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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.cassandra.service.paxos;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.function.Consumer;
import com.google.common.annotations.VisibleForTesting;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.db.TypeSizes;
import org.apache.cassandra.exceptions.RequestFailureReason;
import org.apache.cassandra.io.IVersionedSerializer;
import org.apache.cassandra.io.util.DataInputPlus;
import org.apache.cassandra.io.util.DataOutputPlus;
import org.apache.cassandra.locator.InetAddressAndPort;
import org.apache.cassandra.net.IVerbHandler;
import org.apache.cassandra.net.Message;
import org.apache.cassandra.net.MessagingService;
import org.apache.cassandra.service.paxos.Commit.Proposal;
import org.apache.cassandra.utils.concurrent.ConditionAsConsumer;
import static java.util.Collections.emptyMap;
import static org.apache.cassandra.exceptions.RequestFailureReason.UNKNOWN;
import static org.apache.cassandra.net.Verb.PAXOS2_PROPOSE_REQ;
import static org.apache.cassandra.service.paxos.PaxosPropose.Superseded.SideEffects.NO;
import static org.apache.cassandra.service.paxos.PaxosPropose.Superseded.SideEffects.MAYBE;
import static org.apache.cassandra.utils.Clock.Global.nanoTime;
import static org.apache.cassandra.utils.concurrent.ConditionAsConsumer.newConditionAsConsumer;
/**
* In waitForNoSideEffect mode, we will not return failure to the caller until
* we have received a complete set of refusal responses, or at least one accept,
* indicating (respectively) that we have had no side effect, or that we cannot
* know if we our proposal produced a side effect.
*/
public class PaxosPropose> extends PaxosRequestCallback
{
private static final Logger logger = LoggerFactory.getLogger(PaxosPropose.class);
public static final RequestHandler requestHandler = new RequestHandler();
public static final RequestSerializer requestSerializer = new RequestSerializer();
public static final ResponseSerializer responseSerializer = new ResponseSerializer();
/**
* Represents the current status of a propose action: it is a status rather than a result,
* as the result may be unknown without sufficient responses (though in most cases it is final status).
*/
static class Status
{
enum Outcome { SUCCESS, SUPERSEDED, MAYBE_FAILURE }
final Outcome outcome;
Status(Outcome outcome)
{
this.outcome = outcome;
}
Superseded superseded() { return (Superseded) this; }
Paxos.MaybeFailure maybeFailure() { return ((MaybeFailure) this).info; }
public String toString() { return "Success"; }
}
static class Superseded extends Status
{
enum SideEffects { NO, MAYBE }
final Ballot by;
final SideEffects hadSideEffects;
Superseded(Ballot by, SideEffects hadSideEffects)
{
super(Outcome.SUPERSEDED);
this.by = by;
this.hadSideEffects = hadSideEffects;
}
public String toString() { return "Superseded(" + by + ',' + hadSideEffects + ')'; }
}
private static class MaybeFailure extends Status
{
final Paxos.MaybeFailure info;
MaybeFailure(Paxos.MaybeFailure info)
{
super(Outcome.MAYBE_FAILURE);
this.info = info;
}
public String toString() { return info.toString(); }
}
private static final Status success = new Status(Status.Outcome.SUCCESS);
private static final AtomicLongFieldUpdater responsesUpdater = AtomicLongFieldUpdater.newUpdater(PaxosPropose.class, "responses");
private static final AtomicReferenceFieldUpdater supersededByUpdater = AtomicReferenceFieldUpdater.newUpdater(PaxosPropose.class, Ballot.class, "supersededBy");
@VisibleForTesting public static final long ACCEPT_INCREMENT = 1;
private static final int REFUSAL_SHIFT = 21;
@VisibleForTesting public static final long REFUSAL_INCREMENT = 1L << REFUSAL_SHIFT;
private static final int FAILURE_SHIFT = 42;
@VisibleForTesting public static final long FAILURE_INCREMENT = 1L << FAILURE_SHIFT;
private static final long MASK = (1L << REFUSAL_SHIFT) - 1L;
private final Proposal proposal;
/** Wait until we know if we may have had side effects */
private final boolean waitForNoSideEffect;
/** Number of contacted nodes */
final int participants;
/** Number of accepts required */
final int required;
/** Invoke on reaching a terminal status */
final OnDone onDone;
/**
* bit 0-20: accepts
* bit 21-41: refusals/errors
* bit 42-62: timeouts
* bit 63: ambiguous signal bit (i.e. those states that cannot be certain to signal uniquely flip this bit to take signal responsibility)
*
* {@link #accepts}
* {@link #refusals}
* {@link #failures}
* {@link #notAccepts} (timeouts/errors+refusals)
*/
private volatile long responses;
/** The newest superseding ballot from a refusal; only returned to the caller if we fail to reach a quorum */
private volatile Ballot supersededBy;
private PaxosPropose(Proposal proposal, int participants, int required, boolean waitForNoSideEffect, OnDone onDone)
{
this.proposal = proposal;
assert required > 0;
this.waitForNoSideEffect = waitForNoSideEffect;
this.participants = participants;
this.required = required;
this.onDone = onDone;
}
/**
* Submit the proposal for commit with all replicas, and return an object that can be waited on synchronously for the result,
* or for the present status if the time elapses without a final result being reached.
