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Oskar Calvo
Asked: 2020-11-29 03:42:46 +0800 CST 2020-11-29 03:42:46 +0800 CST

MariaDB & Galera, what happens if a cluster node is lost?

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I am following this tutorial to set up a cluster with MariaDB and Galera.

My question is, if for whatever reason (the machine is turned off, it is removed from the network, etc.) node 1 is affected, will the rest of the nodes continue to maintain database replication?

mariadb

1 Answers

  1. Best Answer

    I comment the following points about the implementation of MariaDB/MySQL/Percona with Galera to clarify doubts:

    • Each node has a complete copy of all data.
    • The availability of at least 3 nodes is recommended in a cluster to avoid split brain . There should always be 50% + 1 quorum. For this there must be an odd number of nodes; 3, 5, 7, 9...
    • There may be the case of having two nodes forming the cluster, a situation that does not meet the minimum defined in the previous point, so you must use Galera Arbitrator to avoid the Split Brain as long as you are writing on both nodes.
    • In case a node stops working, the cluster continues to work, it is transparent. For this to happen, you must add a service such as (HAProxy, ProxySQL / Service Discovery) to automatically discard the affected or donor node and new one.
    • Each node replicates with the number of available nodes. This implies an increase in the bandwidth consumed by the NIC, and an additional cost in CPU Cores to dedicate to this replication process, depending on the high traffic, one of these two resources may be saturated.
    • When a node is added, one of those that already make up the cluster becomes a donor, and will not provide service until all the data has been transferred to the new node and it is synchronized with the cluster, until then neither of them will be available.
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