解决方案 - 技术分享 | Online DDL 工具 gh-ost - 个人文章

作者：翟硕
爱可生 DBA 团队成员，负责公司 DMP 产品的运维和客户 MySQL 问题的处理。擅长数据库故障处理。对数据库技术和 python 有着浓厚的兴趣。
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Online DDL 工具 gh-ost

一、gh-ost 介绍

gh-ost 是 GitHub 发布的一款用于 MySQL 的无触发器在线模式迁移解决方案。它是可测试的，并提供暂停，动态控制/重新配置，审计和许多操作特权。它在整个迁移过程中，对主服务器产生的工作量很少，与已迁移表上的现有工作分离。

gh-ost 与所有现有的在线模式更改工具都以类似的方式操作：它们以与原始表相似的方式创建幽灵表，将数据从原始表缓慢且增量地复制到幽灵表，同时应用正在进行的更改（INSERT，DELETE，UPDATE）到幽灵表。最后，在适当的时候，它用幽灵表替换了原始表。gh-ost 使用相同的模式。但是，它与所有现有工具的不同之处在于不使用触发器。取而代之的是，gh-ost 使用二进制日志流捕获表的更改，然后将其异步应用到幽灵表。

gh-ost 承担一些其他工具留给数据库执行的任务。gh-ost 可以更好地控制迁移过程；可以真正暂停它；可以真正将迁移的写入负载与主服务器的工作负载分离。此外，它还提供了许多可操作的特权，使其更安全、可信赖且易于使用。

二、gh-ost 的三种模式架构

2.1、连接从库，在主库转换

这是 gh-ost 默认的工作模式，它会查看从库情况，找到集群的主库并且连接上去，对主库侵入最少

大体步骤是：

在主库上创建 _xxx_gho（和原表表结构一致）、_xxx_ghc（记录变更日志），并修改 _xxx_gho 表结构；
从 slave 上读取二进制日志事件，将变更应用到主库上的 _xxx_gho 表；
在主库上读源表的数据写入 _xxx_gho 表中；
在主库上完成表切换。

2.2、连接主库，在主库转换

需要使用 --allow-on-master 选项：

在主库上创建 _xxx_gho、_xxx_ghc，并修改 _xxx_gho 表结构；
从主库上读取二进制日志事件，将变更应用到主库上的 _xxx_gho 表；
在主库上读源表的数据写入 _xxx_gho 表中；
在主库上完成表切换。

2.3、在从库上测试和转换

这种模式会在从库上做修改。gh-ost 仍然会连上主库，但所有操作都是在从库上做的，不会对主库产生任何影响。在操作过程中，gh-ost 也会不时地暂停，以便从库的数据可以保持最新。

--migrate-on-replica 选项让 gh-ost 直接在从库上修改表。最终的切换过程也是在从库正常复制的状态下完成的。

--test-on-replica 表明操作只是为了测试目的。在进行最终的切换操作之前，复制会被停止。原始表和临时表会相互切换，再切换回来，最终相当于原始表没被动过。主从复制暂停的状态下，你可以检查和对比这两张表中的数据。

三、下载安装

3.1、下载

访问github，在此页面 https://github.com/github/gh-... 下载 gh-ost 最新的 rpm 安装包。

或者使用 wget 获取安装包

# 使用 wget 获取安装包
[root@10-186-61-20 ~]# wget https://github.com/github/gh-ost/releases/download/v1.0.49/gh-ost-1.0.49-1.x86_64.rpm

3.2、安装

使用 rpm 命令进行安装

# 使用rpm安装
[root@10-186-61-20 ~]# rpm -ivh gh-ost-1.0.49-1.x86_64.rpm 
Preparing...                          ################################# [100%]
Updating / installing...
   1:gh-ost-1:1.0.49-1                ################################# [100%]
# 验证是否安装成功
[root@10-186-61-20 ~]# gh-ost --version
1.0.49

