詳解MySQL主從復制實戰(zhàn) - 基于GTID的復制
基于GTID的復制
簡介
基于GTID的復制是MySQL 5.6后新增的復制方式.
GTID (global transaction identifier) 即全局事務ID, 保證了在每個在主庫上提交的事務在集群中有一個唯一的ID.
在原來基于日志的復制中, 從庫需要告知主庫要從哪個偏移量進行增量同步, 如果指定錯誤會造成數(shù)據(jù)的遺漏, 從而造成數(shù)據(jù)的不一致.
而基于GTID的復制中, 從庫會告知主庫已經(jīng)執(zhí)行的事務的GTID的值, 然后主庫會將所有未執(zhí)行的事務的GTID的列表返回給從庫. 并且可以保證同一個事務只在指定的從庫執(zhí)行一次.
實戰(zhàn)
1、在主庫上建立復制賬戶并授予權限
基于GTID的復制會自動地將沒有在從庫執(zhí)行的事務重放, 所以不要在其他從庫上建立相同的賬號. 如果建立了相同的賬戶, 有可能造成復制鏈路的錯誤.
mysql> create user 'repl'@'172.%' identified by '123456';
注意在生產(chǎn)上的密碼必須依照相關規(guī)范以達到一定的密碼強度, 并且規(guī)定在從庫上的特定網(wǎng)段上才能訪問主庫.
mysql> grant replication slave on *.* to 'repl'@'172.%';
查看用戶
mysql> select user, host from mysql.user; +-----------+-----------+ | user | host | +-----------+-----------+ | prontera | % | | root | % | | mysql.sys | localhost | | root | localhost | +-----------+-----------+ 4 rows in set (0.00 sec)
查看授權
mysql> show grants for repl@'172.%'; +--------------------------------------------------+ | Grants for repl@172.% | +--------------------------------------------------+ | GRANT REPLICATION SLAVE ON *.* TO 'repl'@'172.%' | +--------------------------------------------------+ 1 row in set (0.00 sec)
2、配置主庫服務器
[mysqld] log_bin = /var/log/mysql/mysql-bin log_bin_index = /var/log/mysql/mysql-bin.index binlog_format = row server_id = 101 gtid_mode = ON enforce_gtid_consistency = ON #log_slave_updates = ON
NOTE: 把日志與數(shù)據(jù)分開是個好習慣, 最好能放到不同的數(shù)據(jù)分區(qū)
enforce_gtid_consistency 強制GTID一致性, 啟用后以下命令無法再使用
create table ... select ...
mysql> create table dept select * from departments; ERROR 1786 (HY000): Statement violates GTID consistency: CREATE TABLE ... SELECT.
因為實際上是兩個獨立事件, 所以只能將其拆分先建立表, 然后再把數(shù)據(jù)插入到表中
create temporary table
事務內(nèi)部不能創(chuàng)建臨時表
mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> create temporary table dept(id int); ERROR 1787 (HY000): Statement violates GTID consistency: CREATE TEMPORARY TABLE and DROP TEMPORARY TABLE can only be executed outside transactional context. These statements are also not allowed in a function or trigger because functions and triggers are also considered to be multi-statement transactions.
同一事務中更新事務表與非事務表(MyISAM)
mysql> CREATE TABLE `dept_innodb` (id INT(11) UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT); Query OK, 0 rows affected (0.04 sec) mysql> CREATE TABLE `dept_myisam` (id INT(11) UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT) ENGINE = `MyISAM`; Query OK, 0 rows affected (0.03 sec) mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> insert into dept_innodb(id) value(1); Query OK, 1 row affected (0.00 sec) mysql> insert into dept_myisam(id) value(1); ERROR 1785 (HY000): Statement violates GTID consistency: Updates to non-transactional tables can only be done in either autocommitted statements or single-statement transactions, and never in the same statement as updates to transactional tables.
所以建議選擇Innodb作為默認的數(shù)據(jù)庫引擎.
log_slave_updates 該選項在MySQL 5.6版本時基于GTID的復制是必須的, 但是其增大了從服務器的IO負載, 而在MySQL 5.7中該選項已經(jīng)不是必須項
3、配置從庫服務器
master_info_repository 與relay_log_info_repository
在MySQL 5.6.2之前, slave記錄的master信息以及slave應用binlog的信息存放在文件中, 即master.info與relay-log.info. 在5.6.2版本之后, 允許記錄到table中. 對應的表分別為mysql.slave_master_info與mysql.slave_relay_log_info, 且這兩個表均為innodb引擎表.
[mysqld] log_bin = /var/log/mysql/mysql-bin log_bin_index = /var/log/mysql/mysql-bin.index server_id = 102 # slaves relay_log = /var/log/mysql/relay-bin relay_log_index = /var/log/mysql/relay-bin.index relay_log_info_file = /var/log/mysql/relay-bin.info enforce_gtid_consistency = ON log_slave_updates = ON read_only = ON master_info_repository = TABLE relay_log_info_repository = TABLE
4、從庫數(shù)據(jù)初始化 - [optional]
先在主庫上備份數(shù)據(jù)
mysqldump --single-transaction --master-data=2 --triggers --routines --all-databases --events -u root -p > backup.sql
—master-data=2 該選項將當前服務器的binlog的位置和文件名追加到輸出文件中(show master status). 如果為1, 將偏移量拼接到CHANGE MASTER 命令. 如果為2, 輸出的偏移量信息將會被注釋。
--all-databases 因為基于GTID的復制會記錄全部的事務, 所以要構建一個完整的dump這個選項是推薦的
常見錯誤
當從庫導入SQL的時候出現(xiàn)
ERROR 1840 (HY000) at line 24: @@GLOBAL.GTID_PURGED can only be set when @@GLOBAL.GTID_EXECUTED is empty.
此時進入從庫的MySQL Command Line, 使用reset master即可
5、啟動基于GTID的復制
現(xiàn)有master@172.20.0.2和slave@172.20.0.3, 并且已經(jīng)通過mysqldump將數(shù)據(jù)同步至從庫slave中. 現(xiàn)在在從服務器slave上配置復制鏈路
mysql> change master to master_host='master', master_user='repl', master_password='123456', master_auto_position=1; Query OK, 0 rows affected, 2 warnings (0.06 sec)
啟動復制
mysql> start slave;
啟動成功后查看slave的狀態(tài)
mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Queueing master event to the relay log
Master_Host: master
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000002
Read_Master_Log_Pos: 12793692
Relay_Log_File: relay-bin.000002
Relay_Log_Pos: 1027
Relay_Master_Log_File: mysql-bin.000002
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: 814
Relay_Log_Space: 12794106
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: 5096
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: 101
Master_UUID: a9fd4765-ec70-11e6-b543-0242ac140002
Master_Info_File: mysql.slave_master_info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Reading event from the relay log
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set: a9fd4765-ec70-11e6-b543-0242ac140002:1-39
Executed_Gtid_Set: a9fd4765-ec70-11e6-b543-0242ac140002:1-4
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
當Slave_IO_Running, Slave_SQL_Running為YES,
且Slave_SQL_Running_State 為Slave has read all relay log; waiting for more updates時表示成功構建復制鏈路
6、總結
優(yōu)點
- 因為不用手工設置日志偏移量, 可以很方便地進行故障轉移
- 如果啟用log_slave_updates那么從庫不會丟失主庫上的任何修改
缺點
- 對執(zhí)行的SQL有一定限制
- 僅支持MySQL 5.6之后的版本, 而且不建議使用早期5.6版本
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