Field Detail

• serialVersionUID

  public static final long serialVersionUID

  The version number is determined based on the database version of the current database. This would help to establish if the master and the slave in replication are at compatible database versions.

  See Also:

  Constant Field Values

• message

  private java.lang.Object message

  This is the content of the replication message.

• type

  private int type

  The valid values for the type of the content of the message are listed below.

• TYPE_INITIATE_VERSION

  public static final int TYPE_INITIATE_VERSION

  used during the intial handshake between the master and the slave. The initial handshake helps to negotiate the message UIDs and send a appropriate error or acknowledgment. The object this message contains will be a Long. IMPORTANT: This constant must not be changed in future versions since we need it to decide slave/master version mismatch

  See Also:

  Constant Field Values

• TYPE_INITIATE_INSTANT

  public static final int TYPE_INITIATE_INSTANT

  Used during the intial handshake between the master and the slave. Messages of this type are used to ensure that master and slave have identical log files by checking that they will insert the next log record on the same byte position in the log. The object this message contains will be a Long.

  See Also:

  Constant Field Values

• TYPE_LOG

  public static final int TYPE_LOG

  This flag will be used for all messages that carry log records. The Object this message type contains will be a byte array. The content of the byte array is the log records in the binary form.

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  Constant Field Values

• TYPE_ACK

  public static final int TYPE_ACK

  This flag is used to send an acknowledgment of successful completion of a requested operation. It will however not be used to signify reception for every message transmission. The object this message type contains will be a String. The SQLState of the error message can be used here.

  See Also:

  Constant Field Values

• TYPE_ERROR

  public static final int TYPE_ERROR

  Indicates that the requested operation was not able to be completed successfully. The object this message type contains will be a String[] where the first length-1 fields are used as arguments to create the exception and the last field contains the SQLState. The SQLState is the last element in the Array, because this means that the whole Array can be used as input to the StandardException creator. The SQLState will be ignored by the exception creator because there is one argument too many. This way we don't have to make a copy of the received Array, containing all elements except the SQLState element.

  See Also:

  Constant Field Values

• TYPE_PING

  public static final int TYPE_PING

  A message used to check if the replication network is working. This message type has no object

  See Also:

  Constant Field Values

• TYPE_PONG

  public static final int TYPE_PONG

  A message sent as a response to a TYPE_PING message. This message type has no object

  See Also:

  Constant Field Values

• TYPE_STOP

  public static final int TYPE_STOP

  Used to send a stop replication signal to the slave. Since this is a control signal the object this message contains will be null.

  See Also:

  Constant Field Values

• TYPE_FAILOVER

  public static final int TYPE_FAILOVER

  Used to signal the slave that it must failover. The object associated with this message will be null.

  See Also:

  Constant Field Values

Constructor Detail

• ReplicationMessage

  public ReplicationMessage()

  public No args constructor required with Externalizable.

• ReplicationMessage

  public ReplicationMessage​(int type,
                            java.lang.Object message)

  Constructor used to set the type and message. This is used while creating messages for sending while readExternal is used on the receiving end.

  Parameters:

  type - The type of this message. Must be one of the message type constants of this class (TYPE_LOG, TYPE_ACK, TYPE_ERROR, TYPE_INITIATE).

  message - The message to be transmitted.

Method Detail

• getMessage

  public java.lang.Object getMessage()

  Used to get the actual message that is wrapped inside the ReplicationMessage object.

  Returns:

  The object contained in the message

• getType

  public int getType()

  Used to get the type of this ReplicationMessage.

  Returns:

  The type of the message.

• readExternal

  public void readExternal​(java.io.ObjectInput in)
                    throws java.io.IOException,
                           java.lang.ClassNotFoundException

  Used to restore the contents of this object.

  Specified by:

  readExternal in interface java.io.Externalizable

  Parameters:

  in - the stream to read data from in order to restore the object.

  Throws:

  java.io.IOException - If an exception occurs while reading from the InputStream.

  java.lang.ClassNotFoundException - Class of a serialized object cannot be found.

• writeExternal

  public void writeExternal​(java.io.ObjectOutput out)
                     throws java.io.IOException

  Used to save the contents of this Object.

  Specified by:

  writeExternal in interface java.io.Externalizable

  Parameters:

  out - the stream to write the object to.

  Throws:

  java.io.IOException - if an exception occurs while writing to the OutputStream.