四、使用

4.1、常用参数介绍

参数	解释
`allow-on-master`	允许迁移直接在主上运行，最好是在从上运行
`alter`	所要更改表结构的语句
`assume-master-host`	明确的告诉gh-ost主机的身份，这在主主复制中是有用的，或者是在tungsten-replicator中，gh-ost无法确定主
`assume-rbr`	当确定服务器采用了ROW格式的binlog时，可以显式的指定为“true”，避免重启复制，不需要super权限，否则gh-ost无法判断当前启动的复制进程是否使用了row格式进行复制，并且会重启复制以确定使用了row格式，需要用户具有super权限。
`chunk-size`	每次从原表copy数据的行数
`concurrent-rowcount`	在行复制开始后，并发的对行进行计数，然后调整行估计。当为false时，先对行计数，然后进行行复制（默认true）
`conf`	配置文件，可以写入用户名和密码： `[client]` `user=ghost` `password=123456`
`critical-load`	设置status-name=threshold，使用逗号隔开，当超过阈值时，程序会退出
`database`	转换表所在的库名
`dml-batch-size`	在单个事务中应用DML事件的批处理大小(范围为1-100)(默认为10)
`exact-rowcount`	实际计数表行，而不是估计它们(结果是更准确的进度估计)（select count(*) from ...）
`execute`	实际执行alter并迁移表。默认是noop:执行一些测试并退出
`master-password`	主服务器的密码，如果与从不同。使用`--assume-master-host`
`master-user`	主服务器的用户，如果与从不同。使用`--assume-master-host`
`max-lag-millis`	节流操作的复制延时,复制延迟超过此值时会触发节流（默认1500ms）
`max-load`	当负载超过status-name=threshold阈值时，出发节流，例如`max-load='Threads_running=100,Threads_connected=500'`
`migrate-on-replica`	让迁移在从上完整的运行，包括转换
`nice-ratio`	每次复制行休眠的时间，0代表不休眠，1 复制行1ms，休眠1ms，0.7 代表复制10ms，休眠7ms
`ok-to-drop-table`	操作完成后删除旧表
`panic-flag-file`	创建该文件时，程序立即终止
`host`	连接的MySQL主机（默认127.0.0.1）
`user`	MySQL用户
`password`	MySQL密码
`port`	MySQL端口号
`postpone-cut-over-flag-file`	当这个文件存在时，迁移将推迟交换表的最后阶段，并将继续同步ghost表。一旦文件被删除，切换/交换就可以开始执行了。
`replica-server-id`	gh-ost在创建复制线程时使用的server_id
`serve-socket-file`	socket文件位置
`switch-to-rbr`	自动切换为row格式
`table`	要进行更改的表
`test-on-replica`	在从库上测试
`test-on-replica-skip-replica-stop`	在从库上测试的时候不要停止复制
`throttle-additional-flag-file`	存在此文件时操作暂停;提示:保持默认值，用于调节多个gh-ost操作(默认值“/tmp/gh-ost.throttle”)
`throttle-control-replicas`	检查延迟的副本列表;逗号分隔的
`throttle-flag-file`	存在此文件时操作暂停;提示:使用特定于被修改的表的文件
`timestamp-old-table`	在旧表名中使用时间戳。这使得旧的表名惟一且不冲突的交叉迁移

4.2、交互式命令

需要安装 nmap-ncat 包来使用 nc 命令
使用方式为 echo "命令" | nc -U socket文件名，例如：echo status | nc -U sbtest1.gh-ost.socket

4.2.1、status

查看详细的执行状态信息。

[root@10-186-61-96 tmp]# echo status | nc -U sbtest1.gh-ost.socket
# Migrating `sbtest`.`sbtest1`; Ghost table is `sbtest`.`_sbtest1_gho`
# Migrating 10-186-61-20:3306; inspecting 10-186-61-20:3306; executing on 10-186-61-96
# Migration started at Mon Feb 17 02:08:10 +0000 2020
# chunk-size: 100000; max-lag-millis: 1500ms; dml-batch-size: 100; max-load: Threads_running=100; critical-load: Threads_running=1000; nice-ratio: 0.000000
# throttle-flag-file: /tmp/sbtest1.throttle 
# throttle-additional-flag-file: /tmp/gh-ost.throttle 
# throttle-control-replicas count: 1
# postpone-cut-over-flag-file: /tmp/sbtest1.postpone 
# panic-flag-file: /tmp/sbtest1.panic
# Serving on unix socket: /tmp/sbtest1.gh-ost.socket
Copy: 19733607/19731368 100.0%; Applied: 3425325; Backlog: 863/1000; Time: 5h18m48s(total), 5h18m48s(copy); streamer: mysql_bin.000083:192819590; Lag: 0.01s, State: throttled, 10.186.61.96:3306 replica-lag=3.686724s; ETA: due

