关于mysql:问题定位-Peronca-Xtrabackup-80近日踩坑总结-xtrabackup-24和80区别

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前言

近期在给 radondb/xenon 适配 percona xtrabackup 8.0 时，遇到了一些问题，通过多日调研、尝试终于解决，特此分享。

版本信息：

Percona-Server 8.0.19-10
Percona-Xtrabackup 8.0.13

版本各字段含意参考 https://www.percona.com/blog/…

适配过程中遇到的坑

一、MySQL 8.0 + Semi-Sync + 继续写入数据期间执行重建后，change master to && start slave 报错：

Last_Error: Could not execute Write_rows event on table db1.t1; Duplicate entry '28646' for key 't1.PRIMARY', Error_code: 1062; handler error HA_ERR_FOUND_DUPP_KEY; the event's master log mysql-bin.000052, end_log_pos 437

二、MySQL 8.0 + Group Replication + 继续写入数据期间执行重建后，change master to && start group_replication 报错：

2020-08-21T14:51:09.977606+08:00 61 [System] [MY-010597] [Repl] 'CHANGE MASTER TO FOR CHANNEL'group_replication_applier'executed'. Previous state master_host='<NULL>', master_port= 0, master_log_file='', master_log_pos= 4, master_bind=''. New state master_host='<NULL>', master_port= 0, master_log_file='', master_log_pos= 4, master_bind=''.
2020-08-21T14:51:09.987494+08:00 61 [ERROR] [MY-013124] [Repl] Slave SQL for channel 'group_replication_applier': Slave failed to initialize relay log info structure from the repository, Error_code: MY-013124
2020-08-21T14:51:09.987542+08:00 61 [ERROR] [MY-011534] [Repl] Plugin group_replication reported: 'Error while starting the group replication applier thread'
2020-08-21T14:51:09.987651+08:00 7 [ERROR] [MY-011669] [Repl] Plugin group_replication reported: 'Unable to initialize the Group Replication applier module.'
2020-08-21T14:51:09.987831+08:00 7 [ERROR] [MY-011735] [Repl] Plugin group_replication reported: '[GCS] The member is leaving a group without being on one.'

要解释这个问题，首先要弄清楚 xtrabackup 2.4 和 8.0 的区别。

xtrabackup 2.4 和 8.0 区别

google 查到 xtrabackup 8.0 与 2.4 版本行为有所不同：

  1. Xtrabackup 2.4 备份后生成的 xtrabackup_binlog_info 文件记录的 GTID 信息是精确的，然而备份复原后 show master status 显示的 GTID 是不精确的。
  2. Xtrabackup 8.0 在备份只有 InnoDB 表的实例时，xtrabackup_binlog_info 文件记录的 GTID 信息不肯定是精确的，然而备份复原后 show master status 显示的 GTID 是精确的。
  3. Xtrabackup 8.0 在备份有非 InnoDB 表格的实例时，xtrabackup_binlog_info 文件记录的 GTID 信息是精确的，备份复原后 show master status 显示的 GTID 也是精确的。

之前钻研过 xtrabackup 2.4，其过程大抵如下：

  1. start backup
  2. copy ibdata1 / copy .ibd file
  3. excuted FTWRL
  4. backup non-InnoDB tables and files
  5. writing xtrabackup_binlog_info
  6. executed FLUSH NO_WRITE_TO_BINLOG ENGINE LOGS
  7. executed UNLOCK TABLES
  8. copying ib_buffer_pool
  9. completed OK!

