Compare and select different types of locks in MySQL
MySQL is a commonly used relational database management system that is widely used in various types of applications. When multiple users access the database concurrently, in order to ensure the consistency and integrity of the data, we often need to use locks to control concurrent access operations.
MySQL provides multiple types of locks, including table-level locks and row-level locks. Different types of locks have different characteristics and applicable scenarios. This article will compare the advantages and disadvantages of various locks and provide some specific code examples.
1. Table-level lock
- Table-level read lock (Table read lock)
Syntax: LOCK TABLES table_name READ;
Features: Multiple transactions can be held simultaneously There is a read lock, but while the transaction holds the read lock, other transactions cannot acquire the write lock.
Scenario: Suitable for most scenarios where there are a lot of data reads and few write operations. - Table write lock (Table write lock)
Syntax: LOCK TABLES table_name WRITE;
Features: While a transaction holds a write lock, other transactions cannot acquire read locks or write locks.
Scenario: Suitable for scenarios that require writing operations on the entire table, such as table reconstruction, data import, etc.
2. Row-level lock
- Shared lock (Shared lock)
Syntax: SELECT * FROM table_name WHERE condition LOCK IN SHARE MODE;
Features: Multiple transactions can hold shared locks at the same time, and other transactions can acquire but cannot modify locked rows.
Scenario: Suitable for scenarios where most read operations are dominated by a small amount of write operations. - Exclusive lock (Exclusive lock)
Syntax: SELECT * FROM table_name WHERE condition FOR UPDATE;
Features: While a transaction holds an exclusive lock, other transactions cannot obtain shared locks or exclusive locks.
Scenario: Suitable for scenarios where specific rows need to be modified or deleted.
3. Lock selection and sample code
-
When multiple transactions read data from the same table at the same time, table-level read locks or sharing can be used Lock, for example:
Transaction 1:
LOCK TABLES table_name READ;
SELECT * FROM table_name;
UNLOCK TABLES;Transaction 2:
SELECT * FROM table_name; -
When you need to write to the entire table, you can use table-level write locks, for example:
Transaction 1:
LOCK TABLES table_name WRITE ;
-- Perform a write operation on the table
UNLOCK TABLES;Transaction 2:
-- Unable to obtain the write lock, need to wait for transaction 1 to complete. -
When you need to modify or delete specific rows in the table, you can use row-level locks, for example:
Transaction 1:
START TRANSACTION;
SELECT * FROM table_name WHERE condition FOR UPDATE;
--Perform modification or deletion of rows
COMMIT;Transaction 2:
START TRANSACTION;
SELECT * FROM table_name WHERE condition FOR UPDATE;
-- You need to wait for transaction 1 to complete before you can acquire the lock.
It should be noted that using locks may cause certain performance overhead and potential deadlock problems. Therefore, when designing the database architecture and writing code, we need to choose the type of lock reasonably and avoid lock conflicts to improve the concurrency performance and stability of the system.
In short, MySQL provides multiple types of locks, including table-level locks and row-level locks. Different types of locks are suitable for different scenarios. In the case of concurrent access to the database, choosing the appropriate lock is very important to ensure the consistency and integrity of the data. We need to select and use locks reasonably based on specific business needs and performance requirements, and pay attention to avoiding potential lock conflicts.
The above is the detailed content of Compare and select different types of locks in MySQL. For more information, please follow other related articles on the PHP Chinese website!

ACID attributes include atomicity, consistency, isolation and durability, and are the cornerstone of database design. 1. Atomicity ensures that the transaction is either completely successful or completely failed. 2. Consistency ensures that the database remains consistent before and after a transaction. 3. Isolation ensures that transactions do not interfere with each other. 4. Persistence ensures that data is permanently saved after transaction submission.

MySQL is not only a database management system (DBMS) but also closely related to programming languages. 1) As a DBMS, MySQL is used to store, organize and retrieve data, and optimizing indexes can improve query performance. 2) Combining SQL with programming languages, embedded in Python, using ORM tools such as SQLAlchemy can simplify operations. 3) Performance optimization includes indexing, querying, caching, library and table division and transaction management.

MySQL uses SQL commands to manage data. 1. Basic commands include SELECT, INSERT, UPDATE and DELETE. 2. Advanced usage involves JOIN, subquery and aggregate functions. 3. Common errors include syntax, logic and performance issues. 4. Optimization tips include using indexes, avoiding SELECT* and using LIMIT.

MySQL is an efficient relational database management system suitable for storing and managing data. Its advantages include high-performance queries, flexible transaction processing and rich data types. In practical applications, MySQL is often used in e-commerce platforms, social networks and content management systems, but attention should be paid to performance optimization, data security and scalability.

The relationship between SQL and MySQL is the relationship between standard languages and specific implementations. 1.SQL is a standard language used to manage and operate relational databases, allowing data addition, deletion, modification and query. 2.MySQL is a specific database management system that uses SQL as its operating language and provides efficient data storage and management.

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB


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

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

Zend Studio 13.0.1
Powerful PHP integrated development environment

SublimeText3 Linux new version
SublimeText3 Linux latest version

DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft

MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.