Class SlaveController

  • All Implemented Interfaces:
    ModuleControl, ModuleSupportable, SlaveFactory

    public class SlaveController
    extends java.lang.Object
    implements SlaveFactory, ModuleControl, ModuleSupportable

    This is an implementation of the replication slave controller service. The service is booted when this instance of Derby will have the replication slave role for this database.

    Note: The current version of the class is far from complete. Code to control the replication slave behavior will be added as more parts of the replication functionality is added to Derby.

    See Also:
    SlaveFactory
    • Field Detail

      • DEFAULT_SOCKET_TIMEOUT

        private static final int DEFAULT_SOCKET_TIMEOUT
        See Also:
        Constant Field Values
      • dbname

        private java.lang.String dbname
      • highestLogInstant

        private volatile long highestLogInstant
        The instant of the latest log record received from the master and processed so far. Used to check that master and slave log files are in synch
      • inReplicationSlaveMode

        private volatile boolean inReplicationSlaveMode
        Whether or not replication slave mode is still on. Will be set to false when slave replication is shut down. The value of this variable is checked after every timeout when trying to set up a connection to the master, and by the thread that applies log chunks received from the master.
      • startupSuccessful

        private volatile boolean startupSuccessful
        Whether or not this SlaveController has been successfully started, including setting up a connection with the master and starting the log receiver thread. The client connection that initiated slave replication mode on this database will not report that slave mode was successfully started (i.e., it will hang) until startupSuccessful has been set to true
    • Constructor Detail

      • SlaveController

        public SlaveController()
        Empty constructor required by Monitor.bootServiceModule
    • Method Detail

      • boot

        public void boot​(boolean create,
                         java.util.Properties properties)
                  throws StandardException
        Used by Monitor.bootServiceModule to start the service. It will set up basic variables
        Specified by:
        boot in interface ModuleControl
        Parameters:
        create - Currently ignored
        properties - Properties used to start the service in the correct mode
        Throws:
        StandardException - Standard Derby exception policy, thrown on error.
        See Also:
        Monitor, ModuleFactory
      • canSupport

        public boolean canSupport​(java.util.Properties startParams)
        Used by Monitor.bootServiceModule to check if this class is usable for replication. To be usable, we require that slave replication mode is specified in startParams by checking that a property with key SlaveFactory.REPLICATION_MODE has the value SlaveFactory.SLAVE_MODE.
        Specified by:
        canSupport in interface ModuleSupportable
        Parameters:
        startParams - The properties used to start replication
        Returns:
        true if slave repliation is specified, meaning that this MasterController is a suitable implementation for the SlaveFactory service. False otherwise.
        See Also:
        ModuleSupportable.canSupport(java.util.Properties)
      • startSlave

        public void startSlave​(RawStoreFactory rawStore,
                               LogFactory logFac)
                        throws StandardException
        Start slave replication. This method establishes a network connection with the associated replication master and starts a thread that applies operations received from the master (in the form of log records) to the local slave database.
        Specified by:
        startSlave in interface SlaveFactory
        Parameters:
        rawStore - The RawStoreFactory for the database
        logFac - The LogFactory ensuring recoverability for this database
        Throws:
        StandardException - Thrown if the slave could not be started.
      • stopSlave

        public void stopSlave​(boolean forcedStop)
                       throws StandardException
        Description copied from interface: SlaveFactory
        Stop replication slave mode. Causes the database to abort the boot process, and should only be used when shutting down this database. If forcedStop is false, the method will fail with an exception if connected with the master. If forcedStop is true, the slave will be shut down even if connected to the master. A forcedStop value of true should only be used by system shutdown.
        Specified by:
        stopSlave in interface SlaveFactory
        Parameters:
        forcedStop - Determines whether or not an exception should be thrown when this method is called while the network connection to the master is up.
        Throws:
        StandardException - Thrown if slave is connected with master and forcedStop is false.
        See Also:
        SlaveFactory.stopSlave(boolean)
      • failover

        public void failover()
                      throws StandardException
        Description copied from interface: SlaveFactory

        Used to turn this slave instance of the database into a normal instance that clients can connect to, assuming that the connection with the master is down. This is typically done in cases where a fatal error has happened on the master instance of the database, or when the master database is unreachable due to network problems.

        By calling failover, this slave instance of the database will be recovered so that all committed operations that have been received from the master are reflected here. On the other hand, operations from transactions where the commit log record has not been received from the master will not be reflected.

        Note that even though an operation has been executed (and even committed) on the master, it is not neccessarily reflected in the slave instance of the database. This depends on the replication strategy used by the MasterFactory.

        Specified by:
        failover in interface SlaveFactory
        Throws:
        StandardException - Thrown if slave is connected with master
        See Also:
        MasterFactory, MasterController.flushedTo(long)
      • doFailover

        private void doFailover()
        Performs failover on this database. May be called because a failover command has been received from the master, or because a client has requested a failover after the network connection with the master has been lost.
        See Also:
        SlaveFactory.failover()
      • isStarted

        public boolean isStarted()
        Description copied from interface: SlaveFactory
        Check whether or not slave replication mode has been successfully started.
        Specified by:
        isStarted in interface SlaveFactory
        Returns:
        true if slave replication mode has started successfully, false if slave mode startup is not yet confirmed
        See Also:
        SlaveFactory.isStarted()
      • setupConnection

        private boolean setupConnection()
                                 throws StandardException
        Establish a connection with the replication master. Listens for a connection on the slavehost/port for DEFAULT_SOCKET_TIMEOUT milliseconds.
        Returns:
        true if a connection has been set up with the master, false if the connection attempt timed out.
        Throws:
        StandardException - if an unexpected exception occured that prevented a connection with the master.
      • handleDisconnect

        private void handleDisconnect​(java.lang.Exception e)
        Write the reason for the lost connection to the log (derby.log) and reconnect with the master. Once the network is up and running, a new LogReceiverThread is started. The method returns without doing anything if inReplicationSlaveMode=false, which means that stopSlave() has been called by another thread.
        Parameters:
        e - The reason the connection to the master was lost
      • isConnectedToMaster

        private boolean isConnectedToMaster()
        Check if the repliation network connection to the master is working
        Returns:
        true if the network connection is working, false otherwise
      • startLogReceiverThread

        private void startLogReceiverThread()
        Starts the LogReceiverThread that will listen for chunks of log records from the master and apply the log records to the local log file.
      • handleFatalException

        private void handleFatalException​(java.lang.Exception e)
        Handles fatal errors for slave replication functionality. These are errors that requires us to stop replication. Calling this method has the following effects: 1) Debug messages are written to the log file (usually derby.log) if ReplicationLogger#LOG_REPLICATION_MESSAGES is true. 2) If the network connection is up, the master is notified of the problem. 3) All slave replication functionality is stopped, and the database is then shut down without being booted. The method will return without doing anything if inReplicationSlaveMode=false, meaning that stopSlave has been called.
        Parameters:
        e - The fatal exception that is the reason for calling this method
      • teardownNetwork

        private void teardownNetwork()
      • getHostName

        private java.lang.String getHostName()
        Used to return the host name of the slave.
        Returns:
        a String containing the host name of the slave.
      • getPortNumber

        private int getPortNumber()
        Used to return the port number of the slave.
        Returns:
        an Integer that represents the port number of the slave.