This guide describes the procedure for setting up Percona XtraDB Cluster 5.7 on Ubuntu 18.04 LTS three nodes in a multi-master replication . Multi-master replication allows writing of records in each node, so if a node will fail, we can work on the other as if nothing happened. First of all, why we choose three nodes and not only two? In any cluster, the number of nodes should be odd, so in the case of disconnection of a node, we assume that the highest group of servers has the fresh data, and should be replicated to the down node to avoid data loss. This is related only to resolve conflicts in data replication, we won't loose data written only to the disconnected node. This is used to avoid a circumstance called split brain, in which we can't automatically choose which node has correct data. Think for example of a 2 node cluster where both nodes are disconnected from each other, and the same record is written to both nodes: who wins when they come back online? We don't kn...
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