MySQL Utilities 高可用工具体验

MySQL Utilities是MySQL官方的工具集，其中包括高可用相关的几个工具。 以下是对当前最新版本1.6的使用体验。

前提条件

• MySQL Server 5.6+
• 基于GTID的复制
• Python 2.6+
• Connector/Python 2.0+

环境准备

在1台机器准备3个不同端口的MySQL实例用于测试

• 192.168.107.211:9001(master)
• 192.168.107.211:9002(slave1)
• 192.168.107.211:9003(slave2)

软件

• OS: CentOS 7.1
• MySQL: Percona Server 5.7.19
• Python： 2.7.5
• Connector/Python：2.1.7
• mysql-utilities：1.6.5

创建MySQL实例1

生成实例1的配置文件my1.cnf

su - mysql
vi my1.cnf
[mysqld]
port=9001
datadir=/var/lib/mysql/data1
socket=/var/lib/mysql/data1/mysql.sock
basedir=/usr/

innodb_buffer_pool_size=128M
explicit_defaults_for_timestamp
skip-name-resolve
lower-case-table-names
expire-logs-days=7
plugin-load="rpl_semi_sync_master=semisync_master.so;rpl_semi_sync_slave=semisync_slave.so"
rpl_semi_sync_master_wait_point=AFTER_SYNC
rpl_semi_sync_master_wait_no_slave=ON
rpl_semi_sync_master_enabled=ON
rpl_semi_sync_slave_enabled=ON
rpl_semi_sync_master_timeout=5000

server-id=9001
log_bin=binlog
gtid-mode=ON
enforce-gtid-consistency=ON
log-slave-updates=ON
master-info-repository=TABLE
relay-log-info-repository=TABLE
report-host=192.168.107.211

log-error=/var/lib/mysql/data1/mysqld.log
pid-file=/var/lib/mysql/data1/mysqld.pid
general-log=ON
general-log-file=/var/lib/mysql/data1/node1.log

[mysqld_safe]
pid-file=/var/lib/mysql/data1/mysqld.pid
socket=/var/lib/mysql/data1/mysql.sock
nice     = 0 

创建MySQL实例

mysqld --defaults-file=my1.cnf  --initialize-insecure
mysqld --defaults-file=my1.cnf &
mysql -S data1/mysql.sock -uroot -e "set sql_log_bin=OFF;GRANT ALL PRIVILEGES ON *.* TO 'admin'@'%' IDENTIFIED BY '12345' WITH GRANT OPTION" 

创建MySQL实例2

sed s/9001/9002/g my1.cnf | sed s/data1/data2/g >my2.cnf
mysqld --defaults-file=my2.cnf  --initialize-insecure
mysqld --defaults-file=my2.cnf &
mysql -S data2/mysql.sock -uroot -e "set sql_log_bin=OFF;GRANT ALL PRIVILEGES ON *.* TO 'admin'@'%' IDENTIFIED BY '12345' WITH GRANT OPTION" 

创建MySQL实例3

sed s/9001/9003/g my1.cnf | sed s/data1/data3/g >my3.cnf
mysqld --defaults-file=my3.cnf  --initialize-insecure
mysqld --defaults-file=my3.cnf &
mysql -S data3/mysql.sock -uroot -e "set sql_log_bin=OFF;GRANT ALL PRIVILEGES ON *.* TO 'admin'@'%' IDENTIFIED BY '12345' WITH GRANT OPTION" 

利用mysqlreplicate建立复制

-bash-4.2$ mysqlreplicate --master=admin:12345@192.168.107.211:9001 --slave=admin:12345@192.168.107.211:9002 --rpl-user=repl:repl -v
WARNING: Using a password on the command line interface can be insecure.
# master on 192.168.107.211: ... connected.
# slave on 192.168.107.211: ... connected.
# master id = 9001
#  slave id = 9002
# master uuid = b8ca6259-ab80-11e7-91fc-000c296dd240
#  slave uuid = d842240c-ab80-11e7-960f-000c296dd240
# Checking InnoDB statistics for type and version conflicts.
# Checking storage engines...
# Checking for binary logging on master...
# Setting up replication...
# Granting replication access to replication user...
# Connecting slave to master...
# CHANGE MASTER TO MASTER_HOST = '192.168.107.211', MASTER_USER = 'repl', MASTER_PASSWORD = 'repl', MASTER_PORT = 9001, MASTER_AUTO_POSITION=1
# Starting slave from master's last position...
# IO status: Waiting for master to send event
# IO thread running: Yes
# IO error: None
# SQL thread running: Yes
# SQL error: None
# ...done. 

