Package org.jgroups.protocols.pbcast

Class STREAMING_STATE_TRANSFER

java.lang.Object
org.jgroups.stack.Protocol
org.jgroups.protocols.pbcast.STREAMING_STATE_TRANSFER
public class STREAMING_STATE_TRANSFER extends Protocol
STREAMING_STATE_TRANSFER, as its name implies, allows a streaming state transfer between two channel instances.

Major advantage of this approach is that transferring application state to a joining member of a group does not entail loading of the complete application state into memory. Application state, for example, might be located entirely on some form of disk based storage. The default STATE_TRANSFER requires this state to be loaded entirely into memory before being transferred to a group member while STREAMING_STATE_TRANSFER does not. Thus STREAMING_STATE_TRANSFER protocol is able to transfer application state that is very large (>1Gb) without a likelihood of such transfer resulting in OutOfMemoryException.

STREAMING_STATE_TRANSFER allows use of either default channel transport or separate tcp sockets for state transfer. If firewalls are not a concern then separate tcp sockets should be used as they offer faster state transfer. Transport for state transfer is selected using use_default_transport boolean property.

Channel instance can be configured with either STREAMING_STATE_TRANSFER or STATE_TRANSFER but not both protocols at the same time.

In order to process streaming state transfer an application has to implement ExtendedMessageListener if it is using channel in a push style mode or it has to process StreamingSetStateEvent and StreamingGetStateEvent if it is using channel in a pull style mode.

Since:
2.4
Version:
$Id$
Author:
Vladimir Blagojevic
See Also:

  • Constructor Details

    • STREAMING_STATE_TRANSFER

      public STREAMING_STATE_TRANSFER()

  • Method Details

    • getName

      public final String getName()
      Specified by:
      getName in class Protocol

    • getNumberOfStateRequests

      public int getNumberOfStateRequests()

    • getNumberOfStateBytesSent

      public long getNumberOfStateBytesSent()

    • getAverageStateSize

      public double getAverageStateSize()

    • requiredDownServices

      public Vector<Integer> requiredDownServices()
      Description copied from class: Protocol
      List of events that are required to be answered by some layer below.
      Overrides:
      requiredDownServices in class Protocol
      Returns:
      Vector (of Integers)

    • resetStats

      public void resetStats()
      Overrides:
      resetStats in class Protocol

    • setProperties

      public boolean setProperties(Properties props)
      Description copied from class: Protocol
      Configures the protocol initially. A configuration string consists of name=value items, separated by a ';' (semicolon), e.g.:
       "loopback=false;unicast_inport=4444"
      Overrides:
      setProperties in class Protocol

    • init

      public void init() throws Exception
      Description copied from class: Protocol
      Called after instance has been created (null constructor) and before protocol is started. Properties are already set. Other protocols are not yet connected and events cannot yet be sent.
      Overrides:
      init in class Protocol
      Throws:
      Exception - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the channel constructor will throw an exception

    • start

      public void start() throws Exception
      Description copied from class: Protocol
      This method is called on a Channel.connect(String). Starts work. Protocols are connected and queues are ready to receive events. Will be called from bottom to top. This call will replace the START and START_OK events.
      Overrides:
      start in class Protocol
      Throws:
      Exception - Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, so Channel.connect(String) will throw an exception

    • stop

      public void stop()
      Description copied from class: Protocol
      This method is called on a Channel.disconnect(). Stops work (e.g. by closing multicast socket). Will be called from top to bottom. This means that at the time of the method invocation the neighbor protocol below is still working. This method will replace the STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that when this method is called all messages in the down queue will have been flushed
      Overrides:
      stop in class Protocol

    • up

      public Object up(Event evt)
      Description copied from class: Protocol
      An event was received from the layer below. Usually the current layer will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack using down_prot.down() or c) the event (or another event) is sent up the stack using up_prot.up().
      Overrides:
      up in class Protocol

    • down

      public Object down(Event evt)
      Description copied from class: Protocol
      An event is to be sent down the stack. The layer may want to examine its type and perform some action on it, depending on the event's type. If the event is a message MSG, then the layer may need to add a header to it (or do nothing at all) before sending it down the stack using down_prot.down(). In case of a GET_ADDRESS event (which tries to retrieve the stack's address from one of the bottom layers), the layer may need to send a new response event back up the stack using up_prot.up().
      Overrides:
      down in class Protocol