The smallest possible cluster for distributed SQL consists of four dedicated or virtual servers. Three servers form the actual database cluster with three nodes that work together as a multi-primary cluster. The database proxy runs on the fourth server. It is the backend for applications and also works as a "cluster manager".
When adding or removing nodes, administrators must keep one thing in mind: the number of cluster nodes must be odd. So, when expanding the basic three-node cluster, two servers must be added. The reason for this requirement: in the event of a failure, the majority of the nodes must be available so that the database proxy can maintain data consistency. With three nodes, only one node can fail without causing problems. The same applies to four nodes: the majority is three nodes, and only one node can fail. These albania telegram screening two cluster configurations therefore have the same fault tolerance. So adding a single node does not increase availability. With five nodes, the situation is different. Here, the majority is also three nodes, but two nodes may fail - the fault tolerance and thus the availability increases.
8. Make sensible use of automatic rebalancing
Part of the typical overhead of distributed SQL is caused by the additional rebalancing required. This means the automatic distribution of sections ( slices ) of the database to different nodes. This technology requires its own computing power and can affect the overall performance of the database at times. Nevertheless, the use of the rebalancer is necessary to maintain the performance of the database. Depending on the application scenario, so-called hotspots can arise in a cluster over a longer period of time: nodes in which frequently used data is concentrated. They are accessed more frequently for reading and writing, with negative consequences for overall performance.