NDB Cluster Single User Mode NDB Cluster supports a somewhat flexible order for upgrading nodes. When upgrading an NDB Cluster, you may upgrade API nodes (including SQL nodes) before upgrading the management nodes, data nodes, or both. In other words, you are permitted to upgrade the API and SQL nodes in any order. This is subject to the following provisions: This also applies to any MySQL Server version change that may apply, in addition to the NDB engine version change, so do not forget to take this into account when planning the upgrade. (This is true for online upgrades of NDB Cluster in general.) It is not possible for any API node to perform schema operations (such as data definition statements) during a node restart. Due in part to this limitation, schema operations are also not supported during an online upgrade or downgrade. Rolling restarts with multiple management servers.  When performing a rolling restart of an NDB Cluster with multiple management nodes, you should keep in mind that  ndb_mgmd  checks to see if any other management node is running, and, if so, tries to use that node’s configuration data. To keep this from occurring, and to force  ndb_mgmd  to re-read its configuration file, perform the following steps: Regardless of any other options used when starting the first  ndb_mgmd , you should not start any remaining  ndb_mgmd  processes after the first one using  --reload . When performing a rolling restart to update the cluster’s configuration, you can use the config_generation  column of the  ndbinfo.nodes  table to keep track of which data nodes have been successfully restarted with the new configuration. See Section 23.5.14.38, “The ndbinfo nodes Table” . Single user mode  enables the database administrator to restrict access to the database system to a single API node, such as a MySQL server (SQL node) or an instance of  ndb_restore . When entering single user mode, connections to all other API nodes are closed gracefully and all running transactions are aborted. No new transactions are permitted to start. Once the cluster has entered single user mode, only the designated API node is granted access to the database. 23.5.6 NDB Cluster Single User Mode 3. Stop, reconfigure, then restart each cluster SQL node ( mysqld  process) in turn. •This functionality is intended for use as part of an online upgrade only. A mix of node binaries from different NDB Cluster releases is neither intended nor supported for continuous, long-term use in a production setting. •All management nodes must be upgraded before any data nodes are upgraded. This remains true regardless of the order in which you upgrade the cluster’s API and SQL nodes. •Features specific to the “new”  version must not be used until all management nodes and data nodes have been upgraded. 1. Stop all NDB Cluster  ndb_mgmd  processes. 2. Update all  config.ini  files. 3. Start a single  ndb_mgmd  with  --reload ,  --initial , or both options as desired. 4. If you started the first  ndb_mgmd  with the  --initial  option, you must also start any remaining ndb_mgmd  processes using  --initial . 5. Complete the rolling restarts of the data nodes and API nodes as normal. 4478