目录

前言

核心流程函数调用路径

GetReplicationAnalysis

故障类型和对应的处理函数

​编辑

拓扑结构警告类型

核心流程总结

与MHA相比

前言

Orchestrator另外一个重要的功能是监控集群，发现故障。根据从复制拓扑本身获得的信息，它可以识别各种故障场景。

核心流程函数调用路径

ContinuousDiscovery
--> CheckAndRecover // 检查恢复的入口函数
--> GetReplicationAnalysis  // 查询SQL，根据实例的状态确定故障或者警告类型。检查复制问题  (dead master; unreachable master; 等)
--> executeCheckAndRecoverFunction  // 根据分析结果选择正确的检查和恢复函数。然后会同步执行该函数。
--> getCheckAndRecoverFunction // 根据分析结果选择正确的检查和恢复函数。然后会同步执行该函数。
--> runEmergentOperations // 
--> checkAndExecuteFailureDetectionProcesses //   尝试往数据库中插入这个故障发现记录，然后执行故障发现阶段所需的操作，执行 OnFailureDetectionProcesses （故障发现阶段的）钩子脚本
--> AttemptFailureDetectionRegistration //  尝试往数据库中插入故障发现记录 ，如果失败 意味着这个问题可能已经被发现了，
--> checkAndRecoverDeadMaster  // 根据故障情况 执行恢复，这里选择DeadMaster 故障类型举例 
--> AttemptRecoveryRegistration // 尝试往数据库中插入一条恢复记录；如果这一尝试失败，那么意味着恢复已经在进行中。
--> recoverDeadMaster //  用于恢复DeadMaster故障类型的函数，其中包含了完整的逻辑。会执行PreFailoverProcesses 钩子脚本

GetReplicationAnalysis

该函数将检查复制问题 (dead master; unreachable master; 等），根据实例的状态确定故障或者警告类型。

该函数会运行一个复杂SQL ,该SQL会每秒执行一次 ，执行间隔是由定时器 recoveryTick决定 ，SQL中已经进行了一部分逻辑处理，并将数据存储到 ReplicationAnalysis 结构体中，

