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MySQL 5.6版本引入GTID来解决主从切换时BINLOG位置点难定位的问题，MHA从0.56版本开始支持基于GTID的复制，在发生故障切换时判断群集是否能采用基于GTID的方式进行切换
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基于GTID进行故障切换的条件：1、所有节点开启GTID模式，设置gtid_mode=12、所有节点上Executed_Gtid_Set不为空3、至少一个节点使用Auto_Position=1##==========================================##基于GTID进行故障切换：1、如果候选Master节点不拥有最新的Relay log，那么将候选Master连接到拥有最新Relay log的Salve上进行日志补偿2、如果群集中使用Binlog Server，则尝试从Binlog Server上拉取缺失的Binlog并应用到候选Master上3、候选Matser拥有最新数据，将其升级为新Master，将其他slave连接到新Master上进行数据同步，可以给masterha_master_switch传入–wait_until_gtid_in_sync=1参数使其不等其它Slave完成数据同步，以加快切换速度。##==========================================##基于GTID模式进行故障切换时，无论原Master节点OS是否正常，都不会尝试从原Master节点读取BINLOG进行日志补偿。基于GTID模式的MHA支持在复制拓扑中使用BINLOG Server来进行日志补偿，而非GTID模式的MHA会忽略BINLOG Server。建议在基于GTID模式的群集中，不使用MHA进行"手动主从切换"，该操作可能会导致原主库上部分BINLOG丢失。##==========================================##在非GTID模式下，会先进行Phase 3.1阶段，从拥有最新BINLOG的从库上获取差异日志，再进行Phase 3.2阶段，尝试从原Master服务器上获取最新BINLOG。
使用非GTID模式切换的日志
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在基于GTID模式下，不会进行Phase 3.2阶段，即尝试从原Master服务器中获取最新BINLOG。
使用GTID模式切换的日志：
Sun Jul 8 23:35:21 2018 - [info] MHA::MasterMonitor version 0.56.Sun Jul 8 23:35:21 2018 - [info] GTID failover mode = 1Sun Jul 8 23:35:21 2018 - [info] Dead Servers:Sun Jul 8 23:35:21 2018 - [info] Alive Servers:Sun Jul 8 23:35:21 2018 - [info] 10.0.203.104(10.0.203.104:3358)Sun Jul 8 23:35:21 2018 - [info] 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:35:21 2018 - [info] 10.0.203.117(10.0.203.117:3358)Sun Jul 8 23:35:21 2018 - [info] Alive Slaves:Sun Jul 8 23:35:21 2018 - [info] 10.0.203.104(10.0.203.104:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:35:21 2018 - [info] GTID ONSun Jul 8 23:35:21 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:35:21 2018 - [info] Primary candidate for the new Master (candidate_master is set)Sun Jul 8 23:35:21 2018 - [info] 10.0.203.117(10.0.203.117:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:35:21 2018 - [info] GTID ONSun Jul 8 23:35:21 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:35:21 2018 - [info] Current Alive Master: 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:35:21 2018 - [info] Checking slave configurations..Sun Jul 8 23:35:21 2018 - [info] read_only=1 is not set on slave 10.0.203.104(10.0.203.104:3358).Sun Jul 8 23:35:21 2018 - [info] read_only=1 is not set on slave 10.0.203.117(10.0.203.117:3358).Sun Jul 8 23:35:21 2018 - [info] Checking replication filtering settings..Sun Jul 8 23:35:21 2018 - [info] binlog_do_db= , binlog_ignore_db= Sun Jul 8 23:35:21 2018 - [info] Replication filtering check ok.Sun Jul 8 23:35:21 2018 - [info] GTID (with auto-pos) is supported. Skipping all SSH and Node package checking.Sun Jul 8 23:35:21 2018 - [info] Checking SSH publickey authentication settings on the current master..Sun Jul 8 23:35:22 2018 - [info] HealthCheck: SSH to 10.0.203.109 is reachable.Sun Jul 8 23:35:22 2018 - [info] 10.0.203.109(10.0.203.109:3358) (current master) +--10.0.203.104(10.0.203.104:3358) +--10.0.203.117(10.0.203.117:3358)Sun Jul 8 23:35:22 2018 - [warning] master_ip_failover_script is not defined.Sun Jul 8 23:35:22 2018 - [warning] shutdown_script is not defined.Sun Jul 8 23:35:22 2018 - [info] Set master ping interval 1 seconds.Sun Jul 8 23:35:22 2018 - [warning] secondary_check_script is not defined. It is highly recommended setting it to check master reachability from two or more routes.Sun Jul 8 23:35:22 2018 - [info] Starting ping health check on 10.0.203.109(10.0.203.109:3358)..Sun Jul 8 23:35:22 2018 - [info] Ping(SELECT) succeeded, waiting until MySQL doesn't