1.34 InnoDB Tablespaces

1. What Is a Tablespace - A tablespace is an abstract concept - Logically - It can be imagined as a pool of pages - Physically - For the system tablespace, it corresponds to one or more actual files in the file system - By default, InnoDB creates a file named ibdata1 with a size of 12M under the data directory, and the size grows automatically - For each file-per-table tablespace, it corresponds to an actual file named table_name.ibd in the file system 2. Tablespace Structure

DatabasesCreated 06/07/2021Updated 02/26/20221 min readhistorical

This is a historical learning note and may contain outdated or incomplete understanding.

1. What Is a Tablespace

A tablespace is an abstract concept.
Logically:
- it can be imagined as a pool of pages.
Physically:
- for the system tablespace, it corresponds to one or more actual files in the file system;
  - by default, InnoDB creates a file named ibdata1 with a size of 12M under the data directory, and its size grows automatically;
- for each file-per-table tablespace, it corresponds to an actual file named table_name.ibd in the file system.

2. Tablespace Structure

2.1. Pages

A tablespace can be imagined as a pool of pages.
MySQL Pages.md

2.2. Extents

2.2.1. What Is an Extent

A tablespace is divided into many contiguous extents, and each extent consists of 64 pages by default.
Every 256 extents are divided into a group, and the types of the first few pages in each group are fixed.

2.2.2. Why Divide into Extents

Pages themselves are sufficient, but pages are stored discretely and use random I/O.
An extent consists of 64 pages that are contiguous in physical location and uses sequential I/O.

2.3. Segments

Leaf nodes have their own extents, and non-leaf nodes also have their own extents.
The collection of extents that store leaf nodes is a segment, and the collection of extents that store non-leaf nodes is also a segment.