SELECT
		master_instance.hostname,
		master_instance.port,
		master_instance.read_only AS read_only,
		MIN(master_instance.data_center) AS data_center,
		MIN(master_instance.region) AS region,
		MIN(master_instance.physical_environment) AS physical_environment,
		MIN(master_instance.master_host) AS master_host,
		MIN(master_instance.master_port) AS master_port,
		MIN(master_instance.cluster_name) AS cluster_name,
		MIN(master_instance.binary_log_file) AS binary_log_file,
		MIN(master_instance.binary_log_pos) AS binary_log_pos,
		MIN(
			IFNULL(
				master_instance.binary_log_file = database_instance_stale_binlog_coordinates.binary_log_file
				AND master_instance.binary_log_pos = database_instance_stale_binlog_coordinates.binary_log_pos
				AND database_instance_stale_binlog_coordinates.first_seen < NOW() - interval 10 second,
				0
			)
		) AS is_stale_binlog_coordinates,
		MIN(
			IFNULL(
				cluster_alias.alias,
				master_instance.cluster_name
			)
		) AS cluster_alias,
		MIN(
			IFNULL(
				cluster_domain_name.domain_name,
				master_instance.cluster_name
			)
		) AS cluster_domain,
		MIN(
			master_instance.last_checked <= master_instance.last_seen
			and master_instance.last_attempted_check <= master_instance.last_seen + interval 6 second
		) = 1 AS is_last_check_valid,
		/* To be considered a master, traditional async replication must not be present/valid AND the host should either */
		/* not be a replication group member OR be the primary of the replication group */
		MIN(master_instance.last_check_partial_success) as last_check_partial_success,
		MIN(
			(
				master_instance.master_host IN ('', '_')
				OR master_instance.master_port = 0
				OR substr(master_instance.master_host, 1, 2) = '//'
			)
			AND (
				master_instance.replication_group_name = ''
				OR master_instance.replication_group_member_role = 'PRIMARY'
			)
		) AS is_master,
		MIN(
			master_instance.replication_group_name != ''
			AND master_instance.replication_group_member_state != 'OFFLINE'
		) AS is_replication_group_member,
		MIN(master_instance.is_co_master) AS is_co_master,
		MIN(
			CONCAT(
				master_instance.hostname,
				':',
				master_instance.port
			) = master_instance.cluster_name
		) AS is_cluster_master,
		MIN(master_instance.gtid_mode) AS gtid_mode,
		COUNT(replica_instance.server_id) AS count_replicas,
		IFNULL(
			SUM(
				replica_instance.last_checked <= replica_instance.last_seen
			),
			0
		) AS count_valid_replicas,
		IFNULL(
			SUM(
				replica_instance.last_checked <= replica_instance.last_seen
				AND replica_instance.slave_io_running != 0
				AND replica_instance.slave_sql_running != 0
			),
			0
		) AS count_valid_replicating_replicas,
		IFNULL(
			SUM(
				replica_instance.last_checked <= replica_instance.last_seen
				AND replica_instance.slave_io_running = 0
				AND replica_instance.last_io_error like '%error %connecting to master%'
				AND replica_instance.slave_sql_running = 1
			),
			0
		) AS count_replicas_failing_to_connect_to_master,
		MIN(master_instance.replication_depth) AS replication_depth,
		GROUP_CONCAT(
			concat(
				replica_instance.Hostname,
				':',
				replica_instance.Port
			)
		) as slave_hosts,
		MIN(
			master_instance.slave_sql_running = 1
			AND master_instance.slave_io_running = 0
			AND master_instance.last_io_error like '%error %connecting to master%'
		) AS is_failing_to_connect_to_master,
		MIN(
			master_downtime.downtime_active is not null
			and ifnull(master_downtime.end_timestamp, now()) > now()
		) AS is_downtimed,
		MIN(
			IFNULL(master_downtime.end_timestamp, '')
		) AS downtime_end_timestamp,
		MIN(
			IFNULL(
				unix_timestamp() - unix_timestamp(master_downtime.end_timestamp),
				0
			)
		) AS downtime_remaining_seconds,
		MIN(
			master_instance.binlog_server
		) AS is_binlog_server,
		MIN(master_instance.pseudo_gtid) AS is_pseudo_gtid,
		MIN(
			master_instance.supports_oracle_gtid
		) AS supports_oracle_gtid,
		MIN(
			master_instance.semi_sync_master_enabled
		) AS semi_sync_master_enabled,
		MIN(
			master_instance.semi_sync_master_wait_for_slave_count
		) AS semi_sync_master_wait_for_slave_count,
		MIN(
			master_instance.semi_sync_master_clients
		) AS semi_sync_master_clients,
		MIN(
			master_instance.semi_sync_master_status
		) AS semi_sync_master_status,
		SUM(replica_instance.is_co_master) AS count_co_master_replicas,
		SUM(replica_instance.oracle_gtid) AS count_oracle_gtid_replicas,
		IFNULL(
			SUM(
				replica_instance.last_checked <= replica_instance.last_seen
				AND replica_instance.oracle_gtid != 0
			),
			0
		) AS count_valid_oracle_gtid_replicas,
		SUM(
			replica_instance.binlog_server
		) AS count_binlog_server_replicas,
		IFNULL(
			SUM(
				replica_instance.last_checked <= replica_instance.last_seen
				AND replica_instance.binlog_server != 0
			),
			0
		) AS count_valid_binlog_server_replicas,
		SUM(
			replica_instance.semi_sync_replica_enabled
		) AS count_semi_sync_replicas,
		IFNULL(
			SUM(
				replica_instance.last_checked <= replica_instance.last_seen
				AND replica_instance.semi_sync_replica_enabled != 0
			),
			0
		) AS count_valid_semi_sync_replicas,
		MIN(
			master_instance.mariadb_gtid
