b*tree index的那些事(一):索引简介
B*tree index简介
结构图
从结构图可以看出，B*tree index由root block，branch block和leaf block组成。
特点
- 1.Based on modified B*Tree algorithm
- 2.Contain branch blocks and leaf blocks
- 3.Blocks contain keys and data
- 4.Keys maintained in sorted order within blocks
- 5.All leaf blocks are at the same depth
- 6.All blocks are on average 75% full
类型
|
Type |
Introduced |
|
Bitmap Indexes |
7.3.2 |
|
Index Organised Table |
8.0 |
|
Partitioned Indexes |
8.0 |
|
Reverse Key |
8.0 |
|
LOB Index |
8.0 |
|
Compressed |
8.1.5 |
|
Function-Based Indexes |
8.1.5 |
|
Descending |
8.1.5 |
|
Virtual Indexes |
8.1.5 |
|
Bitmap Join Indexes |
9.0.1 |
限制
- 1.Maximum number of B*tree levels is 24
- 2.Maximum number of columns is 16 in 7.3 and below; 32 in 8.0 and above
- 3.Maximum key lengths vary with release and block size
|
Block Size |
8.1.7 |
9.0.1 |
9.2.0 |
|
2048 |
758 |
1526 |
1478 |
|
4096 |
1578 |
3166 |
3118 |
|
8192 |
3218 |
6446 |
6398 |
|
16384 |
6498 |
13006 |
12958 |
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