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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.batchlog;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.Collections2;
import com.google.common.collect.Iterables;
import com.google.common.util.concurrent.RateLimiter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.concurrent.DebuggableScheduledThreadPoolExecutor;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.cql3.UntypedResultSet;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.ConsistencyLevel;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.db.Mutation;
import org.apache.cassandra.db.SystemKeyspace;
import org.apache.cassandra.db.WriteType;
import org.apache.cassandra.db.marshal.BytesType;
import org.apache.cassandra.db.marshal.UUIDType;
import org.apache.cassandra.db.partitions.PartitionUpdate;
import org.apache.cassandra.dht.Token;
import org.apache.cassandra.exceptions.WriteFailureException;
import org.apache.cassandra.exceptions.WriteTimeoutException;
import org.apache.cassandra.gms.FailureDetector;
import org.apache.cassandra.hints.Hint;
import org.apache.cassandra.hints.HintsService;
import org.apache.cassandra.io.util.DataInputBuffer;
import org.apache.cassandra.io.util.DataOutputBuffer;
import org.apache.cassandra.locator.InetAddressAndPort;
import org.apache.cassandra.locator.Replica;
import org.apache.cassandra.locator.ReplicaLayout;
import org.apache.cassandra.locator.ReplicaPlan;
import org.apache.cassandra.locator.Replicas;
import org.apache.cassandra.net.Message;
import org.apache.cassandra.net.MessageFlag;
import org.apache.cassandra.net.MessagingService;
import org.apache.cassandra.schema.SchemaConstants;
import org.apache.cassandra.schema.TableId;
import org.apache.cassandra.service.StorageService;
import org.apache.cassandra.service.WriteResponseHandler;
import org.apache.cassandra.utils.ExecutorUtils;
import org.apache.cassandra.utils.FBUtilities;
import org.apache.cassandra.utils.MBeanWrapper;
import org.apache.cassandra.utils.UUIDGen;
import static com.google.common.collect.Iterables.transform;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static org.apache.cassandra.cql3.QueryProcessor.executeInternal;
import static org.apache.cassandra.cql3.QueryProcessor.executeInternalWithPaging;
import static org.apache.cassandra.net.Verb.MUTATION_REQ;
public class BatchlogManager implements BatchlogManagerMBean
{
public static final String MBEAN_NAME = "org.apache.cassandra.db:type=BatchlogManager";
private static final long REPLAY_INTERVAL = 10 * 1000; // milliseconds
static final int DEFAULT_PAGE_SIZE = 128;
private static final Logger logger = LoggerFactory.getLogger(BatchlogManager.class);
public static final BatchlogManager instance = new BatchlogManager();
public static final long BATCHLOG_REPLAY_TIMEOUT = Long.getLong("cassandra.batchlog.replay_timeout_in_ms", DatabaseDescriptor.getWriteRpcTimeout(MILLISECONDS) * 2);
private volatile long totalBatchesReplayed = 0; // no concurrency protection necessary as only written by replay thread.
private volatile UUID lastReplayedUuid = UUIDGen.minTimeUUID(0);
// Single-thread executor service for scheduling and serializing log replay.
private final ScheduledExecutorService batchlogTasks;
private final RateLimiter rateLimiter = RateLimiter.create(Double.MAX_VALUE);
public BatchlogManager()
{
ScheduledThreadPoolExecutor executor = new DebuggableScheduledThreadPoolExecutor("BatchlogTasks");
executor.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
batchlogTasks = executor;
}
public void start()
{
MBeanWrapper.instance.registerMBean(this, MBEAN_NAME);
batchlogTasks.scheduleWithFixedDelay(this::replayFailedBatches,
StorageService.RING_DELAY,
REPLAY_INTERVAL,
MILLISECONDS);
}
public void shutdownAndWait(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException
{
ExecutorUtils.shutdownAndWait(timeout, unit, batchlogTasks);
}
public static void remove(UUID id)
{
new Mutation(PartitionUpdate.fullPartitionDelete(SystemKeyspace.Batches,
UUIDType.instance.decompose(id),
FBUtilities.timestampMicros(),
FBUtilities.nowInSeconds()))
.apply();
}
public static void store(Batch batch)
{
store(batch, true);
}
public static void store(Batch batch, boolean durableWrites)
{
List mutations = new ArrayList<>(batch.encodedMutations.size() + batch.decodedMutations.size());
mutations.addAll(batch.encodedMutations);
for (Mutation mutation : batch.decodedMutations)
{
try (DataOutputBuffer buffer = new DataOutputBuffer())
{
Mutation.serializer.serialize(mutation, buffer, MessagingService.current_version);
mutations.add(buffer.buffer());
}
catch (IOException e)
{
// shouldn't happen
throw new AssertionError(e);
}
}
PartitionUpdate.SimpleBuilder builder = PartitionUpdate.simpleBuilder(SystemKeyspace.Batches, batch.id);
builder.row()
.timestamp(batch.creationTime)
.add("version", MessagingService.current_version)
.appendAll("mutations", mutations);
builder.buildAsMutation().apply(durableWrites);
}
@VisibleForTesting
public int countAllBatches()
{
String query = String.format("SELECT count(*) FROM %s.%s", SchemaConstants.SYSTEM_KEYSPACE_NAME, SystemKeyspace.BATCHES);
UntypedResultSet results = executeInternal(query);
if (results == null || results.isEmpty())
return 0;
return (int) results.one().getLong("count");
}
public long getTotalBatchesReplayed()
{
return totalBatchesReplayed;
}
public void forceBatchlogReplay() throws Exception
{
startBatchlogReplay().get();
}
public Future startBatchlogReplay()
{
// If a replay is already in progress this request will be executed after it completes.
return batchlogTasks.submit(this::replayFailedBatches);
}
void performInitialReplay() throws InterruptedException, ExecutionException
{
// Invokes initial replay. Used for testing only.
batchlogTasks.submit(this::replayFailedBatches).get();
}
private void replayFailedBatches()
{
logger.trace("Started replayFailedBatches");
// rate limit is in bytes per second. Uses Double.MAX_VALUE if disabled (set to 0 in cassandra.yaml).
// max rate is scaled by the number of nodes in the cluster (same as for HHOM - see CASSANDRA-5272).
int endpointsCount = StorageService.instance.getTokenMetadata().getSizeOfAllEndpoints();
if (endpointsCount <= 0)
{
logger.trace("Replay cancelled as there are no peers in the ring.");
return;
}
setRate(DatabaseDescriptor.getBatchlogReplayThrottleInKB());
UUID limitUuid = UUIDGen.maxTimeUUID(System.currentTimeMillis() - getBatchlogTimeout());
ColumnFamilyStore store = Keyspace.open(SchemaConstants.SYSTEM_KEYSPACE_NAME).getColumnFamilyStore(SystemKeyspace.BATCHES);
int pageSize = calculatePageSize(store);
// There cannot be any live content where token(id) <= token(lastReplayedUuid) as every processed batch is
// deleted, but the tombstoned content may still be present in the tables. To avoid walking over it we specify
// token(id) > token(lastReplayedUuid) as part of the query.
String query = String.format("SELECT id, mutations, version FROM %s.%s WHERE token(id) > token(?) AND token(id) <= token(?)",
SchemaConstants.SYSTEM_KEYSPACE_NAME,
SystemKeyspace.BATCHES);
UntypedResultSet batches = executeInternalWithPaging(query, pageSize, lastReplayedUuid, limitUuid);
processBatchlogEntries(batches, pageSize, rateLimiter);
lastReplayedUuid = limitUuid;
logger.trace("Finished replayFailedBatches");
}
/**
* Sets the rate for the current rate limiter. When {@code throttleInKB} is 0, this sets the rate to
* {@link Double#MAX_VALUE} bytes per second.
*
* @param throttleInKB throughput to set in KB per second
*/
public void setRate(final int throttleInKB)
{
int endpointsCount = StorageService.instance.getTokenMetadata().getSizeOfAllEndpoints();
if (endpointsCount > 0)
{
int endpointThrottleInKB = throttleInKB / endpointsCount;
double throughput = endpointThrottleInKB == 0 ? Double.MAX_VALUE : endpointThrottleInKB * 1024.0;
if (rateLimiter.getRate() != throughput)
{
logger.debug("Updating batchlog replay throttle to {} KB/s, {} KB/s per endpoint", throttleInKB, endpointThrottleInKB);
rateLimiter.setRate(throughput);
}
}
}
// read less rows (batches) per page if they are very large
static int calculatePageSize(ColumnFamilyStore store)
{
double averageRowSize = store.getMeanPartitionSize();
if (averageRowSize <= 0)
return DEFAULT_PAGE_SIZE;
return (int) Math.max(1, Math.min(DEFAULT_PAGE_SIZE, 4 * 1024 * 1024 / averageRowSize));
}
private void processBatchlogEntries(UntypedResultSet batches, int pageSize, RateLimiter rateLimiter)
{
int positionInPage = 0;
ArrayList unfinishedBatches = new ArrayList<>(pageSize);
Set hintedNodes = new HashSet<>();
Set replayedBatches = new HashSet<>();
Exception caughtException = null;
int skipped = 0;
// Sending out batches for replay without waiting for them, so that one stuck batch doesn't affect others
for (UntypedResultSet.Row row : batches)
{
UUID id = row.getUUID("id");
int version = row.getInt("version");
try
{
ReplayingBatch batch = new ReplayingBatch(id, version, row.getList("mutations", BytesType.instance));
if (batch.replay(rateLimiter, hintedNodes) > 0)
{
unfinishedBatches.add(batch);
}
else
{
remove(id); // no write mutations were sent (either expired or all CFs involved truncated).
