org.apache.cassandra.service

Class AbstractReadExecutor

java.lang.Object

org.apache.cassandra.service.AbstractReadExecutor

public abstract class AbstractReadExecutor
extends java.lang.Object

Sends a read request to the replicas needed to satisfy a given ConsistencyLevel. Optionally, may perform additional requests to provide redundancy against replica failure: AlwaysSpeculatingReadExecutor will always send a request to one extra replica, while SpeculatingReadExecutor will wait until it looks like the original request is in danger of timing out before performing extra reads.

Field Summary

Fields

Modifier and Type	Field and Description
protected ReadCommand	command
protected ReadCallback<ReadResponse,Row>	handler
protected RowDigestResolver	resolver
protected java.util.List<java.net.InetAddress>	targetReplicas
protected TraceState	traceState

Method Summary

Methods

Modifier and Type	Method and Description
abstract void	executeAsync() send the initial set of requests
Row	get() wait for an answer.
abstract java.util.Collection<java.net.InetAddress>	getContactedReplicas() Get the replicas involved in the [finished] request.
static AbstractReadExecutor	getReadExecutor(ReadCommand command, ConsistencyLevel consistencyLevel)
protected void	makeDataRequests(java.lang.Iterable<java.net.InetAddress> endpoints)
protected void	makeDigestRequests(java.lang.Iterable<java.net.InetAddress> endpoints)
abstract void	maybeTryAdditionalReplicas() Perform additional requests if it looks like the original will time out.

Methods inherited from class java.lang.Object

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

Field Detail

command

protected final ReadCommand command

targetReplicas

protected final java.util.List<java.net.InetAddress> targetReplicas

resolver

protected final RowDigestResolver resolver

handler

protected final ReadCallback<ReadResponse,Row> handler

traceState

protected final TraceState traceState

Method Detail

makeDataRequests

protected void makeDataRequests(java.lang.Iterable<java.net.InetAddress> endpoints)

makeDigestRequests

protected void makeDigestRequests(java.lang.Iterable<java.net.InetAddress> endpoints)

maybeTryAdditionalReplicas

public abstract void maybeTryAdditionalReplicas()

Perform additional requests if it looks like the original will time out. May block while it waits to see if the original requests are answered first.

getContactedReplicas

public abstract java.util.Collection<java.net.InetAddress> getContactedReplicas()

Get the replicas involved in the [finished] request.

Returns:

target replicas + the extra replica, *IF* we speculated.

executeAsync

public abstract void executeAsync()

send the initial set of requests

get

public Row get()
        throws ReadFailureException,
               ReadTimeoutException,
               DigestMismatchException

wait for an answer. Blocks until success or timeout, so it is caller's responsibility to call maybeTryAdditionalReplicas first.

Throws:

ReadFailureException

ReadTimeoutException

DigestMismatchException

getReadExecutor

public static AbstractReadExecutor getReadExecutor(ReadCommand command,
                                   ConsistencyLevel consistencyLevel)
                                            throws UnavailableException

Returns:

an executor appropriate for the configured speculative read policy

Throws:

UnavailableException