除去各种检查，mysqlreplicate真正做的事很简单。如下

先在master上创建复制账号

CREATE USER 'repl'@'192.168.107.211' IDENTIFIED WITH 'repl'
GRANT REPLICATION SLAVE ON *.* TO 'repl'@'192.168.107.211' IDENTIFIED WITH 'repl' 

mysqlreplicate会为每个Slave创建一个复制账号，除非通过以下SQL发现该账号已经存在。

SELECT * FROM mysql.user WHERE user = 'repl' and host = '192.168.107.211' 

然后在slave上设置复制

CHANGE MASTER TO MASTER_HOST = '192.168.107.211', MASTER_USER = 'repl', MASTER_PASSWORD = 'repl', MASTER_PORT = 9001, MASTER_AUTO_POSITION=1 

在启用GTID的情况的下，从哪儿开始复制完全由GTID决定，所以mysqlreplicate中的那些和复制起始位点相关的参数，比如-b，统统被无视,其效果相当于-b。

注意:mysqlreplicate不会理会当前的复制拓扑，所以如果把master和slave对调再执行一次，就变成主主复制了。

slave1的复制配置好后，用同样的方法配置slave2的复制

mysqlreplicate --master=admin:12345@192.168.107.211:9001 --slave=admin:12345@192.168.107.211:9003 --rpl-user=repl:repl -v 

通过mysqlrplshow查看复制拓扑

-bash-4.2$ mysqlrplshow --master=admin:12345@192.168.107.211:9001 --discover-slaves-login=admin:12345 -v 
WARNING: Using a password on the command line interface can be insecure.
# master on 192.168.107.211: ... connected.
# Finding slaves for master: 192.168.107.211:9001

# Replication Topology Graph
192.168.107.211:9001 (MASTER)
   |
   +--- 192.168.107.211:9002 [IO: Yes, SQL: Yes] - (SLAVE)
   |
   +--- 192.168.107.211:9003 [IO: Yes, SQL: Yes] - (SLAVE) 

mysqlrplshow通过在master上执行SHOW SLAVE HOSTS发现初步的复制拓扑。 由于Slave停止复制或改变复制源时不能立刻反应到master的SHOW SLAVE HOSTS上，所以初步获取的复制拓扑可能存在冗余， 因此，mysqlrplshow还会再连到slave上执行SHOW SLAVE STATUS进行确认。

通过mysqlrpladmin检查集群健康状态

-bash-4.2$ mysqlrpladmin --master=admin:12345@192.168.107.211:9001 --slaves=admin:12345@192.168.107.211:9002,admin:12345@192.168.107.211:9003 health
WARNING: Using a password on the command line interface can be insecure.
# Checking privileges.
#
# Replication Topology Health:
+------------------+-------+---------+--------+------------+---------+
| host             | port  | role    | state  | gtid_mode  | health  |
+------------------+-------+---------+--------+------------+---------+
| 192.168.107.211  | 9001  | MASTER  | UP     | ON         | OK      |
| 192.168.107.211  | 9002  | SLAVE   | UP     | ON         | OK      |
| 192.168.107.211  | 9003  | SLAVE   | UP     | ON         | OK      |
+------------------+-------+---------+--------+------------+---------+
# ...done. 

通过mysqlrpladmin elect挑选合适的新主

-bash-4.2$ mysqlrpladmin --master=admin:12345@192.168.107.211:9001 --slaves=admin:12345@192.168.107.211:9002,admin:12345@192.168.107.211:9003 elect
WARNING: Using a password on the command line interface can be insecure.
# Checking privileges.
# Electing candidate slave from known slaves.
# Best slave found is located on 192.168.107.211:9002.
# ...done. 

然而，elect只是从slaves中选出第一个合格的slave，并不考虑复制是否已停止，以及哪个节点的日志更全。

下面把slave1的复制停掉

mysql -S data2/mysql.sock -uroot -e "stop slave" 

再在master执行一条SQL

mysql -S data1/mysql.sock -uroot -e "create database test" 

现在slave1上少了一个事务

-bash-4.2$ mysqlrpladmin --master=admin:12345@192.168.107.211:9001 --slaves=admin:12345@192.168.107.211:9002,admin:12345@192.168.107.211:9003 gtid
WARNING: Using a password on the command line interface can be insecure.
# Checking privileges.
#
# UUIDS for all servers:
+------------------+-------+---------+---------------------------------------+
| host             | port  | role    | uuid                                  |
+------------------+-------+---------+---------------------------------------+
| 192.168.107.211  | 9001  | MASTER  | 5daf1e10-ac41-11e7-bcc4-000c296dd240  |
| 192.168.107.211  | 9002  | SLAVE   | fe084f45-ac43-11e7-a343-000c296dd240  |
| 192.168.107.211  | 9003  | SLAVE   | d0af3a6a-ac41-11e7-85e0-000c296dd240  |
+------------------+-------+---------+---------------------------------------+
#
# Transactions executed on the server:
+------------------+-------+---------+-------------------------------------------+
| host             | port  | role    | gtid                                      |
+------------------+-------+---------+-------------------------------------------+
| 192.168.107.211  | 9001  | MASTER  | 5daf1e10-ac41-11e7-bcc4-000c296dd240:1-3  |
| 192.168.107.211  | 9002  | SLAVE   | 5daf1e10-ac41-11e7-bcc4-000c296dd240:1-2  |
| 192.168.107.211  | 9003  | SLAVE   | 5daf1e10-ac41-11e7-bcc4-000c296dd240:1-3  |
+------------------+-------+---------+-------------------------------------------+
# ...done. 

