com.datastax.driver.core.policies

Class PercentileSpeculativeExecutionPolicy

java.lang.Object

com.datastax.driver.core.policies.PercentileSpeculativeExecutionPolicy

All Implemented Interfaces:

SpeculativeExecutionPolicy

@Beta
public class PercentileSpeculativeExecutionPolicy
extends Object
implements SpeculativeExecutionPolicy

A policy that triggers speculative executions when the request to the current host is above a given percentile.

This class uses a PerHostPercentileTracker that must be registered with the cluster instance:

 PerHostPercentileTracker tracker = PerHostPercentileTracker
     .builderWithHighestTrackableLatencyMillis(15000)
     .build();
 PercentileSpeculativeExecutionPolicy policy = new PercentileSpeculativeExecutionPolicy(tracker, 99.0, 2);
 cluster = Cluster.builder()
     .addContactPoint("127.0.0.1")
     .withSpeculativeExecutionPolicy(policy)
     .build();
 cluster.register(tracker);
 

You must register the tracker with the cluster yourself (as shown on the last line above), this class will not do it itself.

This class is currently provided as a beta preview: it hasn't been extensively tested yet, and the API is still subject to change.

Nested Class Summary

Nested classes/interfaces inherited from interface com.datastax.driver.core.policies.SpeculativeExecutionPolicy

SpeculativeExecutionPolicy.SpeculativeExecutionPlan

Constructor Summary

Constructors

Constructor and Description
PercentileSpeculativeExecutionPolicy(PerHostPercentileTracker percentileTracker, double percentile, int maxSpeculativeExecutions) Builds a new instance.

Method Summary

Modifier and Type	Method and Description
void	close() Gets invoked at cluster shutdown.
void	init(Cluster cluster) Gets invoked at cluster startup.
SpeculativeExecutionPolicy.SpeculativeExecutionPlan	newPlan(String loggedKeyspace, Statement statement) Returns the plan to use for a new query.

Methods inherited from class java.lang.Object

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

Constructor Detail

PercentileSpeculativeExecutionPolicy

public PercentileSpeculativeExecutionPolicy(PerHostPercentileTracker percentileTracker,
                                            double percentile,
                                            int maxSpeculativeExecutions)

Builds a new instance.

Parameters:

percentileTracker - the component that will record latencies. Note that this policy doesn't register it with the Cluster, you must do it yourself (see the code example in this class's Javadoc).

percentile - the percentile that a request's latency must fall into to be considered slow (ex: 99.0).

maxSpeculativeExecutions - the maximum number of speculative executions that will be triggered for a given request (this does not include the initial, normal request). Must be strictly positive.

Method Detail

newPlan

public SpeculativeExecutionPolicy.SpeculativeExecutionPlan newPlan(String loggedKeyspace,
                                                                   Statement statement)

Description copied from interface: SpeculativeExecutionPolicy

Returns the plan to use for a new query.

Specified by:

newPlan in interface SpeculativeExecutionPolicy

Parameters:

loggedKeyspace - the currently logged keyspace (the one set through either Cluster.connect(String) or by manually doing a USE query) for the session on which this plan need to be built. This can be null if the corresponding session has no keyspace logged in.

statement - the query for which to build a plan.

Returns:

the plan.

init

public void init(Cluster cluster)

Description copied from interface: SpeculativeExecutionPolicy

Gets invoked at cluster startup.

Specified by:

init in interface SpeculativeExecutionPolicy

Parameters:

cluster - the cluster that this policy is associated with.

close

public void close()

Description copied from interface: SpeculativeExecutionPolicy

Gets invoked at cluster shutdown.

This gives the policy the opportunity to perform some cleanup, for instance stop threads that it might have started.

Specified by:

close in interface SpeculativeExecutionPolicy