Once you add a database and servers to the Enterprise Manager, you are ready to get things rolling. This chapter explains how to start, stop, and pause a database using the Enterprise Manager.
Once you configure the database and add servers, you are ready to start the cluster. Click on the Start Database button next to the database name in the dashboard to start the database.
If your current configuration is not complete (for example, if you specify a K-safety value of 1 but only have one server assigned to the database), the Start Database button is grayed out. Use the dashboard to correct the configuration before starting the database.
When you click on Start Database, the Enterprise Manager presents you with four possible actions:
Create a new database.
Start and recover the database from the command logs of a previous run.
Start and restore a snapshot that was copied to the management server.
Create a replica database.
If you are starting a database for the first time, you must select the first option (creating a new database) because there are no command logs to recover or snapshots to restore. If, during normal operations, you need to restart a database and want to restore a previous known state, you can choose either of the latter two options:
Start and recover — starts the database and replays the command logs from
the last session, reinstating the database contents to their last known state. To recover a database, the previous
database session must have been run with command logging turned on. (If not, the operation fails and you must start
create new database action.) See Section 4.1, “Configuring the Database” for information on
enabling command logging.
Start and restore — starts the database and restores the selected snapshot. Restoring a snapshot restores the contents of the database at a known point in time (when the snapshot was created). You can only restore snapshots that have been copied to the management server. Select the appropriate snapshot to restore from the list in the dialog box. See Section 8.3.1, “Collecting Snapshots” for more information on creating and copying snapshots.
The last option, starting a replica, is part of the database replication process. See the Using VoltDB manual for more information about database replication.
You can also select a startup mode: either normal or administrative mode. To start the database and allow client interactions as soon as the database startup is complete, choose normal mode (the default). If you want to perform administrative functions, or want to restore a snapshot manually (for example, if you are restoring a snapshot created outside of the Enterprise Manager), choose the second option, starting in admin mode.
Admin mode stops the database from accepting transactions on the usual client port; only requests issued over the admin port are accepted. Starting in admin mode prevents clients from accessing the database prematurely and lets you perform administrative tasks over the admin port before initiating client activity.
Once you select an startup option and click Start, the Enterprise Manager performs the following actions:
Generates the appropriate deployment file based on the database configuration.
Copies the necessary files (that is, the VoltDB software, the deployment file, and the runtime catalog) to each of the cluster servers. If you chose to restore a snapshot, the snapshot files are also copied to the cluster.
Starts the VoltDB database on all of the servers and performs the requested actions (such as recover or restore).
While the database is starting, the icon next to its name will "spin". Once the cluster is successfully started, the icon turns green. Or, if you chose to start in admin mode, blue to indicate that the database is paused. If there are any problems, the console will display the associated messages in the log message area in the lower right of the dashboard and the database icon returns to its stopped state.
You can also start a database that is not currently showing in the dashboard. Simply click on the name of the database in the list on the left and select Start from the popup context menu that appears.
Finally, if you choose to start the database in admin mode, be sure to "unpause" the database once you complete your administrative activities. Click on the name of the database in the global list and select Resume from the popup menu to exit admin mode and resume normal operations.