org.neo4j.causalclustering.core.state.machines.locks

Class LeaderOnlyLockManager

java.lang.Object

org.neo4j.causalclustering.core.state.machines.locks.LeaderOnlyLockManager

All Implemented Interfaces:

org.neo4j.kernel.impl.locking.Locks

public class LeaderOnlyLockManager
extends Object
implements org.neo4j.kernel.impl.locking.Locks

Each member of the cluster uses its own LeaderOnlyLockManager which wraps a local Locks manager. The validity of local lock managers is synchronized by using a token which gets requested by each server as necessary and if the request is granted then the associated id can be used to identify a unique lock session in the cluster.

The fundamental strategy is to only allow locks on the leader. This has the benefit of minimizing the synchronization to only concern the single token but it also means that non-leaders should not even attempt to request the token or significant churn of this single resource will lead to a high level of aborted transactions.

The token requests carry a candidate id and they get ordered with respect to the transactions in the consensus machinery. The latest request which gets accepted (see ReplicatedTransactionStateMachine) defines the currently valid lock session id in this ordering. Each transaction that uses locking gets marked with a lock session id that was valid at the time of acquiring it, but by the time a transaction commits it might no longer be valid, which in such case would lead to the transaction being rejected and failed.

The ReplicatedLockTokenStateMachine handles the token requests and considers only one to be valid at a time. Meanwhile, ReplicatedTransactionStateMachine rejects any transactions that get committed under an invalid token.

Nested Class Summary

Nested classes/interfaces inherited from interface org.neo4j.kernel.impl.locking.Locks

org.neo4j.kernel.impl.locking.Locks.Client, org.neo4j.kernel.impl.locking.Locks.Factory, org.neo4j.kernel.impl.locking.Locks.Visitor

Field Summary

Fields

Modifier and Type	Field and Description
static String	LOCK_NOT_ON_LEADER_ERROR_MESSAGE

Constructor Summary

Constructors

Constructor and Description
LeaderOnlyLockManager(MemberId myself, Replicator replicator, LeaderLocator leaderLocator, org.neo4j.kernel.impl.locking.Locks localLocks, ReplicatedLockTokenStateMachine lockTokenStateMachine)

Method Summary

Modifier and Type	Method and Description
void	accept(org.neo4j.kernel.impl.locking.Locks.Visitor visitor)
void	close()
org.neo4j.kernel.impl.locking.Locks.Client	newClient()

Methods inherited from class java.lang.Object

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

Field Detail

LOCK_NOT_ON_LEADER_ERROR_MESSAGE

public static final String LOCK_NOT_ON_LEADER_ERROR_MESSAGE

See Also:

Constant Field Values

Constructor Detail

LeaderOnlyLockManager

public LeaderOnlyLockManager(MemberId myself,
                             Replicator replicator,
                             LeaderLocator leaderLocator,
                             org.neo4j.kernel.impl.locking.Locks localLocks,
                             ReplicatedLockTokenStateMachine lockTokenStateMachine)

Method Detail

newClient

public org.neo4j.kernel.impl.locking.Locks.Client newClient()

Specified by:

newClient in interface org.neo4j.kernel.impl.locking.Locks

accept

public void accept(org.neo4j.kernel.impl.locking.Locks.Visitor visitor)

Specified by:

accept in interface org.neo4j.kernel.impl.locking.Locks

close

public void close()

Specified by:

close in interface org.neo4j.kernel.impl.locking.Locks