* @param waitForNoSideEffect if true, on failure we will wait until we can say with certainty there are no side effects
* or until we know we will never be able to determine this with certainty
*/
static Paxos.Async propose(Proposal proposal, Paxos.Participants participants, boolean waitForNoSideEffect)
{
if (waitForNoSideEffect && proposal.update.isEmpty())
waitForNoSideEffect = false; // by definition this has no "side effects" (besides linearizing the operation)
// to avoid unnecessary object allocations we extend PaxosPropose to implements Paxos.Async
class Async extends PaxosPropose> implements Paxos.Async
{
private Async(Proposal proposal, int participants, int required, boolean waitForNoSideEffect)
{
super(proposal, participants, required, waitForNoSideEffect, newConditionAsConsumer());
}
public Status awaitUntil(long deadline)
{
try
{
onDone.awaitUntil(deadline);
}
catch (InterruptedException e)
{
Thread.currentThread().interrupt();
return new MaybeFailure(new Paxos.MaybeFailure(true, participants, required, 0, emptyMap()));
}
return status();
}
}
Async propose = new Async(proposal, participants.sizeOfPoll(), participants.sizeOfConsensusQuorum, waitForNoSideEffect);
propose.start(participants);
return propose;
}
static > T propose(Proposal proposal, Paxos.Participants participants, boolean waitForNoSideEffect, T onDone)
{
if (waitForNoSideEffect && proposal.update.isEmpty())
waitForNoSideEffect = false; // by definition this has no "side effects" (besides linearizing the operation)
PaxosPropose propose = new PaxosPropose<>(proposal, participants.sizeOfPoll(), participants.sizeOfConsensusQuorum, waitForNoSideEffect, onDone);
propose.start(participants);
return onDone;
}
void start(Paxos.Participants participants)
{
Message message = Message.out(PAXOS2_PROPOSE_REQ, new Request(proposal));
boolean executeOnSelf = false;
for (int i = 0, size = participants.sizeOfPoll(); i < size ; ++i)
{
InetAddressAndPort destination = participants.voter(i);
logger.trace("{} to {}", proposal, destination);
if (shouldExecuteOnSelf(destination)) executeOnSelf = true;
else MessagingService.instance().sendWithCallback(message, destination, this);
}
if (executeOnSelf)
PAXOS2_PROPOSE_REQ.stage.execute(() -> executeOnSelf(proposal));
}
/**
* @return the result as of now; unless the result is definitive, it is only a snapshot of the present incomplete status
*/
Status status()
{
long responses = this.responses;
if (isSuccessful(responses))
return success;
if (!canSucceed(responses) && supersededBy != null)
{
Superseded.SideEffects sideEffects = hasNoSideEffects(responses) ? NO : MAYBE;
return new Superseded(supersededBy, sideEffects);
}
return new MaybeFailure(new Paxos.MaybeFailure(participants, required, accepts(responses), failureReasonsAsMap()));
}
private void executeOnSelf(Proposal proposal)
{
executeOnSelf(proposal, RequestHandler::execute);
}
public void onResponse(Response response, InetAddressAndPort from)
{
if (logger.isTraceEnabled())
logger.trace("{} for {} from {}", response, proposal, from);
Ballot supersededBy = response.supersededBy;
if (supersededBy != null)
supersededByUpdater.accumulateAndGet(this, supersededBy, (a, b) -> a == null ? b : b.uuidTimestamp() > a.uuidTimestamp() ? b : a);
long increment = supersededBy == null
? ACCEPT_INCREMENT
: REFUSAL_INCREMENT;
update(increment);
}
@Override
public void onFailure(InetAddressAndPort from, RequestFailureReason reason)
{
if (logger.isTraceEnabled())
logger.trace("{} {} failure from {}", proposal, reason, from);
super.onFailure(from, reason);
update(FAILURE_INCREMENT);
}
private void update(long increment)
{
long responses = responsesUpdater.addAndGet(this, increment);
if (shouldSignal(responses))
signalDone();
}
// returns true at most once for a given PaxosPropose, so we do not propagate a signal more than once
private boolean shouldSignal(long responses)
{
return shouldSignal(responses, required, participants, waitForNoSideEffect, responsesUpdater, this);
}
@VisibleForTesting
public static boolean shouldSignal(long responses, int required, int participants, boolean waitForNoSideEffect, AtomicLongFieldUpdater responsesUpdater, T update)
{
if (responses <= 0L) // already signalled via ambiguous signal bit
return false;
if (!isSuccessful(responses, required))
{
if (canSucceed(responses, required, participants))
return false;
