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HomeDatabaseMysql Tutorial初窥InnoDB的Memcached插件

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

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,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(当然也可以禁止):

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

说明:以后一旦修改了原本已存在的Memcached插件的配置信息,均需要使用如上命令来重启Memcached插件(先uninstall,再install),以便让修改生效。

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` text 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。

    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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