Class ReplicationMessage
- java.lang.Object
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- org.apache.derby.impl.store.replication.net.ReplicationMessage
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- All Implemented Interfaces:
java.io.Externalizable
,java.io.Serializable
public class ReplicationMessage extends java.lang.Object implements java.io.Externalizable
This message is used for the communication between the master and the slave during Replication. The message is composed of a type flag and corresponding object. Each type flag indicating the type of the content bundled inside the message.- See Also:
- Serialized Form
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Field Summary
Fields Modifier and Type Field Description private java.lang.Object
message
This is the content of the replication message.static long
serialVersionUID
The version number is determined based on the database version of the current database.private int
type
The valid values for the type of the content of the message are listed below.static int
TYPE_ACK
This flag is used to send an acknowledgment of successful completion of a requested operation.static int
TYPE_ERROR
Indicates that the requested operation was not able to be completed successfully.static int
TYPE_FAILOVER
Used to signal the slave that it must failover.static int
TYPE_INITIATE_INSTANT
Used during the intial handshake between the master and the slave.static int
TYPE_INITIATE_VERSION
used during the intial handshake between the master and the slave.static int
TYPE_LOG
This flag will be used for all messages that carry log records.static int
TYPE_PING
A message used to check if the replication network is working.static int
TYPE_PONG
A message sent as a response to a TYPE_PING message.static int
TYPE_STOP
Used to send a stop replication signal to the slave.
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Constructor Summary
Constructors Constructor Description ReplicationMessage()
public No args constructor required with Externalizable.ReplicationMessage(int type, java.lang.Object message)
Constructor used to set thetype
andmessage
.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description java.lang.Object
getMessage()
Used to get the actual message that is wrapped inside the ReplicationMessage object.int
getType()
Used to get the type of thisReplicationMessage
.void
readExternal(java.io.ObjectInput in)
Used to restore the contents of this object.void
writeExternal(java.io.ObjectOutput out)
Used to save the contents of this Object.
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Field Detail
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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
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message
private java.lang.Object message
This is the content of the replication message.
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type
private int type
The valid values for the type of the content of the message are listed below.
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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 aLong
. 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
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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 aLong
.- See Also:
- Constant Field Values
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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 abyte
array. The content of the byte array is the log records in the binary form.- See Also:
- Constant Field Values
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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 aString
. The SQLState of the error message can be used here.- See Also:
- Constant Field Values
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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 aString[]
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
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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
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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
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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
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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
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Constructor Detail
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ReplicationMessage
public ReplicationMessage()
public No args constructor required with Externalizable.
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ReplicationMessage
public ReplicationMessage(int type, java.lang.Object message)
Constructor used to set thetype
andmessage
. 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.
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Method Detail
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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
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getType
public int getType()
Used to get the type of thisReplicationMessage
.- Returns:
- The type of the message.
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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 interfacejava.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 theInputStream
.java.lang.ClassNotFoundException
- Class of a serialized object cannot be found.
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writeExternal
public void writeExternal(java.io.ObjectOutput out) throws java.io.IOException
Used to save the contents of this Object.- Specified by:
writeExternal
in interfacejava.io.Externalizable
- Parameters:
out
- the stream to write the object to.- Throws:
java.io.IOException
- if an exception occurs while writing to theOutputStream
.
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