mysql主从复制是最常见的高可用方式，通过主-从的方式，实现系统的高可用。在生产环境种，通常采用一主多从的方式，通过主库写数据，从库读数据，来提升系统的性能。
现在就演示一下，mysql5.7之下，如何配置主从复制。
1. 环境准备
两台安装好mysql数据库的服务器如下：
| 序号 | 服务器IP | 主/从 | mysql版本 |
|---|---|---|---|
| 1 | 192.168.161.114 | 主 | 5.7.34 |
| 2 | 192.168.161.115 | 从 | 5.7.34 |
2.主库配置
查看主库log配置：
mysql> show global variables like '%log%';
+--------------------------------------------+------------------------------------------+
| Variable_name | Value |
+--------------------------------------------+------------------------------------------+
| back_log | 300 |
| binlog_cache_size | 1048576 |
| binlog_checksum | CRC32 |
| binlog_direct_non_transactional_updates | OFF |
| binlog_error_action | ABORT_SERVER |
| binlog_format | MIXED |
| binlog_group_commit_sync_delay | 0 |
| binlog_group_commit_sync_no_delay_count | 0 |
| binlog_gtid_simple_recovery | ON |
| binlog_max_flush_queue_time | 0 |
| binlog_order_commits | ON |
| binlog_row_image | FULL |
| binlog_rows_query_log_events | OFF |
| binlog_stmt_cache_size | 32768 |
| binlog_transaction_dependency_history_size | 25000 |
| binlog_transaction_dependency_tracking | COMMIT_ORDER |
| expire_logs_days | 30 |
| general_log | OFF |
| general_log_file | /opt/mysql/data/m161p114.log |
| innodb_api_enable_binlog | OFF |
| innodb_flush_log_at_timeout | 1 |
| innodb_flush_log_at_trx_commit | 2 |
| innodb_locks_unsafe_for_binlog | OFF |
| innodb_log_buffer_size | 2097152 |
| innodb_log_checksums | ON |
| innodb_log_compressed_pages | ON |
| innodb_log_file_size | 33554432 |
| innodb_log_files_in_group | 3 |
| innodb_log_group_home_dir | ./ |
| innodb_log_write_ahead_size | 8192 |
| innodb_max_undo_log_size | 1073741824 |
| innodb_online_alter_log_max_size | 134217728 |
| innodb_undo_log_truncate | OFF |
| innodb_undo_logs | 128 |
| log_bin | ON |
| log_bin_basename | /opt/mysql/data/mysql-bin |
| log_bin_index | /opt/mysql/data/mysql-bin.index |
| log_bin_trust_function_creators | OFF |
| log_bin_use_v1_row_events | OFF |
| log_builtin_as_identified_by_password | OFF |
| log_error | /opt/mysql/log/mysql-error.log |
| log_error_verbosity | 3 |
| log_output | FILE |
| log_queries_not_using_indexes | OFF |
| log_slave_updates | OFF |
| log_slow_admin_statements | OFF |
| log_slow_slave_statements | OFF |
| log_statements_unsafe_for_binlog | ON |
| log_syslog | OFF |
| log_syslog_facility | daemon |
| log_syslog_include_pid | ON |
| log_syslog_tag | |
| log_throttle_queries_not_using_indexes | 0 |
| log_timestamps | UTC |
| log_warnings | 2 |
| max_binlog_cache_size | 18446744073709547520 |
| max_binlog_size | 1073741824 |
| max_binlog_stmt_cache_size | 18446744073709547520 |
| max_relay_log_size | 0 |
| relay_log | |
| relay_log_basename | /opt/mysql/data/m161p114-relay-bin |
| relay_log_index | /opt/mysql/data/m161p114-relay-bin.index |
| relay_log_info_file | relay-log.info |
| relay_log_info_repository | FILE |
| relay_log_purge | ON |
| relay_log_recovery | OFF |
| relay_log_space_limit | 0 |
| slow_query_log | ON |
| slow_query_log_file | /opt/mysql/log/mysql-slow.log |
| sql_log_off | OFF |
| sync_binlog | 1 |
| sync_relay_log | 10000 |
| sync_relay_log_info | 10000 |
+--------------------------------------------+------------------------------------------+
73 rows in set (0.01 sec)
查看主库日志文件：
mysql> show master logs;
+------------------+-----------+
| Log_name | File_size |
+------------------+-----------+
| mysql-bin.000001 | 177 |
| mysql-bin.000002 | 711 |
| mysql-bin.000003 | 1225 |
| mysql-bin.000004 | 177 |
| mysql-bin.000005 | 154 |
+------------------+-----------+
5 rows in set (0.00 sec)
查看主库server相关配置：
mysql> show global variables like '%server%';
+---------------------------------+--------------------------------------+
| Variable_name | Value |
+---------------------------------+--------------------------------------+
| character_set_server | utf8 |
| collation_server | utf8_general_ci |
| innodb_ft_server_stopword_table | |
| server_id | 1 |
| server_id_bits | 32 |
| server_uuid | 10dfcf35-16c2-11ec-9238-5254003c7ee2 |
+---------------------------------+--------------------------------------+
6 rows in set (0.00 sec)
主库创建一个用于复制的用户：
mysql> create user 'repl'@'%' identified by '123456';
Query OK, 0 rows affected (0.00 sec)
将replication slave,replication client 授权到repl用户：
mysql> grant replication slave,replication client on *.* to 'repl'@'%';
Query OK, 0 rows affected (0.00 sec)
刷新权限：
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
查看主库status:
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000005 | 767 | | | |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)
可以看到，此时主库当前日志的最后一个文件为005，且position为767.
