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HomeDatabaseMysql Tutorial将数据库从 MySQL 移植到 MemSQL

因为 MemSQL 完全兼容 MySQL,因此将数据从 MySQL 迁移到 MemSQL 上是非常直接的,你可以使用标准的 MySQL 工具来迁移。本例子假

因为 MemSQL 完全兼容 MySQL,因此将数据从 MySQL 迁移到 MemSQL 上是非常直接的,你可以使用标准的 MySQL 工具来迁移。

本例子假设你的 MySQL 和 MemSQL 都跑在同一台机器上,MySQL 在 3306 端口,而 MemSQL 在 3307 端口,同时假设二者都可以通过 root 账号无需密码访问。

使用 mysqldump 工具移植

mysqldump 是 MySQL 客户端最常用的数据备份工具之一,它会生成一些列创建表和插入数据的SQL语句,因此用来恢复一个数据库是最方便的。

当你确定要将数据迁移到 MemSQL 之前,有几个注意事项:

  • 大多数 MySQL 存储引擎都是使用 B-tree 来存储索引的,而 MemSQL 是使用单向无锁的 skip 列表或者无锁的哈希表。选择正确的索引数据结构对应用程序的性能会有显著的提升。其中哈希表主要适合 key-value 的查找,而 skip 列表特别适合用于复杂范围的扫描和排序(ORDER BY)。因此在进行迁移之前,你得重新审视你得表定义并确定是否能使用 MemSQL 专有的优化。默认的 BTREE 符号将被转成升序的 skip 列表。如果你需要对某个列做双向的范围扫描,你可以考虑同时增加升序和降序的索引,更多 MemSQL 的索引信息请看 indexes
  • 因为 code generation 的缘故,  MemSQL 首次加载数据库结构的速度要比 MySQL 慢,因为 MemSQL 首次加载表结构时,会生成并编译代码来实现这个表的架构,包括内存分配、插入、删除和迭代方法等等。一旦表被编译完成,MemSQL 将在整个运行期间直接使用编译好的代码。而 mysqldump 生成的 INSERT 语句也将特别编译一次。
  • mysqldump 会生成一些 MemSQL 不支持的 SQL 语句,例如不支持 UNIQUE_CHECKS,为了更好的支持 mysqldump,MemSQL 对这些不支持的语句只是予以警告,可通过调整 warn_level 变量来控制错误的级别,详情请看 Unsupported Features . 某些 CREATE TABLE 语句可能被完全阻止执行,如果你遇见这种问题,只能手工去修改表的定义SQL。
  • 如果你运行 MemSQL 的机器没有足够的内存来加载数据,服务器将会对 INSERT 语句执行报 out-of-memory 的错误信息,这种情况你只能安装更多的内存。如果你将已有的 memsqlbin 目录复制到新的机器上,那么MemSQL 会继续沿用已编译的表定义和 INSERT 语句。如果你使用的是 MemSQL 开发版,而且超过了10G 的限制,那你可以参考 memsql.com/next 来了解如何升级。
  • 建议你将数据库结构定义和数据分开独立文件存放,这样就可以在需要的时候来调整表结构,你可以使用下面命令来分别导出数据库结构和数据文件:

    $ mysqldump -h 127.0.0.1 -u root -B [database name] --no-data > schema.sql$ mysqldump -h 127.0.0.1 -u root -B [database name] --no-create-info > data.sql

    然后通过下面方法导入:

    $ mysql -h 127.0.0.1 -u root -P 3307 $ mysql -h 127.0.0.1 -u root -P 3307

    运行这些步骤时,你可以观察 memsql_tracelog (同时也输出到 stderr)  来查看执行过程中被忽略的不被支持的特性。一旦导入完成后,你可以连接到 MemSQL 并查询结果。

    转换你的应用程序

    让应用程序支持 MemSQL 非常简单,只需要改连接配置即可。

    注意

    如果你要连接到本机的 MemSQL 应该使用 127.0.0.1 而不是 localhost,,多数 MySQL 客户端可将 localhost 解析并使用 MySQL 的 socket 文件进行连接而忽略端口设置,详情请看 this page

    一旦你开始运行程序,可监控 memsql_tracelog. 一些不支持的SQL语法会在这里显示。更多 MemSQL 的 SQL Statements

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