问题 1：xtrabackup 8.0 的执行过程是什么样？

首先，查看重建期间的general log：

2020-08-26T16:20:18.136376+08:00      170 Query    SET SESSION wait_timeout=2147483
2020-08-26T16:20:18.136439+08:00      170 Query    SET SESSION autocommit=1
2020-08-26T16:20:18.136523+08:00      170 Query    SET NAMES utf8
2020-08-26T16:20:18.136595+08:00      170 Query    SHOW VARIABLES
2020-08-26T16:20:18.138840+08:00      170 Query    SELECT COUNT(*) FROM information_schema.tables WHERE engine = 'MyISAM' OR engine = 'RocksDB'
2020-08-26T16:20:18.140203+08:00      170 Query    SHOW ENGINES
2020-08-26T16:20:18.140407+08:00      170 Query    SHOW ENGINE INNODB STATUS
2020-08-26T16:20:18.141570+08:00      170 Query    SELECT PLUGIN_NAME, PLUGIN_LIBRARY FROM information_schema.plugins WHERE PLUGIN_STATUS = 'ACTIVE' AND PLUGIN_TYPE = 'KEYRING'
2020-08-26T16:20:18.142140+08:00      170 Query    SELECT  CONCAT(table_schema, '/', table_name), engine FROM information_schema.tables WHERE engine NOT IN ('MyISAM', 'InnoDB', 'CSV', 'MRG_MYISAM', 'ROCKSDB') AND table_schema NOT IN ('performance_schema', 'information_schema',   'mysql')
2020-08-26T16:20:18.209819+08:00      171 Query    SET SESSION wait_timeout=2147483
2020-08-26T16:20:18.209879+08:00      171 Query    SET SESSION autocommit=1
2020-08-26T16:20:18.209950+08:00      171 Query    SET NAMES utf8
2020-08-26T16:20:18.210015+08:00      171 Query    SHOW VARIABLES
2020-08-26T16:20:18.214030+08:00      170 Query    SELECT T2.PATH,        T2.NAME,        T1.SPACE_TYPE FROM   INFORMATION_SCHEMA.INNODB_TABLESPACES T1        JOIN INFORMATION_SCHEMA.INNODB_TABLESPACES_BRIEF T2 USING (SPACE) WHERE  T1.SPACE_TYPE = 'Single' && T1.ROW_FORMAT != 'Undo'UNION SELECT T2.PATH,        SUBSTRING_INDEX(SUBSTRING_INDEX(T2.PATH, '/', -1), '.', 1) NAME,        T1.SPACE_TYPE FROM   INFORMATION_SCHEMA .INNODB_TABLESPACES T1        JOIN INFORMATION_SCHEMA .INNODB_TABLESPACES_BRIEF T2 USING (SPACE) WHERE  T1.SPACE_TYPE = 'General' && T1.ROW_FORMAT != 'Undo'
2020-08-26T16:20:19.533904+08:00      170 Query    FLUSH NO_WRITE_TO_BINLOG BINARY LOGS
2020-08-26T16:20:19.543095+08:00      170 Query    SELECT server_uuid, local, replication, storage_engines FROM performance_schema.log_status
2020-08-26T16:20:19.543418+08:00      170 Query    SHOW VARIABLES
2020-08-26T16:20:19.545383+08:00      170 Query    SHOW VARIABLES
2020-08-26T16:20:19.550641+08:00      170 Query    FLUSH NO_WRITE_TO_BINLOG ENGINE LOGS
2020-08-26T16:20:20.556885+08:00      170 Query    SELECT UUID()
2020-08-26T16:20:20.557118+08:00      170 Query    SELECT VERSION()

可见，xtrabackup 8.0 默认状况下大抵过程如下：

  1. start backup
  2. copy .ibd file
  3. backup non-InnoDB tables and files
  4. executed FLUSH NO_WRITE_TO_BINLOG BINARY LOGS
  5. selecting LSN and binary log position from p_s.log_status
  6. copy last binlog file
  7. writing /mysql/backup/backup/binlog.index
  8. writing xtrabackup_binlog_info
  9. executing FLUSH NO_WRITE_TO_BINLOG ENGINE LOGS
  10. copy ib_buffer_pool
  11. completed OK!

留神： 当存在非 InnoDB 表时，xtrabackup 8.0 会执行 FTWRL。

从上述步骤可知，xtrabackup 8.0 与 2.4 的步骤 次要区别 为：

当只存在 InnoDB 引擎的表时，不再执行 FTWRL，而是通过 上述第 5 步（SELECT server_uuid, local, replication, storage_engines FROM performance_schema.log_status）来获取 LSN、binlog position、GTID。

手册中对于表 log_status 的形容如下：

The log_status table provides information that enables an online backup tool to copy the required log files without locking those resources for the duration of the copy process.

When the log_status table is queried, the server blocks logging and related administrative changes for just long enough to populate the table, then releases the resources. The log_status table informs the online backup which point it should copy up to in the source’s binary log and gtid_executed record, and the relay log for each replication channel. It also provides relevant information for individual storage engines, such as the last log sequence number (LSN) and the LSN of the last checkpoint taken for the InnoDB storage engine.

