1. 背景

* 在InnoDB存儲引擎中，表都是根據主鍵順序組織存放的，這種存儲方式的表稱為索引組織表(index organized table IOT)。

* 在InnoDB存儲引擎中，每張表都有個主鍵(Primary key)，如果在創建表時沒有地定義主鍵，則InnoDB存儲引擎會選擇表中符合條件的列或隱式創建主鍵。

2. 環境

mysql> select version();
+------------+
| version()  |
+------------+
| 5.6.36-log |
+------------+
1 row in set (0.02 sec)

mysql> select database();
+------------+
| database() |
+------------+
| mytest     |
+------------+
1 row in set (0.00 sec)

mysql> show tables;
+------------------+
| Tables_in_mytest |
+------------------+
| customer         |
| district         |
| history          |
| item             |
| new_orders       |
| order_line       |
| orders           |
| stock            |
| warehouse        |
+------------------+
9 rows in set (0.00 sec)

mysql> show variables like ‘innodb_page_size‘;
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| innodb_page_size | 8192  |
+------------------+-------+
1 row in set (0.04 sec)

3. 查詢

* 查詢每張表primary key對應的root page_no

mysql> select t.table_id table_id, t.name table_name, i.page_no root_page_no 
from information_schema.INNODB_SYS_INDEXES i, information_schema.INNODB_SYS_TABLES t 
where i.table_id = t.table_id 
and i.name = ‘PRIMARY‘ 
and t.name like ‘mytest/%‘;
+----------+-------------------+--------------+
| table_id | table_name        | root_page_no |
+----------+-------------------+--------------+
|       22 | mytest/customer   |            3 |
|       21 | mytest/district   |            3 |
|       27 | mytest/item       |            3 |
|       24 | mytest/new_orders |            3 |
|       26 | mytest/order_line |            3 |
|       25 | mytest/orders     |            3 |
|       28 | mytest/stock      |            3 |
|       20 | mytest/warehouse  |            3 |
+----------+-------------------+--------------+
8 rows in set (0.04 sec)

* 查詢order_line表數據量

mysql> select count(1) from order_line;
+----------+
| count(1) |
+----------+
|  6001615 |
+----------+
1 row in set (9.03 sec)

* 通過表數據文件order_line.ibd獲取高度 [跳過 root_page_no * innodb_page_size + 64, 獲取2字節長度就是樹的高度]

由此可得樹的高度為3, 高度標記從0開始

[[email protected] src]# hexdump -s 24640 -n 2 -C /data/mysql_data_6/mytest/order_line.ibd;
00006040  00 02                                             |..|
00006042

4. B+Tree

5. xxx

本文出自 “sea” 博客，請務必保留此出處http://lisea.blog.51cto.com/5491873/1949144

InnoDB--------查詢IOT B+ Tree的高度