4.2.2、sup

打印简短的状态信息。

[root@10-186-61-96 tmp]# echo sup | nc -U sbtest1.gh-ost.socket
Copy: 19833607/19731368 100.5%; Applied: 3479988; Backlog: 1000/1000; Time: 5h22m21s(total), 5h22m21s(copy); streamer: mysql_bin.000084:12427624; Lag: 1.61s, State: migrating; ETA: due

4.2.3、coordinates

打印当前检查的 binlog 的位置信息。

[root@10-186-61-96 tmp]# echo coordinates |nc -U sbtest1.gh-ost.socket 
mysql_bin.000131:10563681

4.2.4、可动态修改的参数

具体参数含义参考常用参数介绍。

chunk-size=<newsize>                 # Set a new chunk-size
dml-batch-size=<newsize>             # Set a new dml-batch-size
nice-ratio=<ratio>                   # Set a new nice-ratio, immediate sleep after each row-copy operation, float (examples: 0 is aggressive, 0.7 adds 70% runtime, 1.0 doubles runtime, 2.0 triples runtime, ...)
critical-load=<load>                 # Set a new set of max-load thresholds
max-lag-millis=<max-lag>             # Set a new replication lag threshold
replication-lag-query=<query>        # Set a new query that determines replication lag (no quotes)
max-load=<load>                      # Set a new set of max-load thresholds
throttle-query=<query>               # Set a new throttle-query (no quotes)
throttle-http=<URL>                  # Set a new throttle URL
throttle-control-replicas=<replicas> # Set a new comma delimited list of throttle control replicas

使用示例：

[root@10-186-61-96 tmp]# echo "chunk-size=10000" |nc -U sbtest1.gh-ost.socket

4.2.5、强制节流和取消节流

throttle                             # Force throttling
no-throttle                          # End forced throttling (other throttling may still apply)

4.2.6、取消推迟转换

gh-ost 默认在完成所有的 copy 动作后，不会马上转换原表和幽灵表，而是继续读取binlog应用到幽灵表中，直到发出转换的动作，所以发出此命令会立刻开始转换。

unpostpone                           # Bail out a cut-over postpone; proceed to cut-over

4.2.7、立刻停止进程

不清理现场，发出此命令后会立刻停止所有动作并退出进程。

panic                                # panic and quit without cleanup

4.2.8、help

打印出所有可用命令与解释。

[root@10-186-61-103 tmp]# echo help  | nc -U sbtest1.gh-ost.socket 
available commands:
status                               # Print a detailed status message
sup                                  # Print a short status message
coordinates                             # Print the currently inspected coordinates
chunk-size=<newsize>                 # Set a new chunk-size
dml-batch-size=<newsize>             # Set a new dml-batch-size
nice-ratio=<ratio>                   # Set a new nice-ratio, immediate sleep after each row-copy operation, float (examples: 0 is aggressive, 0.7 adds 70% runtime, 1.0 doubles runtime, 2.0 triples runtime, ...)
critical-load=<load>                 # Set a new set of max-load thresholds
max-lag-millis=<max-lag>             # Set a new replication lag threshold
replication-lag-query=<query>        # Set a new query that determines replication lag (no quotes)
max-load=<load>                      # Set a new set of max-load thresholds
throttle-query=<query>               # Set a new throttle-query (no quotes)
throttle-http=<URL>                  # Set a new throttle URL
throttle-control-replicas=<replicas> # Set a new comma delimited list of throttle control replicas
throttle                             # Force throttling
no-throttle                          # End forced throttling (other throttling may still apply)
unpostpone                           # Bail out a cut-over postpone; proceed to cut-over
panic                                # panic and quit without cleanup
help                                 # This message
- use '?' (question mark) as argument to get info rather than set. e.g. "max-load=?" will just print out current max-load.

