com.sleepycat.je.rep
Class CommitPointConsistencyPolicy

java.lang.Object
  com.sleepycat.je.rep.CommitPointConsistencyPolicy

All Implemented Interfaces:

ReplicaConsistencyPolicy

public class CommitPointConsistencyPolicy
extends Object
implements ReplicaConsistencyPolicy

A consistency policy which ensures that the environment on a Replica node is at least as current as denoted by the specified CommitToken. This token represents a point in the serialized transaction schedule created by the master. In other words, this token is like a bookmark, representing a particular transaction commit in the replication stream. The Replica ensures that the commit identified by the CommitToken has been executed on this node before allowing the application's Environment.beginTransaction() operation on the Replica to proceed.

For example, suppose the application is a web application where a replicated group is implemented within a load balanced web server group. Each request to the web server consists of an update operation followed by read operations (say from the same client), The read operations naturally expect to see the data from the updates executed by the same request. However, the read operations might have been routed to a node that did not execute the update.

In such a case, the update request would generate a CommitToken, which would be resubmitted by the browser, along with subsequent read requests. The read request could be directed at any one of the available web servers by a load balancer. The node which executes the read request would create a CommitPointConsistencyPolicy with that CommitToken and use it at transaction begin. If the environment at the web server was already current (wrt the commit token), it could immediately execute the transaction and satisfy the request. If not, the "transaction begin" would stall until the Replica replay had caught up and the change was available at that web server.

Consistency policies are specified at either a per-transaction level through TransactionConfig.setConsistencyPolicy(com.sleepycat.je.ReplicaConsistencyPolicy) or as an replication node wide default through ReplicationConfig.setConsistencyPolicy(com.sleepycat.je.ReplicaConsistencyPolicy)

See Also:

CommitToken, Managing Consistency

Field Summary

static String

NAME The name:"CommitPointConsistencyPolicy" associated with this policy.

Constructor Summary

CommitPointConsistencyPolicy(CommitToken commitToken, long timeout, TimeUnit timeoutUnit)
Defines how current a Replica needs to be in terms of a specific transaction that was committed on the Master.

Method Summary

boolean	equals(Object obj)
CommitToken	getCommitToken() Return the CommitToken used to create this consistency policy.
String	getName() Returns the name:"CommitPointConsistencyPolicy", associated with this policy.
long	getTimeout(TimeUnit unit) Return the timeout specified when creating this consistency policy.
int	hashCode()
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

NAME

public static final String NAME

The name:"CommitPointConsistencyPolicy" associated with this policy. The name can be used when constructing policy property values for use in je.properties files.

See Also:

Constant Field Values

Constructor Detail

CommitPointConsistencyPolicy

public CommitPointConsistencyPolicy(CommitToken commitToken,
                                    long timeout,
                                    TimeUnit timeoutUnit)

Defines how current a Replica needs to be in terms of a specific transaction that was committed on the Master. A transaction on the Replica that uses this consistency policy is allowed to start only after the transaction identified by the commitToken has been committed on the Replica. The Environment.beginTransaction() will wait for at most timeout for the Replica to catch up. If the Replica has not caught up in this period, the beginTransaction() method will throw a ReplicaConsistencyException.

Parameters:

commitToken - the token identifying the transaction

timeout - the maximum amount of time that the transaction start will wait to allow the Replica to catch up.

timeoutUnit - the TimeUnit for the timeout parameter.

Throws:

IllegalArgumentException - if the commitToken or timeoutUnit is null.

Method Detail

getName

public String getName()

Returns the name:"CommitPointConsistencyPolicy", associated with this policy.

Specified by:

getName in interface ReplicaConsistencyPolicy

See Also:

NAME

getCommitToken

public CommitToken getCommitToken()

Return the CommitToken used to create this consistency policy.

Returns:

the CommitToken used to create this consistency policy.

getTimeout

public long getTimeout(TimeUnit unit)

Return the timeout specified when creating this consistency policy.

Specified by:

getTimeout in interface ReplicaConsistencyPolicy

Parameters:

unit - the TimeUnit of the returned value.

Returns:

the timeout specified when creating this consistency policy

hashCode

public int hashCode()

Overrides:

hashCode in class Object

See Also:

Object.hashCode()

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

See Also:

Object.equals(java.lang.Object)

toString

public String toString()

Overrides:

toString in class Object