Summary of knowledge about Mysql database
On June 8, 2017, the weather was cloudy. The mood is clear.
I have been dreaming for two consecutive nights. Last night, I dreamed of a junior high school classmate I had not contacted for a long time. I chatted with him on the way to work in the morning. The girl is currently on a business trip in Guizhou, a place with beautiful scenery. I said, "You are living a very prosperous life now." The girl said, "That's because you haven't seen my non-moisturizing side." Indeed, in life we always show our bright side to others and "disguise" our downtrodden side.
Yesterday, a blogger asked me a question on the blog and even called me a "great god". I felt very panicked because I knew very well that I was far from this "great god", so I had to Redouble your efforts and move towards the goal of "greatness".
The question asked by the blogger is about the Mysql database, which involves data engine and repair and optimize data table statements. I have never considered these before. Problem, never used. So I searched for some information to understand it, and now I summarize the information I found as follows.
1.Mysql database storage engine
Concept:
The storage engine is actually how to store data, how to index the stored data and how to Methods for updating, querying data and other technical implementations. Data in MySQL is stored in files (or in memory) using a variety of different technologies, each of these technologies uses different storage mechanisms, indexing techniques, locking levels and ultimately provides a wide range of different functionality and capabilities. In MySQL, these different technologies and supporting related functions are called storage engines.
(1) innoDB storage engine
①The mysql table of the innodb storage engine provides transaction, rollback and system crash repair capabilities and transaction security of multi-version concurrency control.
②innodb supports auto-increment columns (auto_increment). The value of an auto-increment column cannot be empty. If it is empty when used, how can it automatically grow from the existing value? If there is, it is larger than the current value. If it is still large, this value will be saved.
③The innodb storage engine supports foreign keys. The table where the foreign key is located is called the child table (or slave table), and the table it depends on is called the parent table (or main table).
④The most important thing about the innodb storage engine is that it supports transactions and transaction-related functions.
⑤The innodb storage engine supports mvcc row-level locks.
⑥The innodb storage engine index uses B+Tree.
(2) MyISAM storage engine
1) MyISAM This storage engine does not support transactions, does not support row-level locks, and only supports concurrently inserted table locks. It is mainly used for high-load select .
2) MyISAM type tables support three different storage structures: static, dynamic, and compressed.
①Static type: means that the size of the defined table column is fixed (that is, it does not contain variable-length data types such as xblob, xtext, varchar, etc.), so that mysql will automatically use it Static myisam format.
The performance of tables using static formats is relatively high because the overhead required to store data in a predetermined format during maintenance and access is very low. But this high performance is obtained in exchange for space, because it is fixed when it is defined, so no matter how big the value in the column is, the maximum value will prevail and occupy the entire space.
②Dynamic type: If the column (even if there is only one column) is defined as dynamic (xblob, xtext, varchar and other data types), then myisam will automatically use the dynamic type.
Although dynamic tables occupy less space than static tables, they reduce performance because if the content of a field changes, its position is likely to need to be moved, which will leading to the generation of fragments. As the data changes more, fragmentation will increase, and data access performance will decrease accordingly.
There are two solutions for reducing data accessibility due to fragmentation:
a. Use static data types as much as possible.
b. Frequently use the optimize table statement, which will defragment the table and recover space lost due to table updates and deletions.
If the storage engine does not support optimize table, you can dump and reload the data, which can also reduce fragmentation.
③Compressed type: If a table is created in this database that is read-only during the entire life cycle, in this case, myisam's compressed table is used to reduce the space occupied. .
3) MyISAM also uses B+tree index, but it is slightly different from Innodb in specific implementation.
(3) MEMORY storage engine
①The memory storage engine is a little different from some previous storage engines. It uses data stored in memory to create tables, and all data is also stored in memory.
②Each table based on the memory storage engine actually corresponds to a disk file. The file name and table name of the file are the same, and the type is .frm. This file only stores the structure of the table, and its data files are stored in memory, which is conducive to rapid processing of data and improves the processing capabilities of the entire table.
③The memory storage engine uses hash (HASH) index by default, which is faster than using B+Tree type. If readers want to use B-tree type, they can reference it when creating.
④Memory storage engine file data are stored in memory. If an exception occurs in the mysqld process, these data will disappear if the machine is restarted or shut down. Therefore, the life cycle of tables in the memory storage engine is very short and is generally only used once.
(4) BlackHole storage engine (black hole engine)
supports transactions and supports mvcc row-level locks. It is mainly used for logging or synchronized archiving. Unless this storage engine has a special purpose, Otherwise it is not suitable for use!
2. Optimize tables and repair tables under Mysql
With the long-term use of mysql, you can optimize it by repairing the table. During optimization, you can reduce the disk space occupied and facilitate backup.
REPAIR TABLE `table_name` Repair table OPTIMIZE TABLE `table_name` Optimize table
REPAIR TABLE - Used to repair damaged tables.
OPTIMIZE TABLE——Optimize table, used to reclaim idle database space. When the data rows on the table are deleted, the occupied disk space is not immediately reclaimed. After using the OPTIMIZE TABLE command, the space will be reclaimed and the data rows on the disk will be rearranged.
Note: It is on the disk, not the database.
Most of the time, there is no need to run OPTIMIZE TABLE. You only need to perform a data table optimization operation regularly (once a week or once a month) after deleting data rows in batches, and only run it on those specific tables. .
The above is the detailed content of Summary of knowledge about Mysql database. For more information, please follow other related articles on the PHP Chinese website!