4.3、使用示例

本示例模拟更改字段数据类型，将 sbtest1 表的 c 字段由 char(120) 改为varchar(200)。采用连接从库，在主库转换的模式架构。

4.3.1、测试环境

CPU：4C
内存：4G
操作系统版本：CentOS 7.5.1804
MySQL版本：5.7.29
MySQL架构：主从复制
- 主库：10.186.61.88:3306
- 从库：10.186.61.101:3306
gh-ost版本：1.0.49

4.3.2、准备工作

检查从库的 binlog_format 参数和 log_slave_update 参数是或否正确。

mysql> select @@global.binlog_format,@@log_slave_updates;
+------------------------+---------------------+
| @@global.binlog_format | @@log_slave_updates |
+------------------------+---------------------+
| ROW                    |                   1 |
+------------------------+---------------------+
1 row in set (0.00 sec)

确定需要变更的表没有被复制过滤。

mysql> show slave status\G
*************************** 1. row ***************************
-- 省略其他信息
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
-- 省略其他信息

确认需要变更的表存在主键或者非空的唯一键。

mysql> desc sbtest1;
+-------+-----------+------+-----+---------+----------------+
| Field | Type      | Null | Key | Default | Extra          |
+-------+-----------+------+-----+---------+----------------+
| id    | int(11)   | NO   | PRI | NULL    | auto_increment |
| k     | int(11)   | NO   | MUL | 0       |                |
| c     | char(120) | NO   |     |         |                |
| pad   | char(60)  | NO   |     |         |                |
+-------+-----------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

创建 ghost 使用的变更用户。

mysql> GRANT ALTER, CREATE, DELETE, DROP, INDEX, INSERT, LOCK TABLES, SELECT, TRIGGER, UPDATE,SUPER, REPLICATION SLAVE on *.* TO ghost@'%' identified by 'ghost';
Query OK, 0 rows affected, 1 warning (0.01 sec)

将用户和密码写入工作目录的配置文件中。

[root@10-186-61-88 ~]# cat ghost.conf 
[client]
user=ghost
password=ghost

4.3.3、开始执行更改操作

开启一个 screen，防止变更中途连接断开。

[root@10-186-61-88 ~]# screen

将变更的 alter 语句写成以下形式。

modify c varchar(200) not null default ""

执行命令开始变更，变更之前先去掉 --execute 选项模拟执行过程，查看执行中是否有问题。

[root@10-186-61-88 ~]# gh-ost --conf=ghost.conf --database=sbtest --table=sbtest1 \
--alter='modify c varchar(200) not null default ""' --max-load=Threads_running=100 \
--critical-load=Threads_running=1000 --critical-load-interval-millis=100 \
--chunk-size=100000 --throttle-control-replicas="10.186.61.101:3306" \
--max-lag-millis=1500 --host=10.186.61.101 --port=3306 --verbose  \ 
--default-retries=120 --dml-batch-size=100  \
--assume-rbr --assume-master-host=10.186.61.88 \
--panic-flag-file=/tmp/sbtest1.panic \
--postpone-cut-over-flag-file=/tmp/sbtest1.postpone \
--throttle-flag-file=/tmp/sbtest1.throttle \
--timestamp-old-table \
--serve-socket-file=/tmp/sbtest1.gh-ost.socket 