从上述手册形容可知，performance_schema.log_status是 MySQL 8.0 提供给在线备份工具获取复制信息的表格，查问该表时，mysql server 将阻止日志的记录和相干的更改来获取足够的工夫以填充该表，而后开释资源。

log_status 表告诉在线备份工具以后主库的 binlog 的位点和 gtid_executed 的值以及每个复制通道的 relay log。另外，它还提供了各个存储引擎的相干信息，比方，提供了 InnoDB 引擎应用的最初一个日志序列号（LSN）和最初一个检查点的 LSN。

performance_schema.log_status表定义为：

-- Semi-Sync
mysql> select * from performance_schema.log_status\G
*************************** 1. row ***************************
    SERVER_UUID: 6b437e80-e5d5-11ea-88e3-52549922fdbb
          LOCAL: {"gtid_executed": "6b437e80-e5d5-11ea-88e3-52549922fdbb:1-201094", "binary_log_file": "mysql-bin.000079", "binary_log_position": 195}
    REPLICATION: {"channels": []}
STORAGE_ENGINES: {"InnoDB": {"LSN": 23711425885, "LSN_checkpoint": 23711425885}}
1 row in set (0.00 sec)

-- Group Replication
mysql> select * from performance_schema.log_status\G
*************************** 1. row ***************************
    SERVER_UUID: 7bd32480-e5d5-11ea-8f8a-525499cfbb7d
          LOCAL: {"gtid_executed": "aaaaaaaa-aaaa-aaaa-aaaa-53ab6ea1210a:1-11", "binary_log_file": "mysql-bin.000003", "binary_log_position": 1274}
    REPLICATION: {"channels": [{"channel_name": "group_replication_applier", "relay_log_file": "mysql-relay-bin-group_replication_applier.000004", "relay_log_position": 311, "relay_master_log_file": "","exec_master_log_position": 0}, {"channel_name":"group_replication_recovery","relay_log_file":"mysql-relay-bin-group_replication_recovery.000003","relay_log_position": 151,"relay_master_log_file":"", "exec_master_log_position": 0}]}
STORAGE_ENGINES: {"InnoDB": {"LSN": 20257208, "LSN_checkpoint": 20257208}}
1 row in set (0.00 sec)

问题 2：performance_schema.log_status提供的信息是否精确呢？

当写入压力大时，该表中的 binlog position 与 GTID 信息不统一。

mysql> select * from performance_schema.log_status\G  show master status;
*************************** 1. row ***************************
    SERVER_UUID: 6b437e80-e5d5-11ea-88e3-52549922fdbb
          LOCAL: {"gtid_executed": "6b437e80-e5d5-11ea-88e3-52549922fdbb:1-448709", "binary_log_file": "mysql-bin.000087", "binary_log_position": 341265185}
    REPLICATION: {"channels": []}
STORAGE_ENGINES: {"InnoDB": {"LSN": 33797305275, "LSN_checkpoint": 33433316246}}
1 row in set (0.11 sec)

+------------------+-----------+--------------+------------------+-----------------------------------------------+
| File             | Position  | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                             |
+------------------+-----------+--------------+------------------+-----------------------------------------------+
| mysql-bin.000087 | 343317905 |              |                  | 6b437e80-e5d5-11ea-88e3-52549922fdbb:1-448709 |
+------------------+-----------+--------------+------------------+-----------------------------------------------+
1 row in set (0.01 sec)

问题 3：既然 log_status 中的 binlog position 不精确，为什么备份复原后 GTID 并没有缺失，数据也没问题？

起因是 xtrabackup 8.0 在第 4 步 FLUSH NO_WRITE_TO_BINLOG BINARY LOGS 之后，在第 6 步copy last binlog file，这样备份复原出的新实例在启动后不仅会读取 gtid_executed 表，还会读取拷贝的那个 binlog 文件来更新 GTID。