		) AS is_mariadb_gtid,
		SUM(replica_instance.mariadb_gtid) AS count_mariadb_gtid_replicas,
		IFNULL(
			SUM(
				replica_instance.last_checked <= replica_instance.last_seen
				AND replica_instance.mariadb_gtid != 0
			),
			0
		) AS count_valid_mariadb_gtid_replicas,
		IFNULL(
			SUM(
				replica_instance.log_bin
				AND replica_instance.log_slave_updates
			),
			0
		) AS count_logging_replicas,
		IFNULL(
			SUM(
				replica_instance.log_bin
				AND replica_instance.log_slave_updates
				AND replica_instance.binlog_format = 'STATEMENT'
			),
			0
		) AS count_statement_based_logging_replicas,
		IFNULL(
			SUM(
				replica_instance.log_bin
				AND replica_instance.log_slave_updates
				AND replica_instance.binlog_format = 'MIXED'
			),
			0
		) AS count_mixed_based_logging_replicas,
		IFNULL(
			SUM(
				replica_instance.log_bin
				AND replica_instance.log_slave_updates
				AND replica_instance.binlog_format = 'ROW'
			),
			0
		) AS count_row_based_logging_replicas,
		IFNULL(
			SUM(replica_instance.sql_delay > 0),
			0
		) AS count_delayed_replicas,
		IFNULL(
			SUM(replica_instance.slave_lag_seconds > 10),
			0
		) AS count_lagging_replicas,
		IFNULL(MIN(replica_instance.gtid_mode), '') AS min_replica_gtid_mode,
		IFNULL(MAX(replica_instance.gtid_mode), '') AS max_replica_gtid_mode,
		IFNULL(
			MAX(
				case when replica_downtime.downtime_active is not null
				and ifnull(replica_downtime.end_timestamp, now()) > now() then '' else replica_instance.gtid_errant end
			),
			''
		) AS max_replica_gtid_errant,
		IFNULL(
			SUM(
				replica_downtime.downtime_active is not null
				and ifnull(replica_downtime.end_timestamp, now()) > now()
			),
			0
		) AS count_downtimed_replicas,
		COUNT(
			DISTINCT case when replica_instance.log_bin
			AND replica_instance.log_slave_updates then replica_instance.major_version else NULL end
		) AS count_distinct_logging_major_versions
	FROM
		database_instance master_instance
		LEFT JOIN hostname_resolve ON (
			master_instance.hostname = hostname_resolve.hostname
		)
		LEFT JOIN database_instance replica_instance ON (
			COALESCE(
				hostname_resolve.resolved_hostname,
				master_instance.hostname
			) = replica_instance.master_host
			AND master_instance.port = replica_instance.master_port
		)
		LEFT JOIN database_instance_maintenance ON (
			master_instance.hostname = database_instance_maintenance.hostname
			AND master_instance.port = database_instance_maintenance.port
			AND database_instance_maintenance.maintenance_active = 1
		)
		LEFT JOIN database_instance_stale_binlog_coordinates ON (
			master_instance.hostname = database_instance_stale_binlog_coordinates.hostname
			AND master_instance.port = database_instance_stale_binlog_coordinates.port
		)
		LEFT JOIN database_instance_downtime as master_downtime ON (
			master_instance.hostname = master_downtime.hostname
			AND master_instance.port = master_downtime.port
			AND master_downtime.downtime_active = 1
		)
		LEFT JOIN database_instance_downtime as replica_downtime ON (
			replica_instance.hostname = replica_downtime.hostname
			AND replica_instance.port = replica_downtime.port
			AND replica_downtime.downtime_active = 1
		)
		LEFT JOIN cluster_alias ON (
			cluster_alias.cluster_name = master_instance.cluster_name
		)
		LEFT JOIN cluster_domain_name ON (
			cluster_domain_name.cluster_name = master_instance.cluster_name
		)
	WHERE
		database_instance_maintenance.database_instance_maintenance_id IS NULL
		AND '' IN ('', master_instance.cluster_name)
	GROUP BY
		master_instance.hostname,
		master_instance.port
			HAVING
				(
					MIN(
						master_instance.last_checked <= master_instance.last_seen
						and master_instance.last_attempted_check <= master_instance.last_seen + interval 6 second
					) = 1
					/* AS is_last_check_valid */
				) = 0
				OR (
					IFNULL(
						SUM(
							replica_instance.last_checked <= replica_instance.last_seen
							AND replica_instance.slave_io_running = 0
							AND replica_instance.last_io_error like '%error %connecting to master%'
							AND replica_instance.slave_sql_running = 1
						),
						0
					)
					/* AS count_replicas_failing_to_connect_to_master */
					> 0
				)
				OR (
					IFNULL(
						SUM(
							replica_instance.last_checked <= replica_instance.last_seen
						),
						0
					)
					/* AS count_valid_replicas */
					< COUNT(replica_instance.server_id)
					/* AS count_replicas */
				)
				OR (
					IFNULL(
						SUM(
							replica_instance.last_checked <= replica_instance.last_seen
							AND replica_instance.slave_io_running != 0
							AND replica_instance.slave_sql_running != 0
						),
						0
					)
					/* AS count_valid_replicating_replicas */
					< COUNT(replica_instance.server_id)
					/* AS count_replicas */
				)
				OR (
					MIN(
						master_instance.slave_sql_running = 1
						AND master_instance.slave_io_running = 0
						AND master_instance.last_io_error like '%error %connecting to master%'
					)
					/* AS is_failing_to_connect_to_master */
				)
				OR (
					COUNT(replica_instance.server_id)
					/* AS count_replicas */
					> 0
				)
	ORDER BY
		is_master DESC,
		is_cluster_master DESC,
		count_replicas DESC\G