2020-07-24 15:06:28 INFO starting gh-ost 1.0.49
2020-07-24 15:06:28 INFO Migrating `sbtest`.`sbtest1`
2020-07-24 15:06:28 INFO connection validated on 10.186.61.101:3306
2020-07-24 15:06:28 INFO User has SUPER, REPLICATION SLAVE privileges, and has ALL privileges on `sbtest`.*
2020-07-24 15:06:28 INFO binary logs validated on 10.186.61.101:3306
2020-07-24 15:06:28 INFO Inspector initiated on 10-186-61-101:3306, version 5.7.29-log
2020-07-24 15:06:28 INFO Table found. Engine=InnoDB
2020-07-24 15:06:28 INFO Estimated number of rows via EXPLAIN: 4814427
2020-07-24 15:06:28 INFO Master forced to be 10.186.61.88:3306
2020-07-24 15:06:28 INFO log_slave_updates validated on 10.186.61.101:3306
2020-07-24 15:06:28 INFO connection validated on 10.186.61.101:3306
2020-07-24 15:06:28 INFO Connecting binlog streamer at mysql_bin.000008:95041262
[2020/07/24 15:06:28] [info] binlogsyncer.go:133 create BinlogSyncer with config {99999 mysql 10.186.61.101 3306 ghost    false false <nil> false UTC true 0 0s 0s 0 false}
[2020/07/24 15:06:28] [info] binlogsyncer.go:354 begin to sync binlog from position (mysql_bin.000008, 95041262)
[2020/07/24 15:06:28] [info] binlogsyncer.go:203 register slave for master server 10.186.61.101:3306
[2020/07/24 15:06:28] [info] binlogsyncer.go:723 rotate to (mysql_bin.000008, 95041262)
2020-07-24 15:06:28 INFO rotate to next log from mysql_bin.000008:0 to mysql_bin.000008
2020-07-24 15:06:28 INFO connection validated on 10.186.61.88:3306
2020-07-24 15:06:28 INFO connection validated on 10.186.61.88:3306
2020-07-24 15:06:28 INFO will use time_zone='SYSTEM' on applier
2020-07-24 15:06:28 INFO Examining table structure on applier
2020-07-24 15:06:28 INFO Applier initiated on 10-186-61-88:3306, version 5.7.29-log
2020-07-24 15:06:28 INFO Dropping table `sbtest`.`_sbtest1_ghc`
2020-07-24 15:06:28 INFO Table dropped
2020-07-24 15:06:28 INFO Creating changelog table `sbtest`.`_sbtest1_ghc`
2020-07-24 15:06:28 INFO Changelog table created
2020-07-24 15:06:28 INFO Creating ghost table `sbtest`.`_sbtest1_gho`
2020-07-24 15:06:28 INFO Ghost table created
2020-07-24 15:06:28 INFO Altering ghost table `sbtest`.`_sbtest1_gho`
2020-07-24 15:06:28 INFO Ghost table altered
2020-07-24 15:06:28 INFO Created postpone-cut-over-flag-file: /tmp/sbtest1.postpone
2020-07-24 15:06:28 INFO Waiting for ghost table to be migrated. Current lag is 0s
2020-07-24 15:06:28 INFO Intercepted changelog state GhostTableMigrated
2020-07-24 15:06:28 INFO Handled changelog state GhostTableMigrated
2020-07-24 15:06:28 INFO Chosen shared unique key is PRIMARY
2020-07-24 15:06:28 INFO Shared columns are id,k,c,pad
2020-07-24 15:06:28 INFO Listening on unix socket file: /tmp/sbtest1.gh-ost.socket
2020-07-24 15:06:28 INFO Migration min values: [1]
2020-07-24 15:06:28 INFO Migration max values: [5000000]
2020-07-24 15:06:28 INFO Waiting for first throttle metrics to be collected
