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.
You can use the ALL STATUS
command in the
ndb_mgm client to see when the cluster has
entered single user mode. You can also check the
status
column of the
ndbinfo.nodes
table (see
Section 6.15.28, “The ndbinfo nodes Table”, for more
information).
Example:
Press CTRL+C to copyndb_mgm> ENTER SINGLE USER MODE 5
After this command has executed and the cluster has entered single
user mode, the API node whose node ID is 5
becomes the cluster's only permitted user.
The node specified in the preceding command must be an API node; attempting to specify any other type of node is rejected.
When the preceding command is invoked, all transactions running on the designated node are aborted, the connection is closed, and the server must be restarted.
The command EXIT SINGLE USER MODE
changes the
state of the cluster's data nodes from single user mode to
normal mode. API nodes—such as MySQL Servers—waiting
for a connection (that is, waiting for the cluster to become ready
and available), are again permitted to connect. The API node
denoted as the single-user node continues to run (if still
connected) during and after the state change.
Example:
Press CTRL+C to copyndb_mgm> EXIT SINGLE USER MODE
There are two recommended ways to handle a node failure when running in single user mode:
Method 1:
Finish all single user mode transactions
Issue the
EXIT SINGLE USER MODE
commandRestart the cluster's data nodes
Method 2:
Restart storage nodes prior to entering single user mode.