Single-user mode allows the database administrator to restrict
access to the database system to a single MySQL server (SQL
node). When entering single-user mode, all connections to all
other MySQL servers are closed gracefully and all running
transactions are aborted. No new transactions are allowed to be
started.
Once the cluster has entered single-user mode, only the
designated SQL node is granted access to the database.
You can use the ALL STATUS command to see
when the cluster has entered single-user mode.
Example:
NDB> ENTER SINGLE USER MODE 5
After this command has executed and the cluster has entered
single-user mode, the SQL node whose node ID is
5 becomes the cluster's only permitted user.
The node specified in the preceding command must be a MySQL
Server node; An attempt to specify any other type of node will
be rejected.
Note: When the preceding
commmand 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. MySQL Servers waiting for a connection (that is,
for the cluster to become ready and available), are again
permitted to connect. The MySQL Server denoted as the
single-user SQL node continues to run (if still connected)
during and after the state change.
Example:
NDB> EXIT SINGLE USER MODE
There are two recommended ways to handle a node failure when
running in single-user mode:
