NDB Cluster Configuration Files watching it uses 1000 milliseconds, obviously the node is declared dead very quickly. This parameter can be changed during an online software upgrade, but only in small increments. See also Network communication and latency, as well as the description of the ConnectCheckIntervalDelay  configuration parameter. Each data node sends heartbeat signals to each MySQL server (SQL node) to ensure that it remains in contact. If a MySQL server fails to send a heartbeat in time it is declared “dead,”  in which case all ongoing transactions are completed and all resources released. The SQL node cannot reconnect until all activities initiated by the previous MySQL instance have been completed. The three-heartbeat criteria for this determination are the same as described for  HeartbeatIntervalDbDb . The default interval is 1500 milliseconds (1.5 seconds). This interval can vary between individual data nodes because each data node watches the MySQL servers connected to it, independently of all other data nodes. For more information, see Network communication and latency. Data nodes send heartbeats to one another in a circular fashion whereby each data node monitors the previous one. If a heartbeat is not detected by a given data node, this node declares the previous data node in the circle “dead”  (that is, no longer accessible by the cluster). The determination that a data node is dead is done globally; in other words; once a data node is declared dead, it is regarded as such by all nodes in the cluster. It is possible for heartbeats between data nodes residing on different hosts to be too slow compared to heartbeats between other pairs of nodes (for example, due to a very low heartbeat interval or temporary connection problem), such that a data node is declared dead, even though the node can still function as part of the cluster. . In this type of situation, it may be that the order in which heartbeats are transmitted between data nodes makes a difference as to whether or not a particular data node is declared dead. If this declaration 4105 • HeartbeatOrder • HeartbeatIntervalDbApi Version (or later) NDB 8.0.13 Type or units milliseconds Default 1500 Range 100 - 4294967039 (0xFFFFFEFF) Restart Type N (NDB 8.0.13) Version (or later) NDB 8.0.13 Type or units numeric Default 0 Range 0 - 65535 Restart Type S (NDB 8.0.13)