Internal maintenance of B * Tree indexes in Oracle Database

In the last week, I reviewed index-related things. In addition to reviewing concept, I also saw a good document on MOS. Share with you.

Document No.: [ID 30405.1]

This article is only concerned with B * tree indexes which are currently the most commonly used. the theory of B * tree indexes is beyond the scope of this article; for more information refer to computer science texts dealing with data structures.

This document only describes the most common B * tree indexes currently. The principle of B * tree Indexing is beyond the scope of this document. For more information, see the data structure principle of the computer.

Format of Index Blocks
~~~~~~~~~~~~~~~~~~~~~~

Index Structure (format ?)

Within a B * tree index, index blocks are either branch blocks, the upper blocks within the B * tree index, or leaf blocks, the lowest level index blocks. branch blocks contain index data that point to lower level index blocks. leaf blocks contain every indexed data value and a corresponding ROWID used to locate the actual row.

In B * tree indexes, there are two types of index blocks: branch block, leaf block, and high level, A low level (low level, at the bottom of the index ). The branch block contains the pointer that locates low-level index blocks (possibly branch blocks or leaf blocks. The leaf block contains each index data value and the corresponding rowid (used to locate the real row ).

The following is the distribution of an index block:


Index Block Format


| ----------------------------------------------------- |
|
| Index Block Header |
|
------------------------------------------------------ |
|
| Space reserved for future updates |
| And inserts of new rows with the |
| Appropriate key values |
|
| ----------------------------------------------------- | <-PCTFREE say 10
|
| Index Key Data |
|
|
|
|
|
|
|
|
|
| ----------------------------------------------------- |


B * tree Index Creation

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