2.从库配置
查看从库的log配置：
mysql> show global variables like '%log%';
+--------------------------------------------+---------------------------------------+
| Variable_name | Value |
+--------------------------------------------+---------------------------------------+
| back_log | 300 |
| binlog_cache_size | 1048576 |
| binlog_checksum | CRC32 |
| binlog_direct_non_transactional_updates | OFF |
| binlog_error_action | ABORT_SERVER |
| binlog_format | MIXED |
| binlog_group_commit_sync_delay | 0 |
| binlog_group_commit_sync_no_delay_count | 0 |
| binlog_gtid_simple_recovery | ON |
| binlog_max_flush_queue_time | 0 |
| binlog_order_commits | ON |
| binlog_row_image | FULL |
| binlog_rows_query_log_events | OFF |
| binlog_stmt_cache_size | 32768 |
| binlog_transaction_dependency_history_size | 25000 |
| binlog_transaction_dependency_tracking | COMMIT_ORDER |
| expire_logs_days | 30 |
| general_log | OFF |
| general_log_file | /opt/mysql/data/m161p115.log |
| innodb_api_enable_binlog | OFF |
| innodb_flush_log_at_timeout | 1 |
| innodb_flush_log_at_trx_commit | 2 |
| innodb_locks_unsafe_for_binlog | OFF |
| innodb_log_buffer_size | 2097152 |
| innodb_log_checksums | ON |
| innodb_log_compressed_pages | ON |
| innodb_log_file_size | 33554432 |
| innodb_log_files_in_group | 3 |
| innodb_log_group_home_dir | ./ |
| innodb_log_write_ahead_size | 8192 |
| innodb_max_undo_log_size | 1073741824 |
| innodb_online_alter_log_max_size | 134217728 |
| innodb_undo_log_truncate | OFF |
| innodb_undo_logs | 128 |
| log_bin | ON |
| log_bin_basename | /opt/mysql/data/mysql-bin |
| log_bin_index | /opt/mysql/data/mysql-bin.index |
| log_bin_trust_function_creators | OFF |
| log_bin_use_v1_row_events | OFF |
| log_builtin_as_identified_by_password | OFF |
| log_error | /opt/mysql/log/mysql-error.log |
| log_error_verbosity | 3 |
| log_output | FILE |
| log_queries_not_using_indexes | OFF |
| log_slave_updates | OFF |
| log_slow_admin_statements | OFF |
| log_slow_slave_statements | OFF |
| log_statements_unsafe_for_binlog | ON |
| log_syslog | OFF |
| log_syslog_facility | daemon |
| log_syslog_include_pid | ON |
| log_syslog_tag | |
| log_throttle_queries_not_using_indexes | 0 |
| log_timestamps | UTC |
| log_warnings | 2 |
| max_binlog_cache_size | 18446744073709547520 |
| max_binlog_size | 1073741824 |
| max_binlog_stmt_cache_size | 18446744073709547520 |
| max_relay_log_size | 0 |
| relay_log | slave-relay-bin |
| relay_log_basename | /opt/mysql/data/slave-relay-bin |
| relay_log_index | /opt/mysql/data/slave-relay-bin.index |
| relay_log_info_file | relay-log.info |
| relay_log_info_repository | FILE |
| relay_log_purge | ON |
| relay_log_recovery | OFF |
| relay_log_space_limit | 0 |
| slow_query_log | ON |
| slow_query_log_file | /opt/mysql/log/mysql-slow.log |
| sql_log_off | OFF |
| sync_binlog | 1 |
| sync_relay_log | 10000 |
| sync_relay_log_info | 10000 |
+--------------------------------------------+---------------------------------------+
73 rows in set (0.01 sec)
查看从库的server配置：
mysql> show global variables like '%server%';
+---------------------------------+--------------------------------------+
| Variable_name | Value |
+---------------------------------+--------------------------------------+
| character_set_server | utf8 |
| collation_server | utf8_general_ci |
| innodb_ft_server_stopword_table | |
| server_id | 2 |
| server_id_bits | 32 |
| server_uuid | 03cb46fa-16bc-11ec-9550-525400ea020a |
+---------------------------------+--------------------------------------+
6 rows in set (0.00 sec)
查看从库的master日志：
mysql> show master logs;
+------------------+-----------+
| Log_name | File_size |
+------------------+-----------+
| mysql-bin.000001 | 177 |
| mysql-bin.000002 | 711 |
| mysql-bin.000003 | 1225 |
| mysql-bin.000004 | 177 |
| mysql-bin.000005 | 177 |
| mysql-bin.000006 | 154 |
+------------------+-----------+
6 rows in set (0.00 sec)
查看从库的status:
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000006 | 154 | | | |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)
现在对从库进行配置：
