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HomeDatabaseMysql Tutorial详解MySQL下InnoDB引擎中的Memcached插件_MySQL

前些年,HandlerSocket的横空出世让人们眼前一亮,当时我还写了一篇文章介绍了其用法梗概,时至今日,由于种种原因,HandlerSocket并没有真正流行起来,不过庆幸的是MySQL官方受其启发,研发了基于InnoDB的Memcached插件,总算是在MySQL中延续了NoSQL的香火,以前单独架设Memcached服务器不仅浪费了内存,而且还必须自己维护数据的不一致问题,有了Memcached插件,这些问题都不存在了,而且借助MySQL本身的复制功能,我们可以说是变相的实现了Memcached的复制,这更是意外之喜。

 
安装

为了让文章更具完整性,我们选择从源代码安装MySQL,需要注意的是早期的版本有内存泄漏,所以推荐安装最新的稳定版,截至本文发稿时为止,最新的稳定版是5.6.13,我们就以此为例来说明,过程很简单,只要激活了WITH_INNODB_MEMCACHED即可:
 

shell> groupadd mysql
shell> useradd -r -g mysql mysql
shell> tar zxvf mysql-5.6.13.tar.gz
shell> cd mysql-5.6.13
shell> cmake . -DWITH_INNODB_MEMCACHED=ON
shell> make
shell> make install
shell> cd /usr/local/mysql
shell> chown -R mysql .
shell> chgrp -R mysql .
shell> scripts/mysql_install_db --user=mysql
shell> chown -R root .
shell> chown -R mysql data
shell> bin/mysqld_safe --user=mysql &
shell> cp support-files/mysql.server /etc/init.d/mysql.server

MySQL安装完毕后,在插件目录我们能看到innodb_engine.so和libmemcached.so:
 

mysql> SELECT @@plugin_dir;
+------------------------------+
| @@plugin_dir         |
+------------------------------+
| /usr/local/mysql/lib/plugin/ |
+------------------------------+

此外还需要导入Memcached插件所需要的表结构:
 

mysql> SOURCE /usr/local/mysql/share/innodb_memcached_config.sql

一切就绪后就可以激活Memcached插件了(当然如果需要的话也可以禁止):
 

mysql> INSTALL PLUGIN daemon_memcached soname "libmemcached.so";
mysql> UNINSTALL PLUGIN daemon_memcached;

说明:如果要重启插件的话,可以先uninstall,再install。

Memcached插件相关的配置信息如下,具体介绍可以参考官方文档:
 

mysql> SHOW VARIABLES LIKE '%memcached%';
+----------------------------------+------------------+
| Variable_name          | Value      |
+----------------------------------+------------------+
| daemon_memcached_enable_binlog  | OFF       |
| daemon_memcached_engine_lib_name | innodb_engine.so |
| daemon_memcached_engine_lib_path |         |
| daemon_memcached_option     |         |
| daemon_memcached_r_batch_size  | 1        |
| daemon_memcached_w_batch_size  | 1        |
+----------------------------------+------------------+

注意:daemon_memcached_r_batch_size和daemon_memcached_w_batch_size,这两个选项对性能影响较大,简单点说就是控制事务提交的频率,MySQL的缺省值均为1,也就是说每次都提交,这主要是从安全性考虑的,大家可以依照自己的情况来调整。

差不多了,此时Memcached端口应该准备就绪了,你可以试试看:
 

shell> echo "stats" | nc localhost 11211

换句话说,MySQL已经兼容Memcached协议,可以直接使用Memcached命令。
配置

在安装步骤里,我们导入了一个名为innodb_memcached_config.sql的脚本,它创建了一库(innodb_memcache)三表(cache_policies, config_options, containers):
 

mysql> USE innodb_memcache
mysql> SHOW TABLES;
+---------------------------+
| Tables_in_innodb_memcache |
+---------------------------+
| cache_policies      |
| config_options      |
| containers        |
+---------------------------+

cache_policies定义了缓存策略,包含如下选择:

    innodb_only:只使用InnoDB作为数据存储。
    cache-only:只使用传统的Memcached引擎作为后端存储。
    caching:二者皆使用,如果在Memcached里找不到,就查询InnoDB。

config_options定义了分隔符号:

    separator:Memcached只识别单值,使用此分隔符(|)来连接多个字段的值。
    table_map_delimiter:通过此分隔符(.)来确认表和键,如:@@table.key。

如果我们想通过Memcached协议来访问一个表,需要先在containers中配置它:
 

mysql> SELECT * FROM containers\G
*************************** 1. row ***************************
         name: aaa
       db_schema: test
       db_table: demo_test
      key_columns: c1
     value_columns: c2
         flags: c3
      cas_column: c4
  expire_time_column: c5
unique_idx_name_on_key: PRIMARY

