Let’s talk about the storage location and storage structure of MySQL data

MySQL is a powerful relational database management system that is widely used in various applications, such as e-commerce websites, social media, financial systems, and enterprise systems. When we use MySQL, we often face this question: Where does the MySQL data exist? Let's introduce the storage location and storage structure of MySQL data in detail.

1. MySQL data storage location

MySQL data is stored on the disk, not in memory. When we create a MySQL database, we actually create a folder on the disk that contains all the tables and data of the database. MySQL stores these files in a system folder called the data directory. In Linux systems, this directory is usually located in the /var/lib/mysql directory. In Windows systems, this directory is usually located in the C:\ProgramData\MySQL\MySQL Server 8.0\data directory.

2. MySQL data storage structure

MySQL stores data in tables. Each table consists of one or more rows, and each row consists of one or more columns. Each column has its own data type, which can be integer, float, date or string, etc.

1. Database files

In MySQL, each database has an independent data directory, which contains all the files of the database. The name of the database file is the same as the database name, and the suffix is ​​usually frm, MYD and MYI. The frm file is a file that stores table definitions, the MYD file is a file that stores table data, and the MYI file is a file that stores table indexes. These files are usually stored in the data directory in a folder with the same name as the database.

2. Table storage structure

Each table consists of one or more data files, one of which is the table definition file (.frm file), and the rest are data files (.MYD files) and index files (.MYI files). The table definition file saves the structure of the table, including column names, data types, constraints and other information. The data files contain the actual table data, while the index files contain the indexes used to quickly retrieve the data.

3. Index storage structure

MySQL uses two data structures, B-tree and B-tree, to store indexes. B-tree is a multi-way search tree that divides data into multiple nodes and uses a tree to maintain the hierarchical structure of these nodes. B-tree nodes usually contain multiple key-value pairs, each key-value pair contains a key and the corresponding pointer or data block address. B-tree is a variant of B-tree, which adds a sequential access pointer to the B-tree to optimize the efficiency of sequential queries.

4. Row storage structure

MySQL uses a storage engine called InnoDB to store row data. InnoDB uses a technology called clustered index to store row data and indexes. A clustered index is a special index that stores data on disk in key order. In InnoDB, each table must have a primary key, which will be used as the key of the clustered index. Therefore, InnoDB stores data and indexes in the same data file respectively, which can improve query efficiency.

In short, MySQL data is stored on the disk, and the data storage structure includes database files, table storage structures, index storage structures, and row storage structures. Understanding the storage location and storage structure of MySQL data is very important for developers. It can help us optimize the performance of the database, reduce the risk of data loss, and improve the security and reliability of the data.

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