之前介绍了主从搭建，具体参考 MySQL：主从复制(Replication)搭建 ，接下来简单介绍 MySQL 主从复制原理。
MySQL 主从复制基于 binary log，这个文件类似于 Oracle 的 redo 和 PostgreSQL WAL 日志文件，用来记录数据库的变化( update, insert, delete 等)，但 SELECT 一般不记录到日志里。
MySQL 主从复制的三个线程
Binlog dump thread
Slave I/O thread
Slave SQL thread
主节点查看: Binlog dump thread
1 2 3 4 5 6 7 8 9 10 11
root@localhost:francs>show processlistG * 2. row * Id: 1493 User: rep1 Host: db2:20976 db: NULL Command: Binlog Dump Time: 1491 State: Master has sent all binlog to slave; waiting for binlog to be updated Info: NULL 2 rows in set (0.00 sec)
备注：主节点状态信息具体查看：Replication Master Thread States
备节点查看: Slave I/O thread 和 Slave SQL thread
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57
root@localhost:francs>show slave statusG * 1. row * Slave_IO_State: Waiting for master to send event Master_Host: 192.168 .2 .37 Master_User: rep1 Master_Port: 3306 Connect_Retry: 60 Master_Log_File: bin-log.000038 Read_Master_Log_Pos: 604 Relay_Log_File: db2-relay-bin.000054 Relay_Log_Pos: 281 Relay_Master_Log_File: bin-log.000038 Slave_IO_Running: Yes Slave_SQL_Running: Yes Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0 Last_Error: Skip_Counter: 0 Exec_Master_Log_Pos: 604 Relay_Log_Space: 855 Until_Condition: None Until_Log_File: Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 0 Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 0 Last_IO_Error: Last_SQL_Errno: 0 Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 1 Master_UUID: 0 c130d47-22bb-11e4-aaaa-000c2986ac80 Master_Info_File: /database/mysql/data/master.info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: Auto_Position: 0 1 row in set (0.00 sec)
备注： 查看 Slave_IO_Running: Yes 和 Slave_SQL_Running: Yes 两项, yes 表示线程正常。Slave_IO_State 表示 I/O THREAD 状态，详细信息参考 Replication Slave I/O Thread States , Slave_SQL_Running_State 表示 SQL thread 状态，详细信息参考 Replication Slave SQL Thread States 。
备节点的 I/O, SQL 两个线程也通过 show processlist 查看
root@localhost:francs>show processlistG
* 2. row *
Id: 7
User: system user
Host:
db: NULL
Command: Connect
Time: 2055
State: Waiting for master to send event
Info: NULL
* 3. row *
Id: 8
User: system user
Host:
db: NULL
Command: Connect
Time: 2038
State: Slave has read all relay log; waiting for the slave I/O thread to update it
Info: NULL
3 rows in set (0.00 sec)
四 参考
原创文章，作者：ItWorker，如若转载，请注明出处：https://blog.ytso.com/239610.html