if (waitForNoSideEffect && !hasPossibleSideEffects(responses))
return hasNoSideEffects(responses, participants);
}
return responsesUpdater.getAndUpdate(update, x -> x | Long.MIN_VALUE) >= 0L;
}
private void signalDone()
{
if (onDone != null)
onDone.accept(status());
}
private boolean isSuccessful(long responses)
{
return isSuccessful(responses, required);
}
private static boolean isSuccessful(long responses, int required)
{
return accepts(responses) >= required;
}
private boolean canSucceed(long responses)
{
return canSucceed(responses, required, participants);
}
private static boolean canSucceed(long responses, int required, int participants)
{
return refusals(responses) == 0 && required <= participants - failures(responses);
}
// Note: this is only reliable if !failFast
private boolean hasNoSideEffects(long responses)
{
return hasNoSideEffects(responses, participants);
}
private static boolean hasNoSideEffects(long responses, int participants)
{
return refusals(responses) == participants;
}
private static boolean hasPossibleSideEffects(long responses)
{
return accepts(responses) + failures(responses) > 0;
}
/** {@link #responses} */
private static int accepts(long responses)
{
return (int) (responses & MASK);
}
/** {@link #responses} */
private static int notAccepts(long responses)
{
return failures(responses) + refusals(responses);
}
/** {@link #responses} */
private static int refusals(long responses)
{
return (int) ((responses >>> REFUSAL_SHIFT) & MASK);
}
/** {@link #responses} */
private static int failures(long responses)
{
return (int) ((responses >>> FAILURE_SHIFT) & MASK);
}
/**
* A Proposal to submit to another node
*/
static class Request
{
final Proposal proposal;
Request(Proposal proposal)
{
this.proposal = proposal;
}
public String toString()
{
return proposal.toString("Propose");
}
}
/**
* The response to a proposal, indicating success (if {@code supersededBy == null},
* or failure, alongside the ballot that beat us
*/
static class Response
{
final Ballot supersededBy;
Response(Ballot supersededBy)
{
this.supersededBy = supersededBy;
}
public String toString() { return supersededBy == null ? "Accept" : "RejectProposal(supersededBy=" + supersededBy + ')'; }
}
/**
* The proposal request handler, i.e. receives a proposal from a peer and responds with either acccept/reject
*/
public static class RequestHandler implements IVerbHandler
{
@Override
public void doVerb(Message message)
{
Response response = execute(message.payload.proposal, message.from());
if (response == null)
MessagingService.instance().respondWithFailure(UNKNOWN, message);
else
MessagingService.instance().respond(response, message);
}
public static Response execute(Proposal proposal, InetAddressAndPort from)
{
if (!Paxos.isInRangeAndShouldProcess(from, proposal.update.partitionKey(), proposal.update.metadata(), false))
return null;
long start = nanoTime();
try (PaxosState state = PaxosState.get(proposal))
{
return new Response(state.acceptIfLatest(proposal));
}
finally
{
Keyspace.openAndGetStore(proposal.update.metadata()).metric.casPropose.addNano(nanoTime() - start);
}
}
}
public static class RequestSerializer implements IVersionedSerializer
{
@Override
public void serialize(Request request, DataOutputPlus out, int version) throws IOException
{
Proposal.serializer.serialize(request.proposal, out, version);
}
@Override
public Request deserialize(DataInputPlus in, int version) throws IOException
{
Proposal propose = Proposal.serializer.deserialize(in, version);
return new Request(propose);
}
@Override
public long serializedSize(Request request, int version)
{
return Proposal.serializer.serializedSize(request.proposal, version);
}
}
public static class ResponseSerializer implements IVersionedSerializer
{
public void serialize(Response response, DataOutputPlus out, int version) throws IOException
{
out.writeBoolean(response.supersededBy != null);
if (response.supersededBy != null)
response.supersededBy.serialize(out);
}
public Response deserialize(DataInputPlus in, int version) throws IOException
{
boolean isSuperseded = in.readBoolean();
return isSuperseded ? new Response(Ballot.deserialize(in)) : new Response(null);
}
public long serializedSize(Response response, int version)
{
return response.supersededBy != null
? TypeSizes.sizeof(true) + Ballot.sizeInBytes()
: TypeSizes.sizeof(false);
}
}
}
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