MySQL 设置变量的副作用
动态设置变量可能导致意外的副作用，例如从缓冲中刷新脏块。务必小心那些可以在线更改的设置，因为它们可能导致数据库做大量的工作。有时可以通过名称推断一个变
。）
总的来说，设置很大的排序缓存代价可能非常高，所以除非确定必须要这么大，否则不要增加排序缓存的大小。
如果查询必须使用一个更大的排序缓存才能比较好地执行，可以在查询执行前增加sort_buffer_size的值，执行完成后恢复DEFAULT。
eg：
SET @@session.sort_buffer_size :=可以将类似的代码封在函数中以方便使用。其它可以设置的单个连接级别的变量有read_buffer_size，read_rnd_buffer_size，tmp_table_size，以及myisam_sort_buffer_size。
特别说明：本文章是来自
个人感悟：理解可动态更改的变量产生的影响是蛮重要的，一不小心，可能导致负载飞一般的暴涨，CPU刷刷的飙升，香港虚拟主机，甚至宕机。
糗事：本人曾在线上数据库动态修改query_cache_szie的值，本来server的负载都40-50的样子啦，当时也不没考虑那么多，香港服务器租用，就直接改了，负载瞬间飙升到了200多，那个汗啊，，，
好的东西是拿出来分享的，香港空间，那样它就会更美！！！
本文出自 “Focus on the database” 博客，请务必保留此出处
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
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
When might a full table scan be faster than using an index in MySQL?
Apr 09, 2025 am 12:05 AM
Full table scanning may be faster in MySQL than using indexes. Specific cases include: 1) the data volume is small; 2) when the query returns a large amount of data; 3) when the index column is not highly selective; 4) when the complex query. By analyzing query plans, optimizing indexes, avoiding over-index and regularly maintaining tables, you can make the best choices in practical applications.
Can I install mysql on Windows 7
Apr 08, 2025 pm 03:21 PM
Yes, MySQL can be installed on Windows 7, and although Microsoft has stopped supporting Windows 7, MySQL is still compatible with it. However, the following points should be noted during the installation process: Download the MySQL installer for Windows. Select the appropriate version of MySQL (community or enterprise). Select the appropriate installation directory and character set during the installation process. Set the root user password and keep it properly. Connect to the database for testing. Note the compatibility and security issues on Windows 7, and it is recommended to upgrade to a supported operating system.
Explain InnoDB Full-Text Search capabilities.
Apr 02, 2025 pm 06:09 PM
InnoDB's full-text search capabilities are very powerful, which can significantly improve database query efficiency and ability to process large amounts of text data. 1) InnoDB implements full-text search through inverted indexing, supporting basic and advanced search queries. 2) Use MATCH and AGAINST keywords to search, support Boolean mode and phrase search. 3) Optimization methods include using word segmentation technology, periodic rebuilding of indexes and adjusting cache size to improve performance and accuracy.
MySQL: Simple Concepts for Easy Learning
Apr 10, 2025 am 09:29 AM
MySQL is an open source relational database management system. 1) Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2) Basic operations: INSERT, UPDATE, DELETE and SELECT. 3) Advanced operations: JOIN, subquery and transaction processing. 4) Debugging skills: Check syntax, data type and permissions. 5) Optimization suggestions: Use indexes, avoid SELECT* and use transactions.
Difference between clustered index and non-clustered index (secondary index) in InnoDB.
Apr 02, 2025 pm 06:25 PM
The difference between clustered index and non-clustered index is: 1. Clustered index stores data rows in the index structure, which is suitable for querying by primary key and range. 2. The non-clustered index stores index key values and pointers to data rows, and is suitable for non-primary key column queries.
Can mysql and mariadb coexist
Apr 08, 2025 pm 02:27 PM
MySQL and MariaDB can coexist, but need to be configured with caution. The key is to allocate different port numbers and data directories to each database, and adjust parameters such as memory allocation and cache size. Connection pooling, application configuration, and version differences also need to be considered and need to be carefully tested and planned to avoid pitfalls. Running two databases simultaneously can cause performance problems in situations where resources are limited.
The relationship between mysql user and database
Apr 08, 2025 pm 07:15 PM
In MySQL database, the relationship between the user and the database is defined by permissions and tables. The user has a username and password to access the database. Permissions are granted through the GRANT command, while the table is created by the CREATE TABLE command. To establish a relationship between a user and a database, you need to create a database, create a user, and then grant permissions.
RDS MySQL integration with Redshift zero ETL
Apr 08, 2025 pm 07:06 PM
Data Integration Simplification: AmazonRDSMySQL and Redshift's zero ETL integration Efficient data integration is at the heart of a data-driven organization. Traditional ETL (extract, convert, load) processes are complex and time-consuming, especially when integrating databases (such as AmazonRDSMySQL) with data warehouses (such as Redshift). However, AWS provides zero ETL integration solutions that have completely changed this situation, providing a simplified, near-real-time solution for data migration from RDSMySQL to Redshift. This article will dive into RDSMySQL zero ETL integration with Redshift, explaining how it works and the advantages it brings to data engineers and developers.
