背景
“Relay_Log_File” 是 MySQL 中用于复制的参数之一。在 MySQL 复制中，当一个服务器作为主服务器（master）时，它会将其更改写入二进制日志文件（binary log file）。而另一个服务器作为从服务器（slave）时，则会从主服务器复制这些更改，并将它们写入中继日志文件（relay log file）。
需求：
- 搭建的主从复制数据库出现了故障，导致slave异常，同步已经失效。
- 再次重建主从关系时，发现硬盘被大量的Relay_Log_File文件占满，需要清理并释放空间。
- Relay_Log_File文件名称如下图：
数据目录/data硬盘空间已经被占用73%
[ptmauser@mysql-0002 data]$ df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 31G 0 31G 0% /dev
tmpfs 31G 12K 31G 1% /dev/shm
tmpfs 31G 2.3G 29G 8% /run
tmpfs 31G 0 31G 0% /sys/fs/cgroup
/dev/mapper/klas-root 93G 54G 40G 58% /
tmpfs 31G 56K 31G 1% /tmp
/dev/vda1 2.0G 219M 1.8G 11% /boot
/dev/vda2 1022M 20K 1022M 1% /boot/efi
tmpfs 6.2G 0 6.2G 0% /run/user/993
/dev/mapper/datavg-data_lv01 200G 145G 56G 73% /data
tmpfs 6.2G 0 6.2G 0% /run/user/1000
tmpfs 60M 0 60M 0% /var/log/rtlog
tmpfs 6.2G 0 6.2G 0% /run/user/1001
解决：
- 登录mysql-cli，关闭slave实例，通过reset slave实例清除Relay_Log_File文件。
实际操作
登录MySQL-cli
[ptmauser@mysql-0002 data]$ mysql -uroot -p
Enter password:
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MySQL connection id is 27
Server version: 5.7.42-log MySQL Community Server (GPL)Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
检查slave状态
MySQL [(none)]> show slave status\G;
*************************** 1. row ***************************Slave_IO_State: Master_Host: 172.22.88.15Master_User: replMaster_Port: 5575Connect_Retry: 60Master_Log_File: binlog.000097Read_Master_Log_Pos: 911621900Relay_Log_File: mysql-0002-relay-bin.000002Relay_Log_Pos: 148188Relay_Master_Log_File: binlog.000005Slave_IO_Running: NoSlave_SQL_Running: NoReplicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0Last_Error: Skip_Counter: 0Exec_Master_Log_Pos: 148680Relay_Log_Space: 152830684793Until_Condition: NoneUntil_Log_File: Until_Log_Pos: 0Master_SSL_Allowed: NoMaster_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: NoLast_IO_Errno: 0Last_IO_Error: Last_SQL_Errno: 0Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 0Master_UUID: a90b3d6a-419c-11ee-ab08-fa163e5b8157Master_Info_File: /data/data/master.infoSQL_Delay: 0SQL_Remaining_Delay: NULLSlave_SQL_Running_State: Master_Retry_Count: 86400Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: a90b3d6a-419c-11ee-ab08-fa163e5b8157:8-2042286Executed_Gtid_Set: 9553cced-419c-11ee-8f4c-fa163e7c44c3:1-4,
a90b3d6a-419c-11ee-ab08-fa163e5b8157:8-154Auto_Position: 0Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version:
1 row in set (0.000 sec)ERROR: No query specified尝试重启slave实例，并检查状态
MySQL [(none)]> start slave;
Query OK, 0 rows affected (0.002 sec)MySQL [(none)]> show slave status\G;
*************************** 1. row ***************************Slave_IO_State: Queueing master event to the relay logMaster_Host: 172.22.88.15Master_User: replMaster_Port: 5575Connect_Retry: 60Master_Log_File: binlog.000101Read_Master_Log_Pos: 422443924Relay_Log_File: mysql-0002-relay-bin.000002Relay_Log_Pos: 148188Relay_Master_Log_File: binlog.000005Slave_IO_Running: YesSlave_SQL_Running: NoReplicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 1008Last_Error: Error 'Can't drop database 'db_api_data_manager_yw'; database doesn't exist' on query. Default database: 'db_api_data_manager_yw'. Query: 'DROP DATABASE `db_api_data_manager_yw`'Skip_Counter: 0Exec_Master_Log_Pos: 148680Relay_Log_Space: 153306313854Until_Condition: NoneUntil_Log_File: Until_Log_Pos: 0Master_SSL_Allowed: NoMaster_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: NoLast_IO_Errno: 0Last_IO_Error: Last_SQL_Errno: 1008Last_SQL_Error: Error 'Can't drop database 'db_api_data_manager_yw'; database doesn't exist' on query. Default database: 'db_api_data_manager_yw'. Query: 'DROP DATABASE `db_api_data_manager_yw`'Replicate_Ignore_Server_Ids: Master_Server_Id: 8815Master_UUID: a90b3d6a-419c-11ee-ab08-fa163e5b8157Master_Info_File: /data/data/master.infoSQL_Delay: 0SQL_Remaining_Delay: NULLSlave_SQL_Running_State: Master_Retry_Count: 86400Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: 231115 13:59:38Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: a90b3d6a-419c-11ee-ab08-fa163e5b8157:8-2063342Executed_Gtid_Set: 9553cced-419c-11ee-8f4c-fa163e7c44c3:1-4,
a90b3d6a-419c-11ee-ab08-fa163e5b8157:8-154Auto_Position: 0Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version:
1 row in set (0.000 sec)ERROR: No query specified
确认主从关系丢失，已出现了具体的同步报错：
Last_SQL_Error: Error 'Can't drop database 'db_api_data_manager_yw'; database doesn't exist' on query. Default database: 'db_api_data_manager_yw'. Query: 'DROP DATABASE `db_api_data_manager_yw`'
之后再想办法重建主从关系，本文先清理Relay_Log_File文件。
重置slave实例
在MySQL-cli中关闭slave实例，重置slave实例，MySQL将自动清理硬盘上产生的Relay_Log_File文件。
MySQL [(none)]> stop slave;
Query OK, 0 rows affected (0.001 sec)MySQL [(none)]> reset slave;
Query OK, 0 rows affected (2.699 sec)MySQL [(none)]> exit退出MySQL-cli，验证数据目录及relay_log_file文件。
检查硬盘空间及Relay_Log_File
大量堆积的relay-bin-log被成功自动清除。
数据目录/data/硬盘空间已经自动清理，使用率重新回到正常数值2%。
[ptmauser@mysql-0002 data]$ df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 31G 0 31G 0% /dev
tmpfs 31G 12K 31G 1% /dev/shm
tmpfs 31G 2.3G 29G 8% /run
tmpfs 31G 0 31G 0% /sys/fs/cgroup
/dev/mapper/klas-root 93G 54G 40G 58% /
tmpfs 31G 56K 31G 1% /tmp
/dev/vda1 2.0G 219M 1.8G 11% /boot
/dev/vda2 1022M 20K 1022M 1% /boot/efi
tmpfs 6.2G 0 6.2G 0% /run/user/993
/dev/mapper/datavg-data_lv01 200G 2.3G 198G 2% /data
tmpfs 6.2G 0 6.2G 0% /run/user/1000
tmpfs 60M 0 60M 0% /var/log/rtlog
tmpfs 6.2G 0 6.2G 0% /run/user/1001
[ptmauser@mysql-0002 data]$ 注意：
- 避免手动直接删除relay-bin-log文件。
- 重置slave实例前，先关闭slave实例。
