MySQL 5.7版本新特性连载（四）

本文将和大家一起分享下5.7的新特性，不过我们要先从即将被删除的特性以及建议不再使用的特性说起。根据这些情况，我们在新版本及以后的版本中，应该不再使用，避免未来产生兼容性问题。

本文是基于MySQL-5.7.7-rc版本，未来可能 还会发生更多变化。

【新特性实践】

[yejr@imysql.com]> select @@sql_mode; -- 查看默认的 sql_mode +-----------------------------------------------------------------------------------+ | @@sql_mode | +-----------------------------------------------------------------------------------+ | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | +-----------------------------------------------------------------------------------+  [yejr@imysql.com]> insert into t_char select 0, repeat('x',50); -- 插入50个字符 ERROR 1406 (22001): Data too long for column 'uname' at row 1  [yejr@imysql.com]> set sql_mode = 'ONLY_FULL_GROUP_BY,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';  -- 修改本 session 的 sql_mode Query OK, 0 rows affected (0.00 sec)  [yejr@imysql.com]> select @@sql_mode; -- 去掉 STRICT_TRANS_TABLES 模式后 +---------------------------------------------------------------+ | @@sql_mode | +---------------------------------------------------------------+ | ONLY_FULL_GROUP_BY,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | +---------------------------------------------------------------+  [yejr@imysql.com]> insert into t_char select 0, repeat('x',50); Query OK, 1 row affected, 1 warning (0.00 sec)  -- 提示有告警信息 Records: 1 Duplicates: 0 Warnings: 1  [yejr@imysql.com]> show warnings; +---------+------+--------------------------------------------+ | Level | Code | Message | +---------+------+--------------------------------------------+ | Warning | 1265 | Data truncated for column 'uname' at row 1 | +---------+------+--------------------------------------------+

因为 uname 字段的长度为 40 个字符。

2、 优化online操作 ， 例如 修改buffer pool 、 修改索引名（非主键）、修改REPLICATION FILTER、修改MATER而无需关闭SLAVE线程 等众多特性。

可以在线修改buffer pool对DBA来说实在太方便了，实例运行过程中可以动态调整，避免事先分配不合理的情况，不过 innodb_buffer_pool_instances 不能修改，而且在 innodb_buffer_pool_instances 大于 1 时，也不能将 buffer pool 调整到 1GB 以内，需要稍加注意。

如果是把buffer pool加大，其过程大致是：

1、以innodb_buffer_pool_chunk_size为单位，分配新的内存pages； 2、扩展buffer pool的AHI(adaptive hash index)链表，将新分配的pages包含进来； 3、将新分配的pages添加到free list中；

如果是把buffer pool加大，其过程则大致是：

1、重整buffer pool，准备回收pages； 2、以innodb_buffer_pool_chunk_size为单位，释放删除这些pages（这个过程会有一点点耗时）； 3、调整AHI链表，使用新的内存地址。

实际测试时，发现在线修改 buffer poo 的代价并不大，SQL命令提交完毕后都是瞬间完成，而后台进程的耗时也并不太久。在一个并发128线程跑tpcc压测的环境中，将 buffer pool 从32G扩展到48G，后台线程耗时 3秒，而从 48G 缩减回 32G 则耗时 18秒，期间压测的事务未发生任何锁等待。