$ mysqlbinlog -vv /data/mysql/mysql-bin.000096 
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=1*/;
/*!50003 SET @OLD_COMPLETION_TYPE=@@COMPLETION_TYPE,COMPLETION_TYPE=0*/;
DELIMITER /*!*/;
# at 4
#200827 11:26:47 server id 575010000  end_log_pos 124 CRC32 0xb026e372     Start: binlog v 4, server v 8.0.19-10 created 200827 11:26:47
# Warning: this binlog is either in use or was not closed properly.
BINLOG '
9ydHXw/Q9EUieAAAAHwAAAABAAQAOC4wLjE5LTEwAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAEwANAAgAAAAABAAEAAAAYAAEGggAAAAICAgCAAAACgoKKioAEjQA
CgFy4yaw
'/*!*/;
# at 124
#200827 11:26:47 server id 575010000  end_log_pos 195 CRC32 0xad060415     Previous-GTIDs
# 6b437e80-e5d5-11ea-88e3-52549922fdbb:1-465503
SET @@SESSION.GTID_NEXT= 'AUTOMATIC' /* added by mysqlbinlog */ /*!*/;
DELIMITER ;
# End of log file
/*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/;
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=0*/;

问题定位

坑一：MySQL 8.0 + Semi-Sync 重建问题

xenon 原有的重建逻辑是适配于 MySQL 5.6、5.7 的（重建过程中 xenon 过程存活），始终无问题：

  1. 禁用 raft，将 xenon 状态设为 LEARNER；
  2. 如 mysql 过程存在，则 stop mysql；
  3. 清空 MySQL 数据目录；
  4. 执行 xtrabackup --backup 以xbstream形式获取对端数据；
  5. 执行 xtrabackup --prepare 利用 redo log；
  6. 启动 mysql；
  7. 执行stop slave; reset slave all；
  8. 执行 reset master，以xtrabackup_binlog_info 文件中的 GTID 为准设置gtid_purged；
  9. 启用 raft，将 xenon 状态设为 FOLLOWER 或 IDLE；
  10. 期待 xenon 主动 change master to 到主节点。
  11. 执行start slave。

问题 1：为什么在 MySQL 8.0 + Semi-Sync 组合下会呈现 Duplicate entry？

跟踪重建过程中的 general log，发现在第 6 和第 7 步两头，也就是设置 gtid_purged 之前凭空多出了 change master to 和 start slave 操作：

2020-08-24T21:55:22.817859+08:00            8 Query     SET GLOBAL rpl_semi_sync_master_enabled=OFF
2020-08-24T21:55:22.818025+08:00            8 Query     SET GLOBAL read_only = 1
2020-08-24T21:55:22.818143+08:00            8 Query     SET GLOBAL super_read_only = 1
2020-08-24T21:55:22.818323+08:00            8 Query     START SLAVE
2020-08-24T21:55:22.824449+08:00            8 Query     STOP SLAVE
2020-08-24T21:55:22.824610+08:00            8 Query     CHANGE MASTER TO MASTER_HOST = '192.168.0.3', MASTER_USER = 'qc_repl', MASTER_PASSWORD = <secret>, MASTER_PORT = 3306, MASTER_AUTO_POSITION = 1
2020-08-24T21:55:22.833710+08:00            8 Query     START SLAVE
2020-08-24T21:55:22.935973+08:00           10 Query     BEGIN
2020-08-24T21:55:22.936084+08:00           10 Query     COMMIT /* implicit, from Xid_log_event */
......
2020-08-24T21:55:24.701711+08:00           10 Query     BEGIN
2020-08-24T21:55:24.701901+08:00           10 Query     COMMIT /* implicit, from Xid_log_event */
2020-08-24T21:55:24.816571+08:00            8 Query     SET GLOBAL rpl_semi_sync_master_enabled=OFF
2020-08-24T21:55:24.816886+08:00            8 Query     SET GLOBAL read_only = 1
2020-08-24T21:55:24.817177+08:00            8 Query     SET GLOBAL super_read_only = 1
2020-08-24T21:55:24.817281+08:00            8 Query     START SLAVE
2020-08-24T21:55:25.039581+08:00           10 Query     BEGIN
2020-08-24T21:55:25.039749+08:00           10 Query     COMMIT /* implicit, from Xid_log_event */
......
2020-08-24T21:55:25.152919+08:00           10 Query     BEGIN
2020-08-24T21:55:25.153082+08:00           10 Query     COMMIT /* implicit, from Xid_log_event */
2020-08-24T21:55:25.389776+08:00            8 Query     STOP SLAVE
2020-08-24T21:55:25.392581+08:00            8 Query     RESET SLAVE ALL
2020-08-24T21:55:25.407434+08:00            8 Query     RESET MASTER
2020-08-24T21:55:25.417292+08:00            8 Query     SET GLOBAL gtid_purged='6b437e80-e5d5-11ea-88e3-52549922fdbb:1-102610'
2020-08-24T21:55:25.419835+08:00            8 Query     START SLAVE
2020-08-24T21:55:25.427071+08:00            8 Query     SET GLOBAL read_only = 1
2020-08-24T21:55:25.427178+08:00            8 Query     SET GLOBAL super_read_only = 1
2020-08-24T21:55:25.427271+08:00            8 Query     SET GLOBAL sync_binlog=1000
2020-08-24T21:55:25.427339+08:00            8 Query     SET GLOBAL innodb_flush_log_at_trx_commit=1
2020-08-24T21:55:25.427423+08:00            8 Query     SHOW SLAVE STATUS
2020-08-24T21:55:25.427600+08:00            8 Query     SHOW MASTER STATUS
2020-08-24T21:55:26.817622+08:00            8 Query     SET GLOBAL rpl_semi_sync_master_enabled=OFF
2020-08-24T21:55:26.817794+08:00            8 Query     SET GLOBAL read_only = 1
2020-08-24T21:55:26.817897+08:00            8 Query     SET GLOBAL super_read_only = 1
2020-08-24T21:55:26.817988+08:00            8 Query     START SLAVE
2020-08-24T21:55:26.818381+08:00            8 Query     SHOW SLAVE STATUS
2020-08-24T21:55:26.818570+08:00            8 Query     SHOW MASTER STATUS
2020-08-24T21:55:26.818715+08:00            8 Query     STOP SLAVE
2020-08-24T21:55:26.818823+08:00            8 Query     CHANGE MASTER TO MASTER_HOST = '192.168.0.3', MASTER_USER = 'qc_repl', MASTER_PASSWORD = <secret>, MASTER_PORT = 3306, MASTER_AUTO_POSITION = 1
2020-08-24T21:55:26.832164+08:00            8 Query     START SLAVE