mysql> change master to master_host='192.168.161.114',master_user='repl',master_password='123456',master_log_file='mysql-bin.000005',master_log_pos=767;
Query OK, 0 rows affected, 2 warnings (0.02 sec)
需要注意的是，master_log_file 与master_log_pos 均要指向主库对应的日志文件的最后一个文件。
此处的指向为前面第一部分中查看的日志的值master_log_file='mysql-bin.000005',master_log_pos=767。
3.启动从库
查看从库的status:
mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State:
Master_Host: 192.168.161.114
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000005
Read_Master_Log_Pos: 767
Relay_Log_File: slave-relay-bin.000001
Relay_Log_Pos: 4
Relay_Master_Log_File: mysql-bin.000005
Slave_IO_Running: No
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: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 767
Relay_Log_Space: 154
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: NULL
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: 0
Master_UUID:
Master_Info_File: /opt/mysql/data/master.info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State:
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
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.01 sec)
ERROR:
No query specified
因为没有启动从节点的复制线程，这两个参数都为NO.
Slave_IO_Running: No
Slave_SQL_Running: No
现在启动主从复制：
mysql> start slave;
Query OK, 0 rows affected (0.00 sec)
再次查看从库节点的状态：
mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.161.114
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000005
Read_Master_Log_Pos: 767
Relay_Log_File: slave-relay-bin.000002
Relay_Log_Pos: 320
Relay_Master_Log_File: mysql-bin.000005
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: 767
Relay_Log_Space: 527
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: 10dfcf35-16c2-11ec-9238-5254003c7ee2
Master_Info_File: /opt/mysql/data/master.info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
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
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
ERROR:
No query specified
可以看到这两个参数都为yes.
Slave_IO_Running: Yes
Slave_SQL_Running: Yes。
需要注意的是，并不是所有的库操作都要同步到从库，因此，可以在主库的配置上增加如下配置:
# 不同步哪些数据库
binlog-ignore-db = mysql
binlog-ignore-db = test
binlog-ignore-db = information_schema
# 只同步哪些数据库，除此之外，其他不同步
binlog-do-db = gts
这样可以将需要同步的数据库进行指定。
4.主从不一致问题
不小心在从库上执行了写操作，这样导致从库的Slave_SQL_Running停止：
mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.161.114
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000006
Read_Master_Log_Pos: 509
Relay_Log_File: slave-relay-bin.000005
Relay_Log_Pos: 367
Relay_Master_Log_File: mysql-bin.000006
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: 1008
Last_Error: Error 'Can't drop database 'gts'; database doesn't exist' on query. Default database: 'gts'. Query: 'drop database gts'
Skip_Counter: 0
Exec_Master_Log_Pos: 154
Relay_Log_Space: 1095
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: NULL
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 1008
Last_SQL_Error: Error 'Can't drop database 'gts'; database doesn't exist' on query. Default database: 'gts'. Query: 'drop database gts'
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1
Master_UUID: 10dfcf35-16c2-11ec-9238-5254003c7ee2
Master_Info_File: /opt/mysql/data/master.info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State:
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp: 210917 20:18:56
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position: 0
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
解决办法,如果主从不同步，可以通过如下方法强行跳过：
mysql> stop slave;
Query OK, 0 rows affected (0.00 sec)
mysql> set global sql_slave_skip_counter=1;
Query OK, 0 rows affected (0.00 sec)
mysql> start slave;
Query OK, 0 rows affected (0.00 sec)
强行跳过之后，主从就能一致了。
现在在主库上创建一个gts数据库，从库上就能同步到了。
主库执行如下语句：
create database gts DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
从库下就能查询到了：
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| gts |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.01 sec)
这说明，从库上要设置为只读：
设置：read_only = ON,但是此限制对拥有SUPER权限 的用户均无效。
阻止所有用户的方法,在从库上执行如下语句：
mysql> flush tables with read lock;
Query OK, 0 rows affected (0.00 sec)
至此，mysql的主从复制配置完成。
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