-- 演示1：从 1G 扩大到 16G [yejr@imysql.com]> SET GLOBAL innodb_buffer_pool_size = 51539607552;  Query OK, 0 rows affected (0.00 sec)  -- 看看日志记录 09:21:19.460543Z 0 [Note] InnoDB: Resizing buffer pool from 1073741824 to 17179869184. (unit=134217728) 09:21:19.468069Z 0 [Note] InnoDB: disabled adaptive hash index. 09:21:20.760724Z 0 [Note] InnoDB: buffer pool 0 : 60 chunks (491511 blocks) were added. 09:21:21.922869Z 0 [Note] InnoDB: buffer pool 1 : 60 chunks (491520 blocks) were added. 09:21:21.935114Z 0 [Note] InnoDB: buffer pool 0 : hash tables were resized. 09:21:21.947264Z 0 [Note] InnoDB: buffer pool 1 : hash tables were resized. 09:21:22.203031Z 0 [Note] InnoDB: Resized hash tables at lock_sys, adaptive hash index, dictionary. 09:21:22.203062Z 0 [Note] InnoDB: Completed to resize buffer pool from 1073741824 to 17179869184. 09:21:22.203075Z 0 [Note] InnoDB: Re-enabled adaptive hash index.  -- 演示2：从 16G 缩减到 1G [yejr@imysql.com]> SET GLOBAL innodb_buffer_pool_size = 1073741824; Query OK, 0 rows affected (0.00 sec)  -- 看看日志记录 09:22:55.591669Z 0 [Note] InnoDB: Resizing buffer pool from 17179869184 to 1073741824. (unit=134217728) 09:22:55.680836Z 0 [Note] InnoDB: disabled adaptive hash index. 09:22:55.680864Z 0 [Note] InnoDB: buffer pool 0 : start to withdraw the last 491511 blocks. 09:22:55.765778Z 0 [Note] InnoDB: buffer pool 0 : withdrew 489812 blocks from free list. Tried to relocate 1698 pages (491510/491511). 09:22:55.774492Z 0 [Note] InnoDB: buffer pool 0 : withdrew 0 blocks from free list. Tried to relocate 1 pages (491511/491511). 09:22:55.782745Z 0 [Note] InnoDB: buffer pool 0 : withdrawn target 491511 blocks. 09:22:55.782786Z 0 [Note] InnoDB: buffer pool 1 : start to withdraw the last 491520 blocks. 09:22:55.892068Z 0 [Note] InnoDB: buffer pool 1 : withdrew 489350 blocks from free list. Tried to relocate 2166 pages (491517/491520). 09:22:55.900743Z 0 [Note] InnoDB: buffer pool 1 : withdrew 0 blocks from free list. Tried to relocate 2 pages (491519/491520). 09:22:55.908257Z 0 [Note] InnoDB: buffer pool 1 : withdrew 0 blocks from free list. Tried to relocate 0 pages (491519/491520). 09:22:55.915778Z 0 [Note] InnoDB: buffer pool 1 : withdrew 0 blocks from free list. Tried to relocate 1 pages (491520/491520). 09:22:55.923836Z 0 [Note] InnoDB: buffer pool 1 : withdrawn target 491520 blocks. 09:22:56.149172Z 0 [Note] InnoDB: buffer pool 0 : 60 chunks (491511 blocks) were freed. 09:22:56.308997Z 0 [Note] InnoDB: buffer pool 1 : 60 chunks (491520 blocks) were freed. 09:22:56.316258Z 0 [Note] InnoDB: buffer pool 0 : hash tables were resized. 09:22:56.324027Z 0 [Note] InnoDB: buffer pool 1 : hash tables were resized. 09:22:56.393589Z 0 [Note] InnoDB: Resized hash tables at lock_sys, adaptive hash index, dictionary. 09:22:56.393616Z 0 [Note] InnoDB: Completed to resize buffer pool from 17179869184 to 1073741824. 09:22:56.393628Z 0 [Note] InnoDB: Re-enabled adaptive hash index.

再来看下在线修改非主键索引名，直接用 ALTER TABLE RENAME INDEX 语法即可。

【新特性实践】

例如下面的SQL语法：

[yejr@imysql.com]> ALTER TABLE orders RENAME INDEX idx1 TO idxxx1;   Query OK, 0 rows affected (0.11 sec) Records: 0 Duplicates: 0 Warnings: 0

可以看到，几乎瞬间完成，尽管我在执行这个SQL时正跑着64个并发tpcc压测。

延伸阅读：

1.4 What Is New in MySQL 5.7

整理的比较仓促，若有遗漏或失误，请留言回复，谢谢！