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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.schema;
import java.time.Duration;
import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import java.util.Set;
import java.util.UUID;
import java.util.function.BiConsumer;
import java.util.stream.Collectors;
import com.google.common.annotations.VisibleForTesting;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.concurrent.ScheduledExecutors;
import org.apache.cassandra.concurrent.Stage;
import org.apache.cassandra.config.CassandraRelevantProperties;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.Mutation;
import org.apache.cassandra.gms.ApplicationState;
import org.apache.cassandra.gms.EndpointState;
import org.apache.cassandra.gms.Gossiper;
import org.apache.cassandra.gms.IEndpointStateChangeSubscriber;
import org.apache.cassandra.gms.VersionedValue;
import org.apache.cassandra.locator.InetAddressAndPort;
import org.apache.cassandra.net.MessagingService;
import org.apache.cassandra.schema.SchemaTransformation.SchemaTransformationResult;
import org.apache.cassandra.service.StorageService;
import org.apache.cassandra.utils.FBUtilities;
import org.apache.cassandra.utils.Pair;
import org.apache.cassandra.utils.concurrent.AsyncPromise;
import org.apache.cassandra.utils.concurrent.Awaitable;
import static org.apache.cassandra.schema.MigrationCoordinator.MAX_OUTSTANDING_VERSION_REQUESTS;
public class DefaultSchemaUpdateHandler implements SchemaUpdateHandler, IEndpointStateChangeSubscriber
{
private static final Logger logger = LoggerFactory.getLogger(DefaultSchemaUpdateHandler.class);
@VisibleForTesting
final MigrationCoordinator migrationCoordinator;
private final boolean requireSchemas;
private final BiConsumer updateCallback;
private volatile DistributedSchema schema = DistributedSchema.EMPTY;
private volatile AsyncPromise requestedReset;
private MigrationCoordinator createMigrationCoordinator(MessagingService messagingService)
{
return new MigrationCoordinator(messagingService,
Stage.MIGRATION.executor(),
ScheduledExecutors.scheduledTasks,
MAX_OUTSTANDING_VERSION_REQUESTS,
Gossiper.instance,
this::getSchemaVersionForCoordinator,
this::applyMutationsFromCoordinator);
}
public DefaultSchemaUpdateHandler(BiConsumer updateCallback)
{
this(null, MessagingService.instance(), !CassandraRelevantProperties.BOOTSTRAP_SKIP_SCHEMA_CHECK.getBoolean(), updateCallback);
}
public DefