Home Database Mysql Tutorial MySQL Innodb_flush_method

MySQL Innodb_flush_method

Jun 07, 2016 pm 05:20 PM
mysql basic knowledge

innodb_flush_log_at_trx_commit 决定了事务日志何时write,flushinnodb_flush_method确定了日志及数据文件如何write、flush。ld

innodb_flush_log_at_trx_commit 决定了事务日志何时write,flush

innodb_flush_method确定了日志及数据文件如何write、flush。“show   variables”显示该变量为空,那说明被设置了默认值(fdatasync)

下面我们先从Linux IO上理解一下文件是如何打开、写入、刷写到磁盘上的。

一般的文件I/O操作的三个过程open、write、fdatasync,分别是打开文件、写文件、flush操作(将文件缓存刷到磁盘上)

open 阶段:

系统调用Open(),使用 O_WRONLY| O_APPEND|O_SYNC 打开文件:

O_WRONLY表示我们以“写”的方式打开文件。

O_APPDENT以追加的方式写文件。

O_DSYNC 当向文件写入数据的时候,只有当数据写到了磁盘时,写入操作才会完成(write 才会返回成功),

与之相对应的是:

O_SYNC: 这个比O_DSYNC 更严格,把数据写入到文件时,还要把数据的一些元信息写入到磁盘比如文件长度等。

O_RSYNC 表示文件读取时,该文件的缓存必须已经flush到磁盘上。

O_DIRECT打开文件,则读/写操作都会跳过OS cache,,直接在device(disk)上读/写。(这样会降低文件的顺序读写的效率)

write阶段: 依赖与open阶段。

flush阶段:将数据刷写到磁盘上。

Fdatasync() 来确保数据文件flush到了磁盘上。

与之相对应的是:

fsync() fdatasync()两者区别等同于 O_sync 和 O_Dsync

sync()函数,将文件写入os cache 就认为写入成功(所以这个很不可靠,但性能确实提高啦)

对于linux平台的 innodb_flush_method() 设置为 Fdatasync 默认,O_sync, O_Direct

对于fdatasync:

Innodb 使用fsync()函数来刷写数据和日志。fysnc()相比fdatasync()函数需要更多的IO(元数据信息),fdatasync()在某些情况下造成Innodb崩溃。

使用fsync()的缺点是 os会缓存部分数据。因为Innodb 能够比os更能智能的管理自己的缓存区(Innodb buffer pool)。这样会造成双缓冲的浪费。(双缓冲部分的优点:有些文件系统会累计写入并执行他们,可能很有效率的排序,或者并行的写入到设备中。可以做预读取),具体情况可以具体测试一番。如果启用Innodb_file_per_table时导致每个文件都被单独使用fsync()函数,,当写入到多个表的时候不能合并到单个IO操作中。

对于O_DIRECT:

数据文件使用该标记,这个选项不会影响日志文件,对linux、freeBSD、Solaris 支持。,这个时候os不会缓存数据,完全禁止了os缓存并且使所有的读写动作直接到存储设备(避免了双缓冲),使用fsync()把文件刷写到磁盘上(该设置不能禁止RAID卡上的提前读取功能,只是禁止os的提前读取功能),对于RAID卡的缓存还是建议打开的。对于Innodb_file_per_table影响不大(热身时间会加长,满足buffer pool)

对于O_DSYNC:

这个对日志文件调用open()使用了O_SYNC标志,所有的写入是同步的,数据只有写入磁盘才算有效。它不会影响数据文件。

它不会禁止os 的缓存.

具体关系:

openlog     flush log     opendata file     flush datafile

Fdatasync                  fsync()                                    fsync()

O_DSYNC   O_SYNC                                                  fsync()

O_DIRECT                   fsync()         O_DIRECT           fsync()

linux

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
3 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Reduce the use of MySQL memory in Docker Reduce the use of MySQL memory in Docker Mar 04, 2025 pm 03:52 PM

This article explores optimizing MySQL memory usage in Docker. It discusses monitoring techniques (Docker stats, Performance Schema, external tools) and configuration strategies. These include Docker memory limits, swapping, and cgroups, alongside

How do you alter a table in MySQL using the ALTER TABLE statement? How do you alter a table in MySQL using the ALTER TABLE statement? Mar 19, 2025 pm 03:51 PM

The article discusses using MySQL's ALTER TABLE statement to modify tables, including adding/dropping columns, renaming tables/columns, and changing column data types.

How to solve the problem of mysql cannot open shared library How to solve the problem of mysql cannot open shared library Mar 04, 2025 pm 04:01 PM

This article addresses MySQL's "unable to open shared library" error. The issue stems from MySQL's inability to locate necessary shared libraries (.so/.dll files). Solutions involve verifying library installation via the system's package m

Run MySQl in Linux (with/without podman container with phpmyadmin) Run MySQl in Linux (with/without podman container with phpmyadmin) Mar 04, 2025 pm 03:54 PM

This article compares installing MySQL on Linux directly versus using Podman containers, with/without phpMyAdmin. It details installation steps for each method, emphasizing Podman's advantages in isolation, portability, and reproducibility, but also

What is SQLite? Comprehensive overview What is SQLite? Comprehensive overview Mar 04, 2025 pm 03:55 PM

This article provides a comprehensive overview of SQLite, a self-contained, serverless relational database. It details SQLite's advantages (simplicity, portability, ease of use) and disadvantages (concurrency limitations, scalability challenges). C

Running multiple MySQL versions on MacOS: A step-by-step guide Running multiple MySQL versions on MacOS: A step-by-step guide Mar 04, 2025 pm 03:49 PM

This guide demonstrates installing and managing multiple MySQL versions on macOS using Homebrew. It emphasizes using Homebrew to isolate installations, preventing conflicts. The article details installation, starting/stopping services, and best pra

How do I configure SSL/TLS encryption for MySQL connections? How do I configure SSL/TLS encryption for MySQL connections? Mar 18, 2025 pm 12:01 PM

Article discusses configuring SSL/TLS encryption for MySQL, including certificate generation and verification. Main issue is using self-signed certificates' security implications.[Character count: 159]

What are some popular MySQL GUI tools (e.g., MySQL Workbench, phpMyAdmin)? What are some popular MySQL GUI tools (e.g., MySQL Workbench, phpMyAdmin)? Mar 21, 2025 pm 06:28 PM

Article discusses popular MySQL GUI tools like MySQL Workbench and phpMyAdmin, comparing their features and suitability for beginners and advanced users.[159 characters]

See all articles