rrow: 571)
   leaf: 0x10206e3 16910051 (16: nrow: 286 rrow: 286)
----- end tree dump

6. 小结
（1）可以看到主键索引只在以下叶块上进行分裂，即最右侧的叶块上进行分裂：
 leaf: 0x10206e3 16910051 (16: nrow: 286 rrow: 286)