Data is distributed across all the data nodes, and the backup occurs in parallel across all nodes, so that all data in the cluster is captured. The scanning and logging are synchronised so that the backup is a snapshot at a single point in time. At the same time, a log of ongoing changes is also recorded. When a backup starts, each data node scans the set of table partitions it owns, writing their records to its local disk. At any time, each partition is logically owned by just one node in one nodegroup, which is responsible for including it in a backup. Different nodegroups contain different sets of partitions. All data nodes in a nodegroup (up to four) contain the same sets of partitions, kept in sync at all times. The data nodes are logically grouped into nodegroups. In NDB Cluster, tables are horizontally partitioned into a set of partitions, which are then distributed across the data nodes in the cluster. NDB Cluster Backup & Restore concept in brief:
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