故障类型和对应的处理函数

主要根据结构体 ReplicationAnalysis 中值判断故障类型。

 不知道为什么从表格中粘贴到博客中每一列的宽度不能调整，这里粘贴为图片，大家凑合看吧

拓扑结构警告类型

• StatementAndMixedLoggingReplicasStructureWarning
• StatementAndRowLoggingReplicasStructureWarning
• MixedAndRowLoggingReplicasStructureWarning
• MultipleMajorVersionsLoggingReplicasStructureWarning
• NoLoggingReplicasStructureWarning
• DifferentGTIDModesStructureWarning
• ErrantGTIDStructureWarning
• NoFailoverSupportStructureWarning
• NoWriteableMasterStructureWarning
• NotEnoughValidSemiSyncReplicasStructureWarning

  核心流程总结

  在实例发现阶段已经将实例的一些基础信息存储到了后台管理数据库的表中，故障发现阶段核心流程：

  1. 执行一个复杂SQL，查询实例和拓扑的状态，在SQL中已经进行了很多逻辑处理，状态对比。
  2. 将该SQL的查询结果存储到结构体ReplicationAnalysis中。
  3. 根据结构体ReplicationAnalysis中的字段进行条件判断，确定故障/失败类型或警告类型。
  4. 在恢复节点就会根据故障类型选择对应的故障处理函数

  与MHA相比

  MHA探活

  核心功能主要有 MHA::HealthCheck::wait_until_unreachable 实现：

  1. 该函数通过一个死循环，检测 4 次，每次 sleep ping_interval 秒（这个值在配置文件指定,参数是 ping_interval），持续四次失败，就认为数据已经宕机；

  2. 如果有二路检测脚本，需要二路检测脚本检测主库宕机，才是真正的宕机，否则只是推出死循环，结束检测，不切换

  3. 通过添加锁来保护数据库的访问，防止脚本多次启动；

  4. 该函数可调用三种检测方法：ping_select、ping_insert、ping_connect

  MHA探活流程图

  

  	MHA	OC
  故障类型	故障类型单一， 主要就是主库是否存活	故障类型丰富 有多种故障与警告类型 见上面的总结
  探活节点	支持多个节点探活 即manager服务器与二次检查脚本中定义的服务器	多个OC节点 以及 配合该实例的从库复制状态是否正常进行检测
  探活方式	ping_select、 ping_insert、 ping_connect	查询被管理的数据库，将数据写入到OC的后台管理数据库中，进行时间戳的比较或状态值比较等方式
  探活间隔	默认3秒	默认每1秒
  探活次数	4次	1次
  故障探测速度	慢，需要多次探活。	快
  探活理念	多次多个节点避免网络抖动等	配合从副本的主从状态以及OC节点的探活

   
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