但elect仍然会选slave1

-bash-4.2$ mysqlrpladmin --master=admin:12345@192.168.107.211:9001 --slaves=admin:12345@192.168.107.211:9002,admin:12345@192.168.107.211:9003 elect
WARNING: Using a password on the command line interface can be insecure.
# Checking privileges.
# Electing candidate slave from known slaves.
# Best slave found is located on 192.168.107.211:9002.
# ...done. 

通过mysqlrpladmin switchover在线切换主备

-bash-4.2$ mysqlrpladmin --master=admin:12345@192.168.107.211:9001 --slaves=admin:12345@192.168.107.211:9002,admin:12345@192.168.107.211:9003 --new-master=admin:12345@192.168.107.211:9002 switchover
WARNING: Using a password on the command line interface can be insecure.
# Checking privileges.
# Performing switchover from master at 192.168.107.211:9001 to slave at 192.168.107.211:9002.
# Checking candidate slave prerequisites.
# Checking slaves configuration to master.
# Waiting for slaves to catch up to old master.
Slave 192.168.107.211:9002 did not catch up to the master.
ERROR: Slave 192.168.107.211:9002 did not catch up to the master. 

switchover会连接到每一个节点并等待所有slave回放完日志才执行切换，因此有任何一个节点故障或任何一个slave复制故障都不会执行switchover。

启动刚才停掉的slave1的复制

mysql -S data2/mysql.sock -uroot -e "start slave" 

再次执行switchover，成功

-bash-4.2$ mysqlrpladmin --master=admin:12345@192.168.107.211:9001 --slaves=admin:12345@192.168.107.211:9002,admin:12345@192.168.107.211:9003 --new-master=admin:12345@192.168.107.211:9002 --demote-master switchover
WARNING: Using a password on the command line interface can be insecure.
# Checking privileges.
# Performing switchover from master at 192.168.107.211:9001 to slave at 192.168.107.211:9002.
# Checking candidate slave prerequisites.
# Checking slaves configuration to master.
# Waiting for slaves to catch up to old master.
# Stopping slaves.
# Performing STOP on all slaves.
# Demoting old master to be a slave to the new master.
# Switching slaves to new master.
# Starting all slaves.
# Performing START on all slaves.
# Checking slaves for errors.
# Switchover complete.
#
# Replication Topology Health:
+------------------+-------+---------+--------+------------+---------+
| host             | port  | role    | state  | gtid_mode  | health  |
+------------------+-------+---------+--------+------------+---------+
| 192.168.107.211  | 9002  | MASTER  | UP     | ON         | OK      |
| 192.168.107.211  | 9001  | SLAVE   | UP     | ON         | OK      |
| 192.168.107.211  | 9003  | SLAVE   | UP     | ON         | OK      |
+------------------+-------+---------+--------+------------+---------+
# ...done. 

执行switchover时，有一段Waiting for slaves to catch up to old master.，如果任何一个slave有故障无法同步到和master相同的状态，switchover会失败。即switchover的前提条件是所有节点（包括master和所有salve）都是OK的。

通过mysqlrpladmin failover故障切换主备

-bash-4.2$ mysqlrpladmin --slaves=admin:12345@192.168.107.211:9001,admin:12345@192.168.107.211:9003 failover
WARNING: Using a password on the command line interface can be insecure.
# Checking privileges.
# Performing failover.
# Candidate slave 192.168.107.211:9001 will become the new master.
# Checking slaves status (before failover).
# Preparing candidate for failover.
# Creating replication user if it does not exist.
# Stopping slaves.
# Performing STOP on all slaves.
# Switching slaves to new master.
# Disconnecting new master as slave.
# Starting slaves.
# Performing START on all slaves.
# Checking slaves for errors.
# Failover complete.
#
# Replication Topology Health:
+------------------+-------+---------+--------+------------+---------+
| host             | port  | role    | state  | gtid_mode  | health  |
+------------------+-------+---------+--------+------------+---------+
| 192.168.107.211  | 9001  | MASTER  | UP     | ON         | OK      |
| 192.168.107.211  | 9003  | SLAVE   | UP     | ON         | OK      |
+------------------+-------+---------+--------+------------+---------+
# ...done. 

failover时要求所有slave的SQL线程都是正常的，IO线程可以停止或异常。 如果未指定--candidates，一般会以slaves中第1个slave作为新主。 如果新主的binlog不是最新的，会先向拥有最新日志的slave复制，并等到binlog追平了再切换。

小结

从上面操作过程来看，借助MySQL Utilities管理MySQL集群还比较简便，但结合代码考虑到各种场景，这套工具和MHA比起来还不够严谨。

1. 没有把从库的READ_ONLY设置集成到脚本里
2. switchover时没有终止运行中的事务，实际也没有有效的手段阻止新的写事务在旧master上执行。
3. failover不检查master死活，需要DBA在调用failover前自己检查，否则会引起脑裂。