Package com.datastax.driver.core.policies

Class ConstantSpeculativeExecutionPolicy

java.lang.Object

com.datastax.driver.core.policies.ConstantSpeculativeExecutionPolicy

All Implemented Interfaces:

SpeculativeExecutionPolicy

public class ConstantSpeculativeExecutionPolicy
extends Object
implements SpeculativeExecutionPolicy

A SpeculativeExecutionPolicy that schedules a given number of speculative executions, separated by a fixed delay.

Nested Class Summary

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

SpeculativeExecutionPolicy.SpeculativeExecutionPlan

Constructor Summary

Constructors

Constructor	Description
ConstantSpeculativeExecutionPolicy(long constantDelayMillis, int maxSpeculativeExecutions)	Builds a new instance.

Method Summary

Modifier and Type	Method	Description
void	close()	Gets invoked at cluster shutdown.
long	getConstantDelayMillis()	The delay between each speculative execution, as specified at instantiation.
int	getMaxSpeculativeExecutions()	The number of speculative executions this policy schedules for a request, as specified at instantiation.
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

ConstantSpeculativeExecutionPolicy

public ConstantSpeculativeExecutionPolicy(long constantDelayMillis,
                                          int maxSpeculativeExecutions)

Builds a new instance.

Parameters:

constantDelayMillis - the delay between each speculative execution. Must be >= 0. A zero delay means it should immediately send `maxSpeculativeExecutions` requests along with the original request.

maxSpeculativeExecutions - the number of speculative executions. Must be strictly positive.

Throws:

IllegalArgumentException - if one of the arguments does not respect the preconditions above.

Method Detail

getMaxSpeculativeExecutions

@Beta
public int getMaxSpeculativeExecutions()

The number of speculative executions this policy schedules for a request, as specified at instantiation. This does not include the initial, normal request.

Returns:

the number of speculative executions, always strictly positive.

getConstantDelayMillis

@Beta
public long getConstantDelayMillis()

The delay between each speculative execution, as specified at instantiation. Zero means all executions are sent immediately, along with the original request.

Returns:

the delay in milliseconds, never negative.

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