++totalBatchesReplayed;
}
}
catch (IOException e)
{
logger.warn("Skipped batch replay of {} due to {}", id, e.getMessage());
caughtException = e;
remove(id);
++skipped;
}
if (++positionInPage == pageSize)
{
// We have reached the end of a batch. To avoid keeping more than a page of mutations in memory,
// finish processing the page before requesting the next row.
finishAndClearBatches(unfinishedBatches, hintedNodes, replayedBatches);
positionInPage = 0;
}
}
finishAndClearBatches(unfinishedBatches, hintedNodes, replayedBatches);
if (caughtException != null)
logger.warn(String.format("Encountered %d unexpected exceptions while sending out batches", skipped), caughtException);
// to preserve batch guarantees, we must ensure that hints (if any) have made it to disk, before deleting the batches
HintsService.instance.flushAndFsyncBlockingly(transform(hintedNodes, StorageService.instance::getHostIdForEndpoint));
// once all generated hints are fsynced, actually delete the batches
replayedBatches.forEach(BatchlogManager::remove);
}
private void finishAndClearBatches(ArrayList batches, Set hintedNodes, Set replayedBatches)
{
// schedule hints for timed out deliveries
for (ReplayingBatch batch : batches)
{
batch.finish(hintedNodes);
replayedBatches.add(batch.id);
}
totalBatchesReplayed += batches.size();
batches.clear();
}
public static long getBatchlogTimeout()
{
return BATCHLOG_REPLAY_TIMEOUT; // enough time for the actual write + BM removal mutation
}
private static class ReplayingBatch
{
private final UUID id;
private final long writtenAt;
private final List mutations;
private final int replayedBytes;
private List> replayHandlers;
ReplayingBatch(UUID id, int version, List serializedMutations) throws IOException
{
this.id = id;
this.writtenAt = UUIDGen.unixTimestamp(id);
this.mutations = new ArrayList<>(serializedMutations.size());
this.replayedBytes = addMutations(version, serializedMutations);
}
public int replay(RateLimiter rateLimiter, Set hintedNodes) throws IOException
{
logger.trace("Replaying batch {}", id);
if (mutations.isEmpty())
return 0;
int gcgs = gcgs(mutations);
if (MILLISECONDS.toSeconds(writtenAt) + gcgs <= FBUtilities.nowInSeconds())
return 0;
replayHandlers = sendReplays(mutations, writtenAt, hintedNodes);
rateLimiter.acquire(replayedBytes); // acquire afterwards, to not mess up ttl calculation.
return replayHandlers.size();
}
public void finish(Set hintedNodes)
{
for (int i = 0; i < replayHandlers.size(); i++)
{
ReplayWriteResponseHandler handler = replayHandlers.get(i);
try
{
handler.get();
}
catch (WriteTimeoutException|WriteFailureException e)
{
logger.trace("Failed replaying a batched mutation to a node, will write a hint");
logger.trace("Failure was : {}", e.getMessage());
// writing hints for the rest to hints, starting from i
writeHintsForUndeliveredEndpoints(i, hintedNodes);
return;
}
}
}
private int addMutations(int version, List serializedMutations) throws IOException
{
int ret = 0;
for (ByteBuffer serializedMutation : serializedMutations)
{
ret += serializedMutation.remaining();
try (DataInputBuffer in = new DataInputBuffer(serializedMutation, true))
{
addMutation(Mutation.serializer.deserialize(in, version));
}
}
return ret;
}
// Remove CFs that have been truncated since. writtenAt and SystemTable#getTruncatedAt() both return millis.
