31 October 2014

In past time we use Mysql-MMM (Master-Master Replication Manager). Masters and slaves are separated for write and read. VIP for master active/active, proxy for slave loadbalance.


New emerging solution is MariaDB Galera Cluster. Mirantis is using it in Openstack Fuel.

Mysql servers forms a cluster where all servers are synchronized. Each node can be used to write or read. Transaction returns only after others is synchronized with the writer. It uses wsrep to replicate transaction on row level. A good practice is to use haproxy and desinate only one node as writer, leaving others as reader (all node writeable is prone to deadlock). To avoid brain split, minimum of 3 nodes is recommended. If you have even number of nodes, consider installing Galera Arbitrator (refer to this).

Advantages over MMM:



1. Can’t grep find local ip address

The second MariaDB server failed to start:

mysqld --wsrep_cluster_address=gcomm:// --user=mysql --wsrep_provider=/usr/lib64/galera/libgalera_smm.so --wsrep_sst_auth=root:password

The error output is

141031  7:12:13 [ERROR] WSREP: Failed to read output of: '/sbin/ifconfig | grep -E '^[[:space:]]+inet addr:' | grep -m1 -v 'inet addr:127' | sed 's/:/ /' | awk '{ print $3 }''

Reason is “localization problem”, refer to https://mariadb.atlassian.net/browse/MDEV-4163. I have to provide local ip address in above command:

mysqld --wsrep_cluster_address=gcomm:// --wsrep_sst_receive_address= --user=mysql --wsrep_provider=/usr/lib64/galera/libgalera_smm.so --wsrep_sst_auth=root:password

2. Full restart of the cluster

If one node is down and you want to restart it (cluster is still alive), connect it to any other node. E.g host 1

mysqld --wsrep_cluster_address=gcomm:// --user=mysql --wsrep_provider=/usr/lib64/galera/libgalera_smm.so --wsrep_sst_auth=root:password

Actually you can write config in /etc/my.cnf.


And use service mysql restart.

If the whole cluster is down, given you have the above /etc/my.cnf, restart by

mysqld --wsrep_cluster_address=gcomm:// --user=mysql

This will create a new cluster.

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