故障解析丨Clone节点导致主从故障
1.背景概述
在一次主从复制架构中，由于主节点binlog损坏，导致从节点无法正常同步数据，只能重做从节点；因此使用MySQL 8.0.17开始提供的clone技术进行恢复，恢复后的2天都发生了主从报错数据冲突。
通过解析binlog发现，同一时刻主从节点都在执行同一条语句，因此询问业务是否在主从节点都执行了定时任务，业务回复定时任务只在主节点执行。
最后排查发现，克隆后的从节点的定时任务也会是开启的状态，因此同一时刻，主从节点同时执行定时任务，导致主从报错，最终将从节点的定时任务关闭后解决此问题。
2.问题复现
本次测试基于 GreatSQL 8.0.32-24
greatsql> SELECT VERSION();
+-----------+
| VERSION() |
+-----------+
| 8.0.32-24 |
+-----------+
1 row in set (0.00 sec)
1.搭建一套主从架构
略
2.创建event
greatsql> create database test;
greatsql> use test;
greatsql> CREATE TABLE `test` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT 'ID',
`now` datetime DEFAULT NULL COMMENT '时间',
PRIMARY KEY (`id`)
);
greatsql> CREATE EVENT event_test
ON SCHEDULE EVERY 1 MINUTE
ON COMPLETION PRESERVE
ENABLE
COMMENT '每隔1分钟向test表插入记录'
DO INSERT INTO test VALUES(NULL, now());
3.查看event状态
主节点，默认情况下event状态为 ENABLED
greatsql> show events;
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+
| Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation |
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+
| test | event_test | root@% | SYSTEM | RECURRING | NULL | 1 | MINUTE | 2023-10-12 17:11:14 | NULL | ENABLED | 1 | utf8mb4 | utf8mb4_unicode_ci | utf8mb4_unicode_ci |
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)
从节点，默认情况下event状态为 SLAVESIDE_DISABLED
greatsql> show events;
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+--------------------+------------+----------------------+----------------------+--------------------+
| Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation |
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+--------------------+------------+----------------------+----------------------+--------------------+
| test | event_test | root@% | SYSTEM | RECURRING | NULL | 1 | MINUTE | 2023-10-12 17:11:14 | NULL | SLAVESIDE_DISABLED | 1 | utf8mb4 | utf8mb4_unicode_ci | utf8mb4_unicode_ci |
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+--------------------+------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)
4.查看数据
greatsql> select * from test.test;
+----+---------------------+
| id | now |
+----+---------------------+
| 1 | 2023-08-08 16:00:39 |
| 2 | 2023-08-08 16:01:39 |
| 3 | 2023-08-08 16:02:39 |
+----+---------------------+
3 rows in set (0.00 sec)
5.从节点进行克隆
# 安装克隆插件，主从节点都需要
greatsql> install plugin clone soname 'mysql_clone.so';
# 从节点进行clone
greatsql> set global clone_valid_donor_list='172.17.137.162:6001';
greatsql> clone instance from root@'172.17.137.162':6001 identified by 'greatsql';
6.重新建立主从复制
greatsql> change master to master_user='root',master_password='greatsql',master_host='172.17.137.162',master_port=6001,master_auto_position=1;
Query OK, 0 rows affected, 7 warnings (0.04 sec)
greatsql> start slave;
Query OK, 0 rows affected, 1 warning (0.04 sec)
7.查看主从状态
greatsql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for source to send event
Master_Host: 172.17.137.162
Master_User: root
Master_Port: 6001
Connect_Retry: 60
Master_Log_File: binlog.000001
Read_Master_Log_Pos: 2959
Relay_Log_File: relaylog.000002
Relay_Log_Pos: 395
Relay_Master_Log_File: binlog.000001
Slave_IO_Running: Yes
Slave_SQL_Running: No
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 1062
Last_Error: Coordinator stopped because there were error(s) in the worker(s). The most recent failure being: Worker 1 failed executing transaction 'e8bf88f9-2acd-11ee-a98a-00163e605c74:8' at master log binlog.000001, end_log_pos 2606. See error log and/or performance_schema.replication_applier_status_by_worker table for more details about this failure or others, if any.
Skip_Counter: 0
Exec_Master_Log_Pos: 2307
Relay_Log_Space: 1242
Until_Condition: None
Until_Log_File:
greatsql> select * from performance_schema.replication_applier_status_by_worker limit 1\G
*************************** 1. row ***************************
CHANNEL_NAME:
WORKER_ID: 1
THREAD_ID: NULL
SERVICE_STATE: OFF
LAST_ERROR_NUMBER: 1062
LAST_ERROR_MESSAGE: Worker 1 failed executing transaction 'e8bf88f9-2acd-11ee-a98a-00163e605c74:8' at master log binlog.000001, end_log_pos 2606; Could not execute Write_rows event on table test.test; Duplicate entry '5' for key 'test.PRIMARY', Error_code: 1062; handler error HA_ERR_FOUND_DUPP_KEY; the event's master log FIRST, end_log_pos 2606
LAST_ERROR_TIMESTAMP: 2023-08-08 16:03:39.033240
LAST_APPLIED_TRANSACTION:
LAST_APPLIED_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 0000-00-00 00:00:00.000000
LAST_APPLIED_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 0000-00-00 00:00:00.000000
LAST_APPLIED_TRANSACTION_START_APPLY_TIMESTAMP: 0000-00-00 00:00:00.000000
LAST_APPLIED_TRANSACTION_END_APPLY_TIMESTAMP: 0000-00-00 00:00:00.000000
APPLYING_TRANSACTION: e8bf88f9-2acd-11ee-a98a-00163e605c74:8
APPLYING_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP: 2023-08-08 16:02:45.795753
APPLYING_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP: 2023-08-08 16:02:45.795753
APPLYING_TRANSACTION_START_APPLY_TIMESTAMP: 2023-08-08 16:03:39.032510
LAST_APPLIED_TRANSACTION_RETRIES_COUNT: 0
LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_NUMBER: 0
LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_MESSAGE:
LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_TIMESTAMP: 0000-00-00 00:00:00.000000
APPLYING_TRANSACTION_RETRIES_COUNT: 0
APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_NUMBER: 0
APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_MESSAGE:
APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_TIMESTAMP: 0000-00-00 00:00:00.000000
1 row in set (0.00 sec）
可以看到从节点报错发生了主键冲突。
8.查看从节点定时任务状态
当前从节点定时任务状态为 ENABLED
greatsql> show events;
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+
| Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation |
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+
| test | event_test | root@% | SYSTEM | RECURRING | NULL | 1 | MINUTE | 2023-08-08 15:58:45 | NULL | ENABLED | 1 | utf8mb4 | utf8mb4_unicode_ci | utf8mb4_unicode_ci |
+------+------------+---------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+---------------------+----------------------+--------------------+
1 row in set (0.00 sec)
可以看到由于从节点的定时任务也执行了，从节点写入数据，导致主键冲突。
9.故障解决
greatsql> alter event event_test DISABLE;
Query OK, 0 rows affected (0.01 sec)
关闭从节点的定时任务event，然后跳过主键冲突的报错，最后重新启动主从复制。
3.总结
1.如果主库有定时任务，通过clone的方式搭建从库，在从库恢复之后需要关闭定时任务，避免主从同时执行定时任务导致主从故障。
2.克隆时，如果捐赠节点有主从复制信息，则克隆后的接收节点也会克隆此复制信息，并在克隆完成自动重启实例后，自动启动复制；避免此问题可以在接收节点的配置文件中增加 skip-slave-start，避免节点重启后自动启动复制。
Enjoy GreatSQL 😃
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