这就是说在设置 gtid_purged 之前曾经启用复制获取了一部分数据，那么 xtrabackup_binlog_info 中的内容就不再精确，之后设置的 GTID 与理论数据就不统一，理论的数据比设置的 GTID 要多，引起主键抵触。

问题 2：为什么之前 MySQL 5.6、5.7 从没遇到过这个问题呢？

测试了很屡次，发现在 MySQL 5.6 & 5.7 在 set gtid_purged 前执行 change master to & start slave 后会报复制谬误 Slave failed to initialize relay log info structure from the repository，而在reset slave all; reset master、set gtid_purged 后再执行 change master to & start slave 就能够失常复制，数据无误。

问题 3：xenon 中哪块逻辑引起的额定的 change master to 和 start slave？

问题本源在重建期间 xenon 会设为 LEARNER 角色，而该角色在探测到 MySQL Alive 后，会 change master 到主节点。失常来说，要等 raft 状态设为 FOLLOWER 后由 FOLLOWER 的监听线程 change master 到主节点。（代码见 pr104、pr102）

坑二：MySQL 8.0 + Group-Replication 重建后无奈启动 MGR

依据报错信息 Slave failed to initialize relay log info structure from the repository 看，应该是 xtrabackup 重建后的数据目录保留了 slave 复制信息导致的，尝试在启动组复制前执行 reset slave 或 reset slave all 即可解决。

总结

  1. Xtrabackup 2.4 备份后生成的 xtrabackup_binlog_info 文件记录的 GTID 信息是精确的，然而备份复原后 show master status 显示的 GTID 是不精确的。
  2. Xtrabackup 8.0 在备份只有 InnoDB 表的实例时，xtrabackup_binlog_info 文件记录的 GTID 信息不肯定是精确的，然而备份复原后 show master status 显示的 GTID 是精确的。
  3. Xtrabackup 8.0 在备份有非 InnoDB 表格的实例时，xtrabackup_binlog_info 文件记录的 GTID 信息是精确的，备份复原后 show master status 显示的 GTID 也是精确的。
  4. 应用 Xtrabackup 8.0 重建 Semi-Sync 集群节点后，无需执行 reset master & set gtid_purged 操作。
  5. 应用 Xtrabackup 8.0 重建 Group-Replication 集群节点后，启动组复制前须要先执行 reset slave 或 reset slave all 革除 slave 信息，否则 start group_replication 会失败。

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正文完
mysql
发表至： mysql
2020-08-27
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