2020-07-24 15:06:28 INFO First throttle metrics collected
# Migrating `sbtest`.`sbtest1`; Ghost table is `sbtest`.`_sbtest1_gho`
# Migrating 10-186-61-88:3306; inspecting 10-186-61-101:3306; executing on 10-186-61-88
# Migration started at Fri Jul 24 15:06:28 +0800 2020
# chunk-size: 100000; max-lag-millis: 1500ms; dml-batch-size: 100; max-load: Threads_running=100; critical-load: Threads_running=1000; nice-ratio: 0.000000
# throttle-flag-file: /tmp/sbtest1.throttle 
# throttle-additional-flag-file: /tmp/gh-ost.throttle 
# throttle-control-replicas count: 1
# postpone-cut-over-flag-file: /tmp/sbtest1.postpone [set]
# panic-flag-file: /tmp/sbtest1.panic
# Serving on unix socket: /tmp/sbtest1.gh-ost.socket
2020-07-24 15:06:28 INFO Row copy complete
# Migrating `sbtest`.`sbtest1`; Ghost table is `sbtest`.`_sbtest1_gho`
# Migrating 10-186-61-88:3306; inspecting 10-186-61-101:3306; executing on 10-186-61-88
# Migration started at Fri Jul 24 15:06:28 +0800 2020
# chunk-size: 100000; max-lag-millis: 1500ms; dml-batch-size: 100; max-load: Threads_running=100; critical-load: Threads_running=1000; nice-ratio: 0.000000
# throttle-flag-file: /tmp/sbtest1.throttle 
# throttle-additional-flag-file: /tmp/gh-ost.throttle 
# throttle-control-replicas count: 1
# postpone-cut-over-flag-file: /tmp/sbtest1.postpone [set]
# panic-flag-file: /tmp/sbtest1.panic
# Serving on unix socket: /tmp/sbtest1.gh-ost.socket
Copy: 0/4814427 0.0%; Applied: 0; Backlog: 0/1000; Time: 0s(total), 0s(copy); streamer: mysql_bin.000008:95044050; Lag: 0.03s, State: migrating; ETA: N/A
Copy: 0/0 100.0%; Applied: 0; Backlog: 0/1000; Time: 0s(total), 0s(copy); streamer: mysql_bin.000008:95044050; Lag: 0.03s, State: migrating; ETA: due
2020-07-24 15:06:28 INFO New table structure follows
CREATE TABLE `_sbtest1_gho` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `k` int(11) NOT NULL DEFAULT '0',
  `c` varchar(200) NOT NULL DEFAULT '',
  `pad` char(60) NOT NULL DEFAULT '',
  PRIMARY KEY (`id`),
  KEY `k_1` (`k`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
[2020/07/24 15:06:28] [info] binlogsyncer.go:164 syncer is closing...
2020-07-24 15:06:28 INFO Closed streamer connection. err=<nil>
2020-07-24 15:06:28 INFO Dropping table `sbtest`.`_sbtest1_ghc`
[2020/07/24 15:06:28] [error] binlogstreamer.go:77 close sync with err: sync is been closing...
[2020/07/24 15:06:28] [info] binlogsyncer.go:179 syncer is closed
2020-07-24 15:06:28 INFO Table dropped
2020-07-24 15:06:28 INFO Dropping table `sbtest`.`_sbtest1_gho`
2020-07-24 15:06:28 INFO Table dropped
2020-07-24 15:06:28 INFO Done migrating `sbtest`.`sbtest1`
2020-07-24 15:06:28 INFO Removing socket file: /tmp/sbtest1.gh-ost.socket
2020-07-24 15:06:28 INFO Tearing down inspector
2020-07-24 15:06:28 INFO Tearing down applier
2020-07-24 15:06:28 INFO Tearing down streamer
2020-07-24 15:06:28 INFO Tearing down throttler
# Done

