（四）SQL MODE變化和優化online操作 · MySQL 5.7版本新特性連載

> 本文是基于MySQL-5.7.7-rc版本，未來可能還會發生更多變化。 ## 1、SQL MODE變化 a.?默認啟用 STRICT_TRANS_TABLES 模式； b. 對 ONLY_FULL_GROUP_BY 模式實現了更復雜的特性支持，并且也被默認啟用； c. 其他被默認啟用的sql mode還有 NO_ENGINE_SUBSTITUTION； ### iMySQL建議對廣大MySQL使用者而言，以往不是那么嚴格的模式還是很方便的，在5.7版本下可能會覺得略為不適，慢慢習慣吧。比如向一個20字符長度的VARCHAR列寫入30個字符，在以前會自動截斷并給個提示告警，而在5.7版本下，則直接拋出錯誤了。個人認為這倒是一個好的做法，避免各種奇葩的寫法。 ### 新特性實踐 ~~~ -- 查看默認的 sql_mode [yejr@imysql.com]>?select @@sql_mode; +-----------------------------------------------------------------------------------+ | @@sql_mode | +-----------------------------------------------------------------------------------+ | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | +-----------------------------------------------------------------------------------+ -- 插入50個字符 [yejr@imysql.com]> insert into t_char select 0, repeat('x',50); ERROR 1406 (22001): Data too long for column 'uname' at row 1 -- 修改本 session 的 sql_mode [yejr@imysql.com]> set sql_mode = 'ONLY_FULL_GROUP_BY,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'; Query OK, 0 rows affected (0.00 sec) -- 去掉 STRICT_TRANS_TABLES 模式后 [yejr@imysql.com]>?select @@sql_mode; +---------------------------------------------------------------+ | @@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 | +---------+------+--------------------------------------------+ ~~~ 因為 uname 字段的長度為 40 個字符。 ## 2、優化online操作例如修改buffer pool、修改索引名（非主鍵）、修改REPLICATION FILTER、修改MATER而無需關閉SLAVE線程?等眾多特性。可以在線修改buffer pool對DBA來說實在太方便了，實例運行過程中可以動態調整，避免事先分配不合理的情況，不過?[innodb_buffer_pool_instances](http://dev.mysql.com/doc/refman/5.7/en/innodb-parameters.html#sysvar_innodb_buffer_pool_instances)?不能修改，而且在?innodb_buffer_pool_instances 大于 1 時，也不能將 buffer pool 調整到 1GB 以內，需要稍加注意。如果是加大buffer pool，其過程大致是： ~~~ 1、以innodb_buffer_pool_chunk_size為單位，分配新的內存pages； 2、擴展buffer pool的AHI(adaptive hash index)鏈表，將新分配的pages包含進來； 3、將新分配的pages添加到free list中； ~~~ 如果是縮減buffer pool，其過程則大致是： ~~~ 1、重整buffer pool，準備回收pages； 2、以innodb_buffer_pool_chunk_size為單位，釋放刪除這些pages（這個過程會有一點點耗時）； 3、調整AHI鏈表，使用新的內存地址。 ~~~ 實際測試時，發現在線修改 buffer poo 的代價并不大，SQL命令提交完畢后都是瞬間完成，而后臺進程的耗時也并不太久。在一個并發128線程跑tpcc壓測的環境中，將 buffer pool 從32G擴展到48G，后臺線程耗時 3秒，而從 48G 縮減回 32G 則耗時 18秒，期間壓測的事務未發生任何鎖等待。 ~~~ -- 演示1：從 1G 擴大到 16G [yejr@imysql.com]> SET GLOBAL innodb_buffer_pool_size = 51539607552; Query OK, 0 rows affected (0.00 sec) -- 看看日志記錄 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：從 16G 縮減到 1G [yejr@imysql.com]> SET GLOBAL innodb_buffer_pool_size = 1073741824; Query OK, 0 rows affected (0.00 sec) -- 看看日志記錄 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. ~~~ 再來看下在線修改非主鍵索引名，直接用?ALTER TABLE RENAME INDEX?語法即可。 ### 新特性實踐例如下面的SQL語法： ~~~ [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，幾乎瞬間完成，盡管我在執行這個SQL時正跑著64個并發tpcc壓測。