InnoDBBufferPool reduces disk I/O by caching data and indexing pages, improving database performance. Its working principle includes: 1. Data reading: Read data from BufferPool; 2. Data writing: After modifying the data, write to BufferPool and refresh it to disk regularly; 3. Cache management: Use the LRU algorithm to manage cache pages; 4. Reading mechanism: Load adjacent data pages in advance. By sizing the BufferPool and using multiple instances, database performance can be optimized.

Compared with other programming languages, MySQL is mainly used to store and manage data, while other languages such as Python, Java, and C are used for logical processing and application development. MySQL is known for its high performance, scalability and cross-platform support, suitable for data management needs, while other languages have advantages in their respective fields such as data analytics, enterprise applications, and system programming.

MySQL is worth learning because it is a powerful open source database management system suitable for data storage, management and analysis. 1) MySQL is a relational database that uses SQL to operate data and is suitable for structured data management. 2) The SQL language is the key to interacting with MySQL and supports CRUD operations. 3) The working principle of MySQL includes client/server architecture, storage engine and query optimizer. 4) Basic usage includes creating databases and tables, and advanced usage involves joining tables using JOIN. 5) Common errors include syntax errors and permission issues, and debugging skills include checking syntax and using EXPLAIN commands. 6) Performance optimization involves the use of indexes, optimization of SQL statements and regular maintenance of databases.

MySQL is suitable for beginners to learn database skills. 1. Install MySQL server and client tools. 2. Understand basic SQL queries, such as SELECT. 3. Master data operations: create tables, insert, update, and delete data. 4. Learn advanced skills: subquery and window functions. 5. Debugging and optimization: Check syntax, use indexes, avoid SELECT*, and use LIMIT.

MySQL efficiently manages structured data through table structure and SQL query, and implements inter-table relationships through foreign keys. 1. Define the data format and type when creating a table. 2. Use foreign keys to establish relationships between tables. 3. Improve performance through indexing and query optimization. 4. Regularly backup and monitor databases to ensure data security and performance optimization.

MySQL is an open source relational database management system that is widely used in Web development. Its key features include: 1. Supports multiple storage engines, such as InnoDB and MyISAM, suitable for different scenarios; 2. Provides master-slave replication functions to facilitate load balancing and data backup; 3. Improve query efficiency through query optimization and index use.

SQL is used to interact with MySQL database to realize data addition, deletion, modification, inspection and database design. 1) SQL performs data operations through SELECT, INSERT, UPDATE, DELETE statements; 2) Use CREATE, ALTER, DROP statements for database design and management; 3) Complex queries and data analysis are implemented through SQL to improve business decision-making efficiency.

The basic operations of MySQL include creating databases, tables, and using SQL to perform CRUD operations on data. 1. Create a database: CREATEDATABASEmy_first_db; 2. Create a table: CREATETABLEbooks(idINTAUTO_INCREMENTPRIMARYKEY, titleVARCHAR(100)NOTNULL, authorVARCHAR(100)NOTNULL, published_yearINT); 3. Insert data: INSERTINTObooks(title, author, published_year)VA


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

Dreamweaver Mac version
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

WebStorm Mac version
Useful JavaScript development tools