确认无误后，即可开始正式的更改工作。

gh-ost --conf=ghost.conf --database=sbtest --table=sbtest1 \
--alter='modify c varchar(200) not null default ""' \
--max-load=Threads_running=100  \
--critical-load=Threads_running=1000 \
--critical-load-interval-millis=100 --chunk-size=100000 \
--throttle-control-replicas="10.186.61.101:3306" \
--max-lag-millis=1500 --host=10.186.61.101 \
--port=3306 --verbose   --default-retries=120 \
--dml-batch-size=100  --assume-rbr \
--assume-master-host=10.186.61.88 \
--panic-flag-file=/tmp/sbtest1.panic \
--postpone-cut-over-flag-file=/tmp/sbtest1.postpone \
--throttle-flag-file=/tmp/sbtest1.throttle \
--timestamp-old-table \
--serve-socket-file=/tmp/sbtest1.gh-ost.socket --execute

执行过程中会有如下的日志打印,代表的含义如下：

Copy：从原表 copy row 的进度，三列分别代表已 cpoy 的行、预估行数、进度
Applied：表示从二进制日志中读取并应用到幽灵表上的行数
Backlog：当前处理二进制日志的积压数量
Time：执行时间
streamer：当前处理到的二进制日志的位置
Lag：延时时间
State：状态（migrating：正常迁移，throttled：限流中，postponing cut-over：等待转换）
ETA：预估的完成耗时

Copy: 300000/4814427 6.2%; Applied: 0; Backlog: 0/1000; Time: 6s(total), 6s(copy); streamer: mysql_bin.000008:116441176; Lag: 1.72s, State: throttled, lag=1.824079s; ETA: 1m30s
Copy: 300000/4814427 6.2%; Applied: 0; Backlog: 0/1000; Time: 7s(total), 7s(copy); streamer: mysql_bin.000008:133260367; Lag: 1.42s, State: migrating; ETA: 1m45s

当状态成为 postponing cut-over 后，我们就可以进行下一步的转换环节，转换方式有两种，第一种是删除创建的标志文件，标志文件为 --postpone-cut-over-flag-file 选项定义的。第二种是执行交互式命令，这里我们采用第二种。

通过输出的日志，我们可以看到状态已经处于 postponing cut-over。

Copy: 5000000/5000000 100.0%; Applied: 0; Backlog: 0/1000; Time: 18m0s(total), 1m49s(copy); streamer: mysql_bin.000011:254596764; Lag: 0.02s, State: postponing cut-over; ETA: due
Copy: 5000000/5000000 100.0%; Applied: 0; Backlog: 0/1000; Time: 18m30s(total), 1m49s(copy); streamer: mysql_bin.000011:254786245; Lag: 0.02s, State: postponing cut-over; ETA: due

