一、簡介
在實際生產中，數據的重要性不言而喻，因此考慮到數據的重要性比如單點故障導致後端數據庫奔潰，或者後端數據庫訪問壓力過大等，mysql數據庫做主從非常有必要，減輕後端數據庫壓力，主服務器負責讀寫，從服務器只負責讀，這樣一來即保證了數據的可靠性，同時提高服務器的高可用。
MySQL主從複製架構如圖：
MySQL主從複製原理：master服務器將數據的改變記錄二進制日誌，當master上的數據發生改變時，則將其改變寫入二進制日誌中，salve服務器會在一定時間間隔內對master二進制日誌進行探測其是否發生改變，如果發生改變，則開始一個I/OThread請求master二進制事件，同時主節點爲每個I/O線程啓動一個dump線程，用於向其發送二進制事件，並保存至從節點本地的中繼日誌中，從節點將啓動SQL線程從中繼日誌中讀取二進制日誌，在本地重放，使得其數據和主節點的保持一致，最後I/OThread和SQLThread將進入睡眠狀態，等待下一次被喚醒。
二、主從複製配置實現
要求：
1、雙方mysql版本需一致，如不一致，只要主節點低於從節點
2、兩節點間時間需同步
配置：
主服務器配置如下：
1、修改/etc/my.cnf配置文件
log-bin=/mydata/data/binlogs/master-bin
2、創建此目錄並修改屬組屬主爲mysql
mkdir /mydata/binlogs/
chown -R mysql.mysql /mydata/binlogs/
3、授權用戶
grant replication slave,replication client on *.* to 'repluser'@'10.1.10.%' identified by 'pass';
flush privileges;
從服務器配置如下：
1、修改/etc/my.cnf配置文件，註釋二進制日誌，開啓中繼日誌，修改server-id和主節點不一致
server-id=11
relay-log=/mydata/relaylogs/relay-bin
2、創建其目錄並授予此目錄的屬主、屬組爲mysql
mkdir /mydata/relaylogs/
chown -R mysql.mysql /mydata/relaylogs/
3、連接主服務器
change master to master_host='10.1.10.1',master_user='repluser',master_password='pass';
完成上訴配置過程即可各自啓動mysql服務器，且在從服務器上啓動I/O,SQL線程，例如：start slave
測試兩數據可數據是否能同步，則可在主庫上插入數據在從庫上查看是否存在，注意：從庫只能讀，而不能寫
[root@centos6 ~]# mysql Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 13 Server version: 5.5.32-MariaDB MariaDB Server Copyright (c) 2000, 2013, Oracle, Monty Program Ab and others. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. MariaDB [(none)]> show slave status\G; *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 10.1.10.1 Master_User: repluser Master_Port: 3306 Connect_Retry: 60 Master_Log_File: master-bin.000003 Read_Master_Log_Pos: 326 Relay_Log_File: relay-bin.000007 Relay_Log_Pos: 611 Relay_Master_Log_File: master-bin.000003 Slave_IO_Running: Yes #確保I/O和SQL線程開啓，即可實現數據同步 Slave_SQL_Running: Yes #確保I/O和SQL線程開啓，即可實現數據同步 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: 326 Relay_Log_Space: 1184 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 1 row in set (0.00 sec) ERROR: No query specified MariaDB [(none)]> #測試在主庫上刪除dbs,驗證從庫是否存在dbs數據庫，結果如下： MariaDB [(none)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | dbs | | hellodb | | mydbs | | mysql | | performance_schema | | test | +--------------------+ 7 rows in set (0.01 sec) MariaDB [(none)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | hellodb | | mydbs | | mysql | | performance_schema | | test | +--------------------+ 6 rows in set (0.00 sec) MariaDB [(none)]> [root@centos6 ~]# mysql Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 14 Server version: 5.5.32-MariaDB-log MariaDB Server Copyright (c) 2000, 2013, Oracle, Monty Program Ab and others. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. MariaDB [(none)]> MariaDB [(none)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | dbs | | hellodb | | mydbs | | mysql | | performance_schema | | test | +--------------------+ 7 rows in set (0.02 sec) MariaDB [(none)]> drop database dbs; Query OK, 0 rows affected (0.04 sec) MariaDB [(none)]>
三、實戰：主從不同步時，如何進行數據同步至一致
描述：當主服務器已經運行一段時間，並且存在不小的數據時，則需把主服務器備份，然後在從服務器恢復，從備份時所在的位置開始複製。
1、將主服務器上的數據做完全備份
[root@centos6 ~]# mysqldump --lock-all-tables --all-databases --flush-logs --master-data=2 >/root/all.sql
2、在從服務器上導入主服務上的完全備份，在導入時關閉I/O和SQL線程
[root@centos6 ~]# mysql Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 34 Server version: 5.5.32-MariaDB MariaDB Server Copyright (c) 2000, 2013, Oracle, Monty Program Ab and others. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. MariaDB [(none)]> source /root/alren.sql MariaDB [testdbs]> change master to master_host='10.1.10.1',master_user='repluser',master_password='pass',MASTER_LOG_FILE='master-bin.000007',MASTER_LOG_POS=245; Query OK, 0 rows affected (0.02 sec) MariaDB [testdbs]> start slave; Query OK, 0 rows affected (0.02 sec) MariaDB [testdbs]> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 10.1.10.1 Master_User: repluser Master_Port: 3306 Connect_Retry: 60 Master_Log_File: master-bin.000007 #已經恢復到主節點的二進制的位置 Read_Master_Log_Pos: 245 Relay_Log_File: relay-bin.000002 Relay_Log_Pos: 530 Relay_Master_Log_File: master-bin.000007 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: 245 Relay_Log_Space: 818 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 1 row in set (0.00 sec) MariaDB [testdbs]> show tables; +-------------------+ | Tables_in_testdbs | +-------------------+ | tbl | +-------------------+ 1 row in set (0.00 sec) MariaDB [testdbs]> select * from tbl; +-------+ | name | +-------+ | tom | | jerry | | lucy | +-------+ 3 rows in set (0.00 sec) MariaDB [testdbs]> use mydbs; Database changed MariaDB [mydbs]> show tables; #測試數據是否和主節點一致 +-----------------+ | Tables_in_mydbs | +-----------------+ | students | +-----------------+ 1 row in set (0.00 sec) MariaDB [mydbs]> select * from students; +------+-------+ | id | name | +------+-------+ | 1 | tom | | 2 | jerry | +------+-------+ 2 rows in set (0.00 sec) MariaDB [mydbs]>
總結：此實戰中最爲關鍵主要有兩步①主服務器上鎖表做完全備份，並滾動日誌，②從服務器上進行半道恢復.