net.openhft.chronicle.map

Interface EngineReplicationLangBytes

All Superinterfaces:

AutoCloseable, Closeable

public interface EngineReplicationLangBytes
extends Closeable

A simpler form of the replication interface used by Engine

*** PLEASE DON'T REFACTOR THIS WITHOUT FIRST CHANGING THE ENGINE CODE ***

Author:

Rob Austin.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	EngineReplicationLangBytes.EngineEntryCallback Implemented typically by a replicator, This interface provides the event, which will get called whenever a put() or remove() has occurred to the map
static interface	EngineReplicationLangBytes.EngineModificationIterator Holds a record of which entries have modification.
static interface	EngineReplicationLangBytes.EngineReplicationModificationNotifier notifies when there is a changed to the modification iterator

Method Summary

Methods

Modifier and Type	Method and Description
EngineReplicationLangBytes.EngineModificationIterator	acquireEngineModificationIterator(byte remoteIdentifier) Gets (if it does not exist, creates) an instance of ModificationIterator associated with a remote node, this weak associated is bound using the identifier.
byte	identifier() Provides the unique Identifier associated with this instance.
long	lastModificationTime(byte remoteIdentifier) Returns the timestamp of the last change from the specified remote node, already replicated to this host.
void	put(Bytes key, Bytes value, byte remoteIdentifier, long timestamp) inserts or updates the entry
void	remove(Bytes key, byte remoteIdentifier, long timestamp) marks the entry as removed
void	setLastModificationTime(byte identifier, long timestamp)

Methods inherited from interface java.io.Closeable

close

Method Detail

put

void put(Bytes key,
       Bytes value,
       byte remoteIdentifier,
       long timestamp)

inserts or updates the entry

Parameters:

key - the key of the entry

value - the value of the entry

remoteIdentifier - the identifier of the remote server

timestamp - the timestamp send from the remote server, this time stamp was the time the entry was removed

remove

void remove(Bytes key,
          byte remoteIdentifier,
          long timestamp)

marks the entry as removed

Parameters:

key - the key of the entry

remoteIdentifier - the identifier of the remote server

timestamp - the timestamp send from the remote server, this time stamp was the time the entry was removed

identifier

byte identifier()

Provides the unique Identifier associated with this instance.

An identifier is used to determine which replicating node made the change.

If two nodes update their map at the same time with different values, we have to deterministically resolve which update wins, because of eventual consistency both nodes should end up locally holding the same data. Although it is rare two remote nodes could receive an update to their maps at exactly the same time for the same key, we have to handle this edge case, its therefore important not to rely on timestamps alone to reconcile the updates. Typically the update with the newest timestamp should win, but in this example both timestamps are the same, and the decision made to one node should be identical to the decision made to the other. We resolve this simple dilemma by using a node identifier, each node will have a unique identifier, the update from the node with the smallest identifier wins.

Returns:

the unique Identifier associated with this map instance

acquireEngineModificationIterator

EngineReplicationLangBytes.EngineModificationIterator acquireEngineModificationIterator(byte remoteIdentifier)

Gets (if it does not exist, creates) an instance of ModificationIterator associated with a remote node, this weak associated is bound using the identifier.

Parameters:

remoteIdentifier - the identifier of the remote node

Returns:

the ModificationIterator dedicated for replication to the remote node with the given identifier

See Also:

identifier()

lastModificationTime

long lastModificationTime(byte remoteIdentifier)

Returns the timestamp of the last change from the specified remote node, already replicated to this host.

Used in conjunction with replication, to back fill data from a remote node. This node may have missed updates while it was not been running or connected via TCP.

Parameters:

remoteIdentifier - the identifier of the remote node to check last replicated update time from

Returns:

a timestamp of the last modification to an entry, or 0 if there are no entries.

See Also:

identifier()

setLastModificationTime

void setLastModificationTime(byte identifier,
                           long timestamp)