respond..Sun Jul 8 23:35:58 2018 - [warning] Got error on MySQL select ping: 2006 (MySQL server has gone away)Sun Jul 8 23:35:58 2018 - [info] Executing SSH check script: exit 0Sun Jul 8 23:35:58 2018 - [info] HealthCheck: SSH to 10.0.203.109 is reachable.Sun Jul 8 23:35:59 2018 - [warning] Got error on MySQL connect: 2013 (Lost connection to MySQL server at 'reading initial communication packet', system error: 111)Sun Jul 8 23:35:59 2018 - [warning] Connection failed 2 time(s)..Sun Jul 8 23:36:00 2018 - [warning] Got error on MySQL connect: 2013 (Lost connection to MySQL server at 'reading initial communication packet', system error: 111)Sun Jul 8 23:36:00 2018 - [warning] Connection failed 3 time(s)..Sun Jul 8 23:36:01 2018 - [warning] Got error on MySQL connect: 2013 (Lost connection to MySQL server at 'reading initial communication packet', system error: 111)Sun Jul 8 23:36:01 2018 - [warning] Connection failed 4 time(s)..Sun Jul 8 23:36:01 2018 - [warning] Master is not reachable from health checker!Sun Jul 8 23:36:01 2018 - [warning] Master 10.0.203.109(10.0.203.109:3358) is not reachable!Sun Jul 8 23:36:01 2018 - [warning] SSH is reachable.Sun Jul 8 23:36:01 2018 - [info] Connecting to a master server failed. Reading configuration file /etc/masterha_default.cnf and /etc/masterha/app1.cnf again, and trying to connect to all servers to check server status..Sun Jul 8 23:36:01 2018 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.Sun Jul 8 23:36:01 2018 - [info] Reading application default configuration from /etc/masterha/app1.cnf..Sun Jul 8 23:36:01 2018 - [info] Reading server configuration from /etc/masterha/app1.cnf..Sun Jul 8 23:36:01 2018 - [info] GTID failover mode = 1Sun Jul 8 23:36:01 2018 - [info] Dead Servers:Sun Jul 8 23:36:01 2018 - [info] 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Alive Servers:Sun Jul 8 23:36:01 2018 - [info] 10.0.203.104(10.0.203.104:3358)Sun Jul 8 23:36:01 2018 - [info] 10.0.203.117(10.0.203.117:3358)Sun Jul 8 23:36:01 2018 - [info] Alive Slaves:Sun Jul 8 23:36:01 2018 - [info] 10.0.203.104(10.0.203.104:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Primary candidate for the new Master (candidate_master is set)Sun Jul 8 23:36:01 2018 - [info] 10.0.203.117(10.0.203.117:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Checking slave configurations..Sun Jul 8 23:36:01 2018 - [info] read_only=1 is not set on slave 10.0.203.104(10.0.203.104:3358).Sun Jul 8 23:36:01 2018 - [info] read_only=1 is not set on slave 10.0.203.117(10.0.203.117:3358).Sun Jul 8 23:36:01 2018 - [info] Checking replication filtering settings..Sun Jul 8 23:36:01 2018 - [info] Replication filtering check ok.Sun Jul 8 23:36:01 2018 - [info] Master is down!Sun Jul 8 23:36:01 2018 - [info] Terminating monitoring script.Sun Jul 8 23:36:01 2018 - [info] Got exit code 20 (Master dead).Sun Jul 8 23:36:01 2018 - [info] MHA::MasterFailover version 0.56.Sun Jul 8 23:36:01 2018 - [info] Starting master failover.Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 1: Configuration Check Phase..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] GTID failover mode = 1Sun Jul 8 23:36:01 2018 - [info] Dead Servers:Sun Jul 8 23:36:01 2018 - [info] 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Checking master reachability via MySQL(double check)...Sun Jul 8 23:36:01 2018 - [info] ok.Sun Jul 8 23:36:01 2018 - [info] Alive Servers:Sun Jul 8 23:36:01 2018 - [info] 10.0.203.104(10.0.203.104:3358)Sun Jul 8 23:36:01 2018 - [info] 10.0.203.117(10.0.203.117:3358)Sun Jul 8 23:36:01 2018 - [info] Alive Slaves:Sun Jul 8 23:36:01 2018 - [info] 10.0.203.104(10.0.203.104:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Primary candidate for the new Master (candidate_master is set)Sun Jul 8 23:36:01 2018 - [info] 10.0.203.117(10.0.203.117:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Starting GTID based failover.Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] ** Phase 1: Configuration Check Phase completed.Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 2: Dead Master Shutdown Phase..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] Forcing shutdown so that applications never connect to the current master..Sun Jul 8 23:36:01 2018 - [warning] master_ip_failover_script is not set. Skipping invalidating dead master IP address.Sun Jul 8 23:36:01 2018 - [warning] shutdown_script is not set. Skipping explicit shutting down of the dead master.Sun Jul 8 23:36:01 2018 - [info] * Phase 2: Dead Master Shutdown Phase completed.Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 3: Master Recovery Phase..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 3.1: Getting Latest Slaves Phase..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] The latest binary log file/position on all slaves is mysql-bin.000008:6689Sun Jul 8 23:36:01 2018 - [info] Retrieved Gtid Set: 541e0f07-8047-11e8-8434-0800270b00d2:49-69Sun Jul 8 23:36:01 2018 - [info] Latest slaves (Slaves that received relay log files to the latest):Sun Jul 8 23:36:01 2018 - [info] 10.0.203.104(10.0.203.104:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Primary candidate for the new Master (candidate_master is set)Sun Jul 8 23:36:01 2018 - [info] 10.0.203.117(10.0.203.117:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] The oldest binary log file/position on all slaves is mysql-bin.000008:6689Sun Jul 8 23:36:01 2018 - [info] Retrieved Gtid Set: 541e0f07-8047-11e8-8434-0800270b00d2:49-69Sun Jul 8 23:36:01 2018 - [info] Oldest slaves:Sun Jul 8 23:36:01 2018 - [info] 10.0.203.104(10.0.203.104:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Primary candidate for the new Master (candidate_master is set)Sun Jul 8 23:36:01 2018 - [info] 10.0.203.117(10.0.203.117:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 3.3: Determining New Master Phase..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] Searching new master from slaves..Sun Jul 8 23:36:01 2018 - [info] Candidate masters from the configuration file:Sun Jul 8 23:36:01 2018 - [info] 10.0.203.104(10.0.203.104:3358) Version=5.7.19-log (oldest major version between slaves) log-bin:enabledSun Jul 8 23:36:01 2018 - [info] GTID ONSun Jul 8 23:36:01 2018 - [info] Replicating from 10.0.203.109(10.0.203.109:3358)Sun Jul 8 23:36:01 2018 - [info] Primary candidate for the new Master (candidate_master is set)Sun Jul 8 23:36:01 2018 - [info] Non-candidate masters:Sun Jul 8 23:36:01 2018 - [info] Searching from candidate_master slaves which have received the latest relay log events..Sun Jul 8 23:36:01 2018 - [info] New master is 10.0.203.104(10.0.203.104:3358)Sun Jul 8 23:36:01 2018 - [info] Starting master failover..Sun Jul 8 23:36:01 2018 - [info] From:10.0.203.109(10.0.203.109:3358) (current master) +--10.0.203.104(10.0.203.104:3358) +--10.0.203.117(10.0.203.117:3358)To:10.0.203.104(10.0.203.104:3358) (new master) +--10.0.203.117(10.0.203.117:3358)Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 3.3: New Master Recovery Phase..