Performing a Rolling Restart of an NDB Cluster To make a change in the cluster’s configuration, such as adding an SQL node to the cluster, or setting a configuration parameter to a new value. NDB Cluster software upgrade or downgrade.   To upgrade the cluster to a newer version of the NDB Cluster software (or to downgrade it to an older version). This is usually referred to as a “rolling upgrade” (or “rolling downgrade” , when reverting to an older version of NDB Cluster). Change on node host.   To make changes in the hardware or operating system on which one or more NDB Cluster node processes are running. To reset the cluster because it has reached an undesirable state. In such cases it is often desirable to reload the data and metadata of one or more data nodes. This can be done in any of three ways: Beginning with NDB 8.0.21, this also forces the removal of all Disk Data objects and files associated with those objects. See Section 23.5.8, “Online Backup of NDB Cluster” , and Section 23.4.23, “ndb_restore — Restore an NDB Cluster Backup” , for more information. To free memory previously allocated to a table by successive  INSERT  and  DELETE  operations, for re-use by other NDB Cluster tables. The process for performing a rolling restart may be generalized as follows: Some node configuration parameters can be updated by issuing  RESTART  for each of the data nodes in the  ndb_mgm  client following the previous step. Other parameters require that the data node be stopped completely using the management client  STOP  command, then started again from a system shell by invoking the  ndbd  or  ndbmtd  executable as appropriate. (A shell command such as  kill  can also be used on most Unix systems to stop a data node process, but the  STOP  command is preferred and usually simpler.) On Windows, you can also use  SC STOP  and  SC START  commands,  NET STOP  and  NET START  commands, or the Windows Service Manager to stop and start nodes which have been installed as Windows services (see Section 23.2.2.4, “Installing NDB Cluster Processes as Windows Services” ). The type of restart required is indicated in the documentation for each node configuration parameter. See Section 23.3.3, “NDB Cluster Configuration Files” . 4477 Note Configuration change.  System reset (cluster reset).  Resource Recovery.  •Start each data node process ( ndbd  or possibly  ndbmtd ) with the  --initial  option, which forces the data node to clear its file system and to reload all NDB Cluster data and metadata from the other data nodes. •Create a backup using the  ndb_mgm  client  START BACKUP  command prior to performing the restart. Following the upgrade, restore the node or nodes using  ndb_restore . •Use  mysqldump  to create a backup prior to the upgrade; afterward, restore the dump using  LOAD DATA . 1. Stop all cluster management nodes ( ndb_mgmd  processes), reconfigure them, then restart them. (See Rolling restarts with multiple management servers.) 2. Stop, reconfigure, then restart each cluster data node ( ndbd  process) in turn.