执行以下命令。

[root@10-186-61-88 tmp]# echo "unpostpone" |nc -U sbtest1.gh-ost.socket

查看日志输出,可以看到转换完成。

Copy: 5000000/5000000 100.0%; Applied: 0; Backlog: 0/1000; Time: 20m27s(total), 1m49s(copy); streamer: mysql_bin.000011:255529733; Lag: 0.02s, State: postponing cut-over; ETA: due
2020-07-24 15:28:53 INFO Grabbing voluntary lock: gh-ost.2088.lock
2020-07-24 15:28:53 INFO Setting LOCK timeout as 6 seconds
2020-07-24 15:28:53 INFO Looking for magic cut-over table
2020-07-24 15:28:53 INFO Creating magic cut-over table `sbtest`.`_sbtest1_20200724150824_del`
2020-07-24 15:28:53 INFO Magic cut-over table created
2020-07-24 15:28:53 INFO Locking `sbtest`.`sbtest1`, `sbtest`.`_sbtest1_20200724150824_del`
2020-07-24 15:28:53 INFO Tables locked
2020-07-24 15:28:53 INFO Session locking original & magic tables is 2088
2020-07-24 15:28:53 INFO Writing changelog state: AllEventsUpToLockProcessed:1595575733351893170
2020-07-24 15:28:53 INFO Waiting for events up to lock
2020-07-24 15:28:53 INFO Intercepted changelog state AllEventsUpToLockProcessed
2020-07-24 15:28:53 INFO Handled changelog state AllEventsUpToLockProcessed
2020-07-24 15:28:54 INFO Waiting for events up to lock: got AllEventsUpToLockProcessed:1595575733351893170
2020-07-24 15:28:54 INFO Done waiting for events up to lock; duration=696.107491ms
# Migrating `sbtest`.`sbtest1`; Ghost table is `sbtest`.`_sbtest1_gho`
# Migrating 10-186-61-88:3306; inspecting 10-186-61-101:3306; executing on 10-186-61-88
# Migration started at Fri Jul 24 15:08:24 +0800 2020
# chunk-size: 100000; max-lag-millis: 1500ms; dml-batch-size: 100; max-load: Threads_running=100; critical-load: Threads_running=1000; nice-ratio: 0.000000
# throttle-flag-file: /tmp/sbtest1.throttle 
# throttle-additional-flag-file: /tmp/gh-ost.throttle 
# throttle-control-replicas count: 1
# postpone-cut-over-flag-file: /tmp/sbtest1.postpone [set]
# panic-flag-file: /tmp/sbtest1.panic
# Serving on unix socket: /tmp/sbtest1.gh-ost.socket
Copy: 5000000/5000000 100.0%; Applied: 0; Backlog: 0/1000; Time: 20m29s(total), 1m49s(copy); streamer: mysql_bin.000011:255542872; Lag: 0.02s, State: migrating; ETA: due
2020-07-24 15:28:54 INFO Setting RENAME timeout as 3 seconds
2020-07-24 15:28:54 INFO Session renaming tables is 2084
2020-07-24 15:28:54 INFO Issuing and expecting this to block: rename /* gh-ost */ table `sbtest`.`sbtest1` to `sbtest`.`_sbtest1_20200724150824_del`, `sbtest`.`_sbtest1_gho` to `sbtest`.`sbtest1`
2020-07-24 15:28:54 INFO Found atomic RENAME to be blocking, as expected. Double checking the lock is still in place (though I don't strictly have to)
2020-07-24 15:28:54 INFO Checking session lock: gh-ost.2088.lock
2020-07-24 15:28:54 INFO Connection holding lock on original table still exists
2020-07-24 15:28:54 INFO Will now proceed to drop magic table and unlock tables
2020-07-24 15:28:54 INFO Dropping magic cut-over table
2020-07-24 15:28:54 INFO Releasing lock from `sbtest`.`sbtest1`, `sbtest`.`_sbtest1_20200724150824_del`
2020-07-24 15:28:54 INFO Tables unlocked
2020-07-24 15:28:54 INFO Tables renamed
2020-07-24 15:28:54 INFO Lock & rename duration: 721.156968ms. During this time, queries on `sbtest1` were blocked
2020-07-24 15:28:54 INFO Looking for magic cut-over table
[2020/07/24 15:28:54] [info] binlogsyncer.go:164 syncer is closing...
2020-07-24 15:28:54 INFO Closed streamer connection. err=<nil>
2020-07-24 15:28:54 INFO Dropping table `sbtest`.`_sbtest1_ghc`
[2020/07/24 15:28:54] [error] binlogstreamer.go:77 close sync with err: sync is been closing...
[2020/07/24 15:28:54] [info] binlogsyncer.go:179 syncer is closed
2020-07-24 15:28:54 INFO Table dropped
2020-07-24 15:28:54 INFO Am not dropping old table because I want this operation to be as live as possible. If you insist I should do it, please add `--ok-to-drop-table` next time. But I prefer you do not. To drop the old table, issue:
2020-07-24 15:28:54 INFO -- drop table `sbtest`.`_sbtest1_20200724150824_del`
2020-07-24 15:28:54 INFO Done migrating `sbtest`.`sbtest1`
2020-07-24 15:28:54 INFO Removing socket file: /tmp/sbtest1.gh-ost.socket
2020-07-24 15:28:54 INFO Tearing down inspector
2020-07-24 15:28:54 INFO Tearing down applier
2020-07-24 15:28:54 INFO Tearing down streamer
2020-07-24 15:28:54 INFO Tearing down throttler
# Done

登陆数据库，查看表结构是否更改。

mysql> desc sbtest1;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| k     | int(11)      | NO   | MUL | 0       |                |
| c     | varchar(200) | NO   |     |         |                |
| pad   | char(60)     | NO   |     |         |                |
+-------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

4.3.4、后续收尾工作

验证表数据是否正常
删除旧表

mysql> show tables;
+-----------------------------+
| Tables_in_sbtest            |
+-----------------------------+
| _sbtest1_20200724150824_del |
| sbtest1                     |
+-----------------------------+
2 rows in set (0.00 sec)
mysql> drop table  _sbtest1_20200724150824_del;
Query OK, 0 rows affected (0.03 sec)

清理残留的标志文件

[root@10-186-61-88 tmp]# rm sbtest1.postpone
rm: remove regular empty file ‘sbtest1.postpone’? y

参考：
https://github.com/github/gh-...

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