com.bigdata.quorum

Class QuorumStateChangeListenerBase

java.lang.Object

com.bigdata.quorum.QuorumStateChangeListenerBase

All Implemented Interfaces:

QuorumStateChangeListener

Direct Known Subclasses:

QuorumCommitImpl, QuorumReadImpl

public class QuorumStateChangeListenerBase
extends Object
implements QuorumStateChangeListener

QuorumStateChangeListener provides NOP method implementations.

Version:

$Id$

Author:

Bryan Thompson

Constructor Summary

Constructors

Constructor and Description
QuorumStateChangeListenerBase()

Method Summary

Methods

Modifier and Type	Method and Description
void	consensus(long lastCommitTime) Invoked when a consensus has been achieved among (k+1)/2 services concerning a shared lastCommitTime (really, this is not a consensus but a simple majority).
void	lostConsensus() Invoked when the consensus is lost.
void	memberAdd() Invoked when this service is added as a quorum member.
void	memberRemove() Invoked when this service is removed as a quorum member.
void	pipelineAdd() Invoked when this service is added to the write pipeline.
void	pipelineChange(UUID oldDownStreamId, UUID newDownStreamId) Invoked for this service when the downstream service in the write pipeline has changed.
void	pipelineElectedLeader() Invoked for this service when the service is already in the pipeline and this service becomes the first service in the write pipeline because all previous services in the pipeline order have been removed from the pipeline (failover into the leader position).
void	pipelineRemove() Invoked when this service is removed from the write pipeline.
void	pipelineUpstreamChange() Invoked for this service when the upstream service in the write pipeline has been removed.
void	quorumBreak() Invoked when a quorum breaks.
void	quorumMeet(long token, UUID leaderId) Invoked when a quorum meets.
void	serviceJoin() Invoked when this service joins the quorum.
void	serviceLeave() Invoked when this service leaves the quorum.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

QuorumStateChangeListenerBase

public QuorumStateChangeListenerBase()

Method Detail

memberAdd

public void memberAdd()

Description copied from interface: QuorumStateChangeListener

Invoked when this service is added as a quorum member.

Specified by:

memberAdd in interface QuorumStateChangeListener

memberRemove

public void memberRemove()

Description copied from interface: QuorumStateChangeListener

Invoked when this service is removed as a quorum member.

Specified by:

memberRemove in interface QuorumStateChangeListener

pipelineAdd

public void pipelineAdd()

Description copied from interface: QuorumStateChangeListener

Invoked when this service is added to the write pipeline. The service always enters at the of the pipeline.

Specified by:

pipelineAdd in interface QuorumStateChangeListener

pipelineRemove

public void pipelineRemove()

Description copied from interface: QuorumStateChangeListener

Invoked when this service is removed from the write pipeline.

Specified by:

pipelineRemove in interface QuorumStateChangeListener

pipelineElectedLeader

public void pipelineElectedLeader()

Description copied from interface: QuorumStateChangeListener

Invoked for this service when the service is already in the pipeline and this service becomes the first service in the write pipeline because all previous services in the pipeline order have been removed from the pipeline (failover into the leader position).

Specified by:

pipelineElectedLeader in interface QuorumStateChangeListener

pipelineChange

public void pipelineChange(UUID oldDownStreamId,
                  UUID newDownStreamId)

Description copied from interface: QuorumStateChangeListener

Invoked for this service when the downstream service in the write pipeline has changed. Services always enter at the end of the write pipeline, but may be removed at any position in the write pipeline.

Specified by:

pipelineChange in interface QuorumStateChangeListener

pipelineUpstreamChange

public void pipelineUpstreamChange()

Description copied from interface: QuorumStateChangeListener

Invoked for this service when the upstream service in the write pipeline has been removed. This hook provides an opportunity for this service to close out its connection with the old upstream service and to prepare to establish a new connection with the new downstream service.