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] Waiting all logs to be applied.. Sun Jul 8 23:36:01 2018 - [info] done.Sun Jul 8 23:36:01 2018 - [info] Getting new master's binlog name and position..Sun Jul 8 23:36:01 2018 - [info] mysql-bin.000006:77499Sun Jul 8 23:36:01 2018 - [info] All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_HOST='10.0.203.104', MASTER_PORT=3358, MASTER_AUTO_POSITION=1, MASTER_USER='replicater', MASTER_PASSWORD='xxx';Sun Jul 8 23:36:01 2018 - [info] Master Recovery succeeded. File:Pos:Exec_Gtid_Set: mysql-bin.000006, 77499, 41d8a420-8047-11e8-8580-080027e837eb:1-92,541e0f07-8047-11e8-8434-0800270b00d2:1-69Sun Jul 8 23:36:01 2018 - [warning] master_ip_failover_script is not set. Skipping taking over new master IP address.Sun Jul 8 23:36:01 2018 - [info] ** Finished master recovery successfully.Sun Jul 8 23:36:01 2018 - [info] * Phase 3: Master Recovery Phase completed.Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 4: Slaves Recovery Phase..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 4.1: Starting Slaves in parallel..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] -- Slave recovery on host 10.0.203.117(10.0.203.117:3358) started, pid: 5680. Check tmp log /var/log/masterha/app1/10.0.203.117_3358_20180708233601.log if it takes time..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] Log messages from 10.0.203.117 ...Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] Resetting slave 10.0.203.117(10.0.203.117:3358) and starting replication from the new master 10.0.203.104(10.0.203.104:3358)..Sun Jul 8 23:36:01 2018 - [info] Executed CHANGE MASTER.Sun Jul 8 23:36:01 2018 - [info] Slave started.Sun Jul 8 23:36:01 2018 - [info] gtid_wait(41d8a420-8047-11e8-8580-080027e837eb:1-92,541e0f07-8047-11e8-8434-0800270b00d2:1-69) completed on 10.0.203.117(10.0.203.117:3358). Executed 0 events.Sun Jul 8 23:36:01 2018 - [info] End of log messages from 10.0.203.117.Sun Jul 8 23:36:01 2018 - [info] -- Slave on host 10.0.203.117(10.0.203.117:3358) started.Sun Jul 8 23:36:01 2018 - [info] All new slave servers recovered successfully.Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] * Phase 5: New master cleanup phase..Sun Jul 8 23:36:01 2018 - [info] Sun Jul 8 23:36:01 2018 - [info] Resetting slave info on the new master..Sun Jul 8 23:36:01 2018 - [info] 10.0.203.104: Resetting slave info succeeded.Sun Jul 8 23:36:01 2018 - [info] Master failover to 10.0.203.104(10.0.203.104:3358) completed successfully.Sun Jul 8 23:36:01 2018 - [info] ----- Failover Report -----app1: MySQL Master failover 10.0.203.109(10.0.203.109:3358) to 10.0.203.104(10.0.203.104:3358) succeededMaster 10.0.203.109(10.0.203.109:3358) is down!Check MHA Manager logs at localhost.localdomain:/var/log/masterha/app1/manager.log for details.Started automated(non-interactive) failover.Selected 10.0.203.104(10.0.203.104:3358) as a new master.10.0.203.104(10.0.203.104:3358): OK: Applying all logs succeeded.10.0.203.117(10.0.203.117:3358): OK: Slave started, replicating from 10.0.203.104(10.0.203.104:3358)10.0.203.104(10.0.203.104:3358): Resetting slave info succeeded.Master failover to 10.0.203.104(10.0.203.104:3358) completed successfully.
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MHA在检查时，使用SHOW SLAVE STATUS获取结构中Auto_Position的值来判断是否使用master_auto_position参数来搭建主从复制。MHA在切换时，如果使用非GTID模式切换，则在CHANGE MASTER中不会带上参数master_auto_position=0，而如果该从库之前配置为master_auto_position=1，那么CHANGE MASTER会报错，无法正常进行切换。
因此不能简单修改Server.PM或DBHelper.pm文件来将基于GTID模式切换的群集修改为使用非GTID模式进行切换。
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如果群集因为某种原因导致主从节点上的Executed_Gtid_Set不同，如：
1、对从库进行直接授权，导致从库比主库拥有更多BINLOG，但该Binlog因各种原因被Purged掉
2、群集做过版本升级，从未使用GTID的版本升级到GTID版本，从库上曾一段时间内作为主库提供服务，但该时间段日志被Purged掉
有上诉类似问题时，将从库提升为主库并使用master_auto_position=1来配置复制，复制会因为新主库无法提供足够BINLOG事件而失败。
处理办法：
1、通过RESET MASTER和SET GLOBAL gtid_purged=''使得所有节点拥有相同的GTID 集合
2、将所有复制修改为基于POS点搭建的复制。
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