如上已经有了test数据库的demo_test表,通过c1查询c2的值,表结构如下所示:
 

mysql> DESC test.demo_test;
+-------+---------------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+---------------------+------+-----+---------+-------+
| c1  | varchar(32)     | NO  | PRI |     |    |
| c2  | varchar(1024)    | YES |   | NULL  |    |
| c3  | int(11)       | YES |   | NULL  |    |
| c4  | bigint(20) unsigned | YES |   | NULL  |    |
| c5  | int(11)       | YES |   | NULL  |    |
+-------+---------------------+------+-----+---------+-------+

缺省情况下有一行数据:
 

mysql> SELECT * FROM test.demo_test;
+----+--------------+------+------+------+
| c1 | c2      | c3  | c4  | c5  |
+----+--------------+------+------+------+
| AA | HELLO, HELLO |  8 |  0 |  0 |
+----+--------------+------+------+------+

让我们用Memcached协议来访问看看:

 

shell> echo "get @@aaa.AA" | nc localhost 11211
VALUE @@aaa.AA 8 12
HELLO, HELLO
END

我们还可以先设定缺省访问的表,然后后续的查询就只写键名就可以了:
 

shell> (echo "get @@aaa"; echo "get AA") | nc localhost 11211
VALUE @@aaa 0 14
test/demo_test
END
VALUE AA 8 12
HELLO, HELLO
END

虽然我的例子都是通过命令行执行的,但是大家很容易就更改写成PHP之类的方法。
限制

Memcached插件用起来非常简单,不过并不是一切都很完美,比如说:当我们配置表的时候,containers表的字段,除了key_columns和value_columns以外,其它的字段,如:flags,cas_column,expire_time_column等也必须设定,可是很多时候,我们在原表中找不到贴切的字段,此时就只能对应新建三个字段,味道很恶心。

此外,containers表还有如下限制:

  •     key_columns字段的类型必须是CHAR或VARCHAR,且最大长度是250个字符。
  •     value_columns字段的类型必须是CHAR或VARCHAR或BLOB,长度不限。
  •     cas_column字段的类型必须是BIGINT。
  •     expiration_time_column字段的类型必须是INT。
  •     flags字段的类型必须是INT。

说明:随着MySQL版本的更新,这些限制可能会发生变化,请大家以实际情况为准。
实战

让我们以一个用户登录的例子来检验一下学习成果:

首先在测试数据库创建一个用户表:
 

USE `test`
 
CREATE TABLE `users` (
  `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
  `username` VARCHAR(15) NOT NULL,
  `password` VARCHAR(32) NOT NULL,
  `email` VARCHAR(50) NOT NULL,
  `flags` INT(10) UNSIGNED DEFAULT '0',
  `cas_column` BIGINT(20) UNSIGNED DEFAULT '0',
  `expire_time_column` INT(10) UNSIGNED DEFAULT '0',
  PRIMARY KEY (`id`),
  UNIQUE KEY `username` (`username`)
) ENGINE=InnoDB;

然后添加几行测试数据:
 

INSERT INTO `users` (`username`, `password`, `email`)
VALUES
('foo', 'ffffffffffffffffffffffffffffffff', 'foo@domain.com'),
('bar', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb', 'bar@domain.com');

接着在containers里配置这个表:
 

INSERT INTO innodb_memcache.containers (
  name, db_schema, db_table, key_columns, value_columns,
  flags, cas_column, expire_time_column, unique_idx_name_on_key
) VALUES (
  'default', 'test', 'users', 'username', 'password|email',
  'flags', 'cas_column', 'expire_time_column', 'username'
);

这里我们定义了多个字段(password和email)作为value_columns,并且使用竖线作为分隔符,实际上使用空格,逗号之类分隔符也可以,在innodb_config.c文件的源代码中能查到如下关于分隔符的定义,文档里并没有涵盖这些信息:
 

static const char* sep = " ;,|\n";

最后使用Memcached协议来访问一下,这里我们换个花样,执行一个MGET操作:
 

shell> echo "get foo bar" | nc localhost 11211
VALUE foo 0 47
ffffffffffffffffffffffffffffffff|foo@domain.com
VALUE bar 0 47
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb|bar@domain.com
END

既然我定义value_columns的时候设置了多个字段,那么返回数据的时候自然也返回多个字段的数据,并且它们依照innodb_memcache.config_options表中的separator字段来分隔,缺省情况下是一个竖线,如果你的字段内容里包含了竖线,那么就会和缺省值发生冲突,此时你可以更新separator的定义,比如改成三个竖线等等,需要提醒的是,修改后别忘了重启Memcached插件。

说明:因为们在配置的时候把表命名为default,所以在请求的时候不用传递表名。如果不存在default,那么会把名字按照字母顺序正序排列,排在第一位的就是缺省。

本文在使用Memcached插件的时候,所有例子均使用的是读操作,实际上写操作也是支持的,不过在实际使用时,我更倾向于写操作都通过SQL来执行,而Memcached插件仅处理KV形式的读操作,实际压力测试的结果显示,Memcached插件比SQL的方式,性能提升了百分之一百左右,虽然仍不及独立的Memcached,但考虑到其它的优势,这个结果已经很让人欣喜了,下一站,InnoDB的Memcached插件!大家做好准备吧。

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