One 、 To configure mariadb Master-slave replication of

mariadb Master-slave replication of

Two 、 The principle of semi synchronous replication

 Solve the inconsistency between master and slave database data , Main database data hang up , Inconsistent data from the database 
 resolvent ： Semi-synchronous replication 
 In a semi synchronous replication scenario ,master Will monitor all slave, Ensure that at least one of the data is fully synchronized successfully ,master Will return the client information , This data was written successfully .

3、 ... and 、 Main storage failure , Promote the method of slave library and master library

1.keepalived Switch

VIP,
 adopt keepalived Judging scripts , Execution switching VIP

2. Through semi synchronous replication

  Three nodes are required , One master and two slaves , Automatic switch , One of them slave Turn on semi synchronous replication 

Four 、 The difference between asynchronous replication and semi synchronous replication

1. Asynchronous replication

 Asynchronous replication ：
 Simply speaking , Namely master hold binlog Send past , No matter slave Whether to accept , No matter the execution is finished , This action is over .

2. Semi-synchronous replication

 Semi-synchronous replication ：
master hold binlog Send past ,slave Confirm that... Has been received , But whether it's done or not , Will give master Send a message, I received , This action is over .

3. Disadvantages of asynchrony

 Disadvantages of asynchrony ：
 When master When the write operation is busy ,  When the write up operation is busy , At present Pos Point e.g 10, and 
slave, On I0_ THREAD The thread receives 3, here master Downtime , Will cause a difference 7 individual 
 Point not transferred to slave And data loss .

5、 ... and 、mariadb Semi synchronous configuration

1.master To configure

① Turn on the master database semi synchronization

MariaDB [(none)]>  set global rpl_semi_sync_master_enabled = 1;
Query OK, 0 rows affected (0.058 sec)

② Length of time to wait for response from the library

MariaDB [(none)]> set global rpl_semi_sync_master_timeout = 3000;
Query OK, 0 rows affected (0.000 sec)

2.slave To configure

① Enable semi synchronous replication from the library

MariaDB [(none)]> set global rpl_semi_sync_slave_enabled = 1;
Query OK, 0 rows affected (0.296 sec)

② Restart from the library

MariaDB [(none)]> stop slave;
Query OK, 0 rows affected (0.484 sec)

MariaDB [(none)]> start slave;
Query OK, 0 rows affected (0.258 sec)

MariaDB [(none)]>