MySQL Replication

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MySQL Replication works only on servers where MySQL 5.x is installed

Mysql logo.png



Create user on Server 1

  • Username: rep2
  • Password: rep2
  • Host: 222.222.222.222
  • Grant all privileges to this user (on database mor)

Create user on Server 2

  • Username: rep1
  • Password: rep1
  • Host: 111.111.111.111
  • Grant all privileges to this user (on database mor)

Server 1 my.cnf

[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock  
# Default to using old password format for compatibility with mysql 3.x
# clients (those using the mysqlclient10 compatibility package).
old_passwords=1

bind-address = 0.0.0.0

binlog-do-db = mor
server-id = 10
auto_increment_increment = 10
auto_increment_offset = 1
master-host = 222.222.222.222
master-user = rep1
master-password = rep1
master-port = 3306
master-connect-retry = 60
replicate-do-db = mor
log-bin = /var/lib/mysql/mysql-bin.log
log-bin-index = /var/lib/mysql/master-log-bin.index
relay-log = /var/lib/mysql/slave-relay.log
relay-log-index = /var/lib/mysql/slave-relay-log.index

max_allowed_packet      = 256M
key_buffer_size=256M
key_buffer=258M

innodb_buffer_pool_size = 100M

query_cache_type=1
query_cache_limit=64M
query_cache_size=64M

join_buffer_size = 2M
tmp_table_size = 512M
max_heap_table_size = 512M
thread_cache_size = 4
table_cache = 128

;log-slow-queries = /var/lib/mysql/slow_query.log

log-error=/var/lib/mysql/mysqld.log

[mysql.server]
user=mysql
basedir=/var/lib

[mysqld_safe]
log-error=/var/lib/mysql/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid


NOTE: if you have file /etc/mysql/debian.cnf make sure you have correct socket location in it: 

socket=/var/lib/mysql/mysql.sock

Or change correct location into mysql.cnf file (e.g. socket=/var/run/mysqld/mysqld.sock)


Server 2 my.cnf

[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock  
# Default to using old password format for compatibility with mysql 3.x
# clients (those using the mysqlclient10 compatibility package).
old_passwords=1

bind-address = 0.0.0.0

binlog-do-db = mor
server-id = 20
auto_increment_increment = 20
auto_increment_offset = 2
master-host = 111.111.111.111
master-user = rep2
master-password = rep2
master-port = 3306
master-connect-retry = 60
replicate-do-db = mor
log-bin = /var/lib/mysql/mysql-bin.log
log-bin-index = /var/lib/mysql/master-log-bin.index
relay-log = /var/lib/mysql/slave-relay.log
relay-log-index = /var/lib/mysql/slave-relay-log.index

max_allowed_packet      = 256M
key_buffer_size=256M
key_buffer=258M

innodb_buffer_pool_size = 100M

query_cache_type=1
query_cache_limit=64M
query_cache_size=64M

join_buffer_size = 2M
tmp_table_size = 512M
max_heap_table_size = 512M
thread_cache_size = 4
table_cache = 128

;log-slow-queries = /var/lib/mysql/slow_query.log

log-error=/var/lib/mysql/mysqld.log

[mysql.server]
user=mysql
basedir=/var/lib

[mysqld_safe]
log-error=/var/lib/mysql/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid


NOTE: if you have file /etc/mysql/debian.cnf make sure you have correct socket location in it: 

socket=/var/lib/mysql/mysql.sock

Or change correct location into mysql.cnf file (e.g. socket=/var/run/mysqld/mysqld.sock


Server 2

Make sure data on Server 2 = data on Server 1. E.g. MySQL table structure and data are identical on both machines.


Server 1

Debian: 

/etc/init.d/mysql restart

Centos/Fedora: 

/etc/init.d/mysqld restart

mysql -u root -p 

USE mor;
FLUSH TABLES WITH READ LOCK; 
SHOW MASTER STATUS;

Remember File and Position. 

UNLOCK TABLES;
quit;



Server2

Check if you can connect to first erver: 

mysql -h 111.111.111.111 -u rep2 -p

Proceed if ok:

Debian: 

/etc/init.d/mysql restart

Centos/Fedora: 

/etc/init.d/mysqld restart

mysql -u root -p 

SLAVE STOP; 

CHANGE MASTER TO MASTER_HOST='111.111.111.111', MASTER_USER='rep2', MASTER_PASSWORD='rep2', MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=98;

NOTE: Change MASTER_HOST, MASTER_LOG_FILE and MASTER_LOG_POS accordingly. 

START SLAVE;

USE mor;
FLUSH TABLES WITH READ LOCK; 
SHOW MASTER STATUS;

Remember File and Position. 

UNLOCK TABLES;
quit;


Server 1

Check if you can connect to first erver: 

mysql -h 222.222.222.222 -u rep1 -p

Proceed if ok: 

mysql -u root -p 

SLAVE STOP; 

CHANGE MASTER TO MASTER_HOST='222.222.222.222', MASTER_USER='rep1', MASTER_PASSWORD='rep1', MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=98;

NOTE: Change MASTER_HOST, MASTER_LOG_FILE and MASTER_LOG_POS accordingly. 

START SLAVE;
quit;



Log files

In order for MySQL Replication to function properly you need to check log files in /var/lib/mysql

Open master-log-bin.index, it should contain names of the files which really exist in same folder. If there's some mismatch - edit this file: enter missing names for files or delete file names which does not represent real files in this folder.

Same with file slave-relay-log.index



Testing

Login to MySQL console on both servers: 

mysql -u root -p

Then: 

SHOW SLAVE STATUS\G

If everything is ok you should see such lines between others on both servers: 

Slave_IO_State: Waiting for master to send event
Slave_IO_Running: Yes
Slave_SQL_Running: Yes


If Replication is off you will see: 

Slave_IO_State:
Slave_IO_Running: No



Troubleshooting

Check file: /var/lib/mysql/mysqld.log

'Could not find first log file name in binary log index file' from master when reading data from binary log

We go to the master and check /var/lib/mysql/master-log-bin.index file.

For example it can show: 

/var/lib/mysql/mysql-bin.000001
/var/lib/mysql/mysql-bin.000002
/var/lib/mysql/mysql-bin.000003
/var/lib/mysql/mysql-bin.000005

In /var/lib/mysql/ we also have file mysql-bin.000004, so its' name is missing in index file, lets add it, so master-log-bin.index looks like: 

/var/lib/mysql/mysql-bin.000001
/var/lib/mysql/mysql-bin.000002
/var/lib/mysql/mysql-bin.000003
/var/lib/mysql/mysql-bin.000004
/var/lib/mysql/mysql-bin.000005

Restart mysql on this server and try with slave again.

This is just an example - some other file's records can be missing. Make sure file has all related file's records which are in same folder.

Failed to open the relay log

  • stop mysql on the slave server
  • find the directory that contains the relay logs (usually /var/lib/mysql)
  • delete all relay logs called hostname-relay-bin.XXX, hostname-relay-bin.index and relay-log.info
  • restart mysql

Your mysql will start with fresh relay logs and is getting the missing data directly from the master server, as there will be probably still bin logs!

Couldn't find MySQL manager or server

Comment out basedir in my.cnf



  • Default mysql.cnf - can be usefull to go back if something goes wrong and no backup is done
  • If server is rebooted - it takes ~45s for database to start synchronizing after MySQL is up
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