MySQL 存储引擎
简介
MySQL中的数据用各种不同的技术存储在文件（或者内存）中；
每一种技术都使用不同的存储机制、索引技巧、锁定水平并且最终提供广泛的功能和能力；
这些不同的实现数据存储的技术在MySQL的整体架构中逻辑化为“存储引擎层”；
存储引擎，通常又被称作“表类型”（即可以在创建表时指定存储引擎，但无法对某一数据库指定存储引擎）
查看
show engines; # 显示可支持的存储引擎show table status [{from|in} Db_Name] [like ‘pattern’|where expr]; # 可显示指定数据库中指定表的状态信息# 法一：show table status like ‘classes’;# 法二：show table status where Name=’classes’/G可通过查看表的状态信息获得表所使用的存储引擎类别：
修改默认存储引擎：
# 在配置文件/etc/my.cnf中设置如下：default_storage_engine = InnoDB
各存储引擎及其特性
InnoDB
支持事务：事务日志；日志文件大小一致：如ib_logfile0和ib_logfile1支持外键支持MVCC支持聚簇索引支持行级锁：即间隙锁支持辅助索引支持自适应hash索引支持热备份不支持全文索引
MyISAM
支持全文索引支持压缩：用于实现数据仓库，能节约存储空间并提升性能支持空间索引支持表级锁：若读写操作比例为9:1或8:2，则使用MyISAM可以提高性能延迟更新索引：减少IO压力不支持事务，外键，MVCC，行级锁等崩溃后无法安全恢复数据适用场景：多读少写的数据，较小的表，能够容忍崩溃后的修改操作和数据丢失；如自带的mysql数据库中的表都是使用MyISAM存储引擎的# 建议：使用InnoDB存储引擎，并使用read commited的隔离级别，性能并不比MyISAM性能差，故推荐使用InnoDB存储引擎
ARCHIVE
仅支持insert和select支持很好的压缩功能不支持事务，不能很好的支持索引适用于：存储日志信息，或其它按时间序列实现的数据采集类的应用，如监控日志
CSV
| 12 |
将数据存储为csv格式，不支持索引仅适用于数据交换场景
|
BLACKHOLE
| 12 |
没有存储机制，任何发往此引擎的数据都会丢弃由于其会记录二进制日志，故常用于多级复制架构中作中转服务器
|
MEMORY
| 1234 |
数据保存在内存中，即是一个内存表
不支持blob和text数据类型常用于保存中间数据，如周期性的聚合数据等；也用于实现临时表
|
MRG_MYISAM
| 12 |
是MyISAM的一个变种，能够将多个MyISAM表合并为一个虚表属于传统的存储引擎，一般不常用
|
NDB
| 1 | 是MySQL Cluster中专用的存储引擎，不常用 |
第三方的存储引擎
XtraDB
增强的InnoDB，由Percona提供；用法：编译安装MySQL时，下载XtraDB的源码替换MySQL存储引擎中的InnoDB源码，并重新编译安装MySQL
PBXT
MariaDB自带此存储引擎支持引擎级别的复制，外键约束支持事务，MVCC对SSD磁盘提供适当支持
TokuDB
使用Fractal Trees索引，性能很强适用于存储大数据，拥有很好的压缩比已被引入新版本的MariaDB
列式存储引擎：
Infobright
前身为Maria，是增强版的MyISAM支持崩溃后安全恢复支持数据缓存
其它列式存储引擎
如 InfiniDB，MonetDB，LucidDB等
开源社区存储引擎:
Aria
前身为Maria，是增强版的MyISAM支持崩溃后安全恢复支持数据缓存
Groona
全文索引引擎；Mroonga是基于Groona的二次开发版
OQGraph
由Open Query研发，支持图结构的存储引擎
SphinxSE
为Sphinx全文搜索服务器提供了SQL接口
Spider
能将数据切分成不同的分片，比较高效透明的实现了分片(shard)；支持在分片上支持并行查询
选择存储引擎可参考要素
是否需要事务
备份的类型的支持(热备或冷备)
崩溃后的恢复
特有的特性(如对SSD的支持等)
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