Specified by:

pipelineUpstreamChange in interface QuorumStateChangeListener

consensus

public void consensus(long lastCommitTime)

Description copied from interface: QuorumStateChangeListener

Invoked when a consensus has been achieved among (k+1)/2 services concerning a shared lastCommitTime (really, this is not a consensus but a simple majority). This message is sent to each member service regardless of whether or not they participated in the consensus.

Once a consensus has been reached, each QuorumMember which agrees on that lastCommitTime MUST do a QuorumStateChangeListener.serviceJoin() before the quorum will meet. The first quorum member to do a service join will be elected the leader. The remaining services to do a service join will be elected followers.

Specified by:

consensus in interface QuorumStateChangeListener

Parameters:

lastCommitTime - The last commit time around which a consensus was established.

See Also:

QuorumStateChangeListener.serviceJoin(), #electedLeader(long), #electedFollower(long), QuorumStateChangeListener.lostConsensus()

lostConsensus

public void lostConsensus()

Description copied from interface: QuorumStateChangeListener

Invoked when the consensus is lost. Services do not withdraw their cast votes until a quorum breaks and a new consensus needs to be established. This message is sent to each member service regardless of whether or not they participated in the consensus.

Specified by:

lostConsensus in interface QuorumStateChangeListener

See Also:

QuorumStateChangeListener.consensus(long)

quorumBreak

public void quorumBreak()

Description copied from interface: QuorumStateChangeListener

Invoked when a quorum breaks. The service MUST handle handle this event by (a) doing an abort() which will any buffered writes and reload their current root block; and (b) casting a vote for their current commit time. Once a consensus is reached on the current commit time, services will be joined in the vote order, a new leader will be elected, and the quorum will meet again. This message is sent to all member services, regardless of whether they were joined with the met quorum.

Specified by:

quorumBreak in interface QuorumStateChangeListener

serviceJoin

public void serviceJoin()

Description copied from interface: QuorumStateChangeListener

Invoked when this service joins the quorum.

Specified by:

serviceJoin in interface QuorumStateChangeListener

serviceLeave

public void serviceLeave()

Description copied from interface: QuorumStateChangeListener

Invoked when this service leaves the quorum.

Specified by:

serviceLeave in interface QuorumStateChangeListener

quorumMeet

public void quorumMeet(long token,
              UUID leaderId)

Description copied from interface: QuorumStateChangeListener

Invoked when a quorum meets. The state of the met quorum can be queried using the token. Quorum members can use this to decide whether they are the leader (using #isLeader(long), joined as a follower (using #isFollower(long)), or do not participate in the quorum (this message is sent to all quorum members, so this service might not be part of the met qourum).

The following pre-conditions will be satisfied before this message is sent to the QuorumMember:

• There will be at least (k+1)/2 services which have voted for the same lastCommitTime.
• There will be at (k+1)/2 services joined with the quorum. The join order will be the same as the Quorum.getVotes() for the services which voted for the lastCommitTime
around which a consensus was formed.
• If this quorum member is joined with the quorum it will have observed its own QuorumStateChangeListener.memberAdd(), QuorumStateChangeListener.pipelineAdd(), QuorumStateChangeListener.consensus(long), and QuorumStateChangeListener.serviceJoin() events.
• The joined services will be arranged in a write pipeline, with the leader at the head of that pipeline.

When control returns from this method, the following post-conditions should be true:

• The service should be prepared to accept reads.
• If the service was elected as the quorum leader, then it should be prepared to accept writes.

If the QuorumMember is joined with the quorum but it can not satisfy these post-conditions, then it must leave the Quorum.

Specified by:

quorumMeet in interface QuorumStateChangeListener

Parameters:

token - The newly assigned quorum token.

leaderId - The UUID of the service which was elected to be the quorum leader. This information is only valid for the scope of the accompanying quorum token. (The leaderId may be obtained from #getLeader(long) at any time for a met quorum.)