content_image/666254.jpg
## Configuration change. 

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  To upgrade the cluster to a newer version of the NDB Cluster software (or to downgrade it to an older version).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. 

## System reset (cluster reset). 

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: 

•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. 

Beginning with NDB 8.0.21, this also forces the removal of all Disk Data objects and files associated with those objects. 

•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 . 

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. 

•Use mysqldump  to create a backup prior to the upgrade; afterward, restore the dump using LOAD DATA . 

## Resource Recovery. 

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: 

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. 

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.) 

<img src='content_image/666254.jpg'>

## Note 

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” . 