// We don't abort the replay entirely b/c this can be considered a success (truncated is same as delivered then
// truncated.
private void addMutation(Mutation mutation)
{
for (TableId tableId : mutation.getTableIds())
if (writtenAt <= SystemKeyspace.getTruncatedAt(tableId))
mutation = mutation.without(tableId);
if (!mutation.isEmpty())
mutations.add(mutation);
}
private void writeHintsForUndeliveredEndpoints(int startFrom, Set hintedNodes)
{
int gcgs = gcgs(mutations);
// expired
if (MILLISECONDS.toSeconds(writtenAt) + gcgs <= FBUtilities.nowInSeconds())
return;
for (int i = startFrom; i < replayHandlers.size(); i++)
{
ReplayWriteResponseHandler handler = replayHandlers.get(i);
Mutation undeliveredMutation = mutations.get(i);
if (handler != null)
{
hintedNodes.addAll(handler.undelivered);
HintsService.instance.write(Collections2.transform(handler.undelivered, StorageService.instance::getHostIdForEndpoint),
Hint.create(undeliveredMutation, writtenAt));
}
}
}
private static List> sendReplays(List mutations,
long writtenAt,
Set hintedNodes)
{
List> handlers = new ArrayList<>(mutations.size());
for (Mutation mutation : mutations)
{
ReplayWriteResponseHandler handler = sendSingleReplayMutation(mutation, writtenAt, hintedNodes);
handlers.add(handler);
}
return handlers;
}
/**
* We try to deliver the mutations to the replicas ourselves if they are alive and only resort to writing hints
* when a replica is down or a write request times out.
*
* @return direct delivery handler to wait on
*/
private static ReplayWriteResponseHandler sendSingleReplayMutation(final Mutation mutation,
long writtenAt,
Set hintedNodes)
{
String ks = mutation.getKeyspaceName();
Keyspace keyspace = Keyspace.open(ks);
Token tk = mutation.key().getToken();
// TODO: this logic could do with revisiting at some point, as it is unclear what its rationale is
// we perform a local write, ignoring errors and inline in this thread (potentially slowing replay down)
// effectively bumping CL for locally owned writes and also potentially stalling log replay if an error occurs
// once we decide how it should work, it can also probably be simplified, and avoid constructing a ReplicaPlan directly
ReplicaLayout.ForTokenWrite liveAndDown = ReplicaLayout.forTokenWriteLiveAndDown(keyspace, tk);
Replicas.temporaryAssertFull(liveAndDown.all()); // TODO in CASSANDRA-14549
Replica selfReplica = liveAndDown.all().selfIfPresent();
if (selfReplica != null)
mutation.apply();
ReplicaLayout.ForTokenWrite liveRemoteOnly = liveAndDown.filter(
r -> FailureDetector.isReplicaAlive.test(r) && r != selfReplica);
for (Replica replica : liveAndDown.all())
{
if (replica == selfReplica || liveRemoteOnly.all().contains(replica))
continue;
hintedNodes.add(replica.endpoint());
HintsService.instance.write(StorageService.instance.getHostIdForEndpoint(replica.endpoint()),
Hint.create(mutation, writtenAt));
}
ReplicaPlan.ForTokenWrite replicaPlan = new ReplicaPlan.ForTokenWrite(keyspace, liveAndDown.replicationStrategy(),
ConsistencyLevel.ONE, liveRemoteOnly.pending(), liveRemoteOnly.all(), liveRemoteOnly.all(), liveRemoteOnly.all());
ReplayWriteResponseHandler handler = new ReplayWriteResponseHandler<>(replicaPlan, System.nanoTime());
Message message = Message.outWithFlag(MUTATION_REQ, mutation, MessageFlag.CALL_BACK_ON_FAILURE);
for (Replica replica : liveRemoteOnly.all())
MessagingService.instance().sendWriteWithCallback(message, replica, handler, false);
return handler;
}
private static int gcgs(Collection mutations)
{
int gcgs = Integer.MAX_VALUE;
for (Mutation mutation : mutations)
gcgs = Math.min(gcgs, mutation.smallestGCGS());
return gcgs;
}
/**
* A wrapper of WriteResponseHandler that stores the addresses of the endpoints from
* which we did not receive a successful response.
*/
private static class ReplayWriteResponseHandler extends WriteResponseHandler
{
private final Set undelivered = Collections.newSetFromMap(new ConcurrentHashMap<>());
ReplayWriteResponseHandler(ReplicaPlan.ForTokenWrite replicaPlan, long queryStartNanoTime)
{
super(replicaPlan, null, WriteType.UNLOGGED_BATCH, queryStartNanoTime);
Iterables.addAll(undelivered, replicaPlan.contacts().endpoints());
}
@Override
protected int blockFor()
{
return this.replicaPlan.contacts().size();
}
@Override
public void onResponse(Message m)
{
boolean removed = undelivered.remove(m == null ? FBUtilities.getBroadcastAddressAndPort() : m.from());
assert removed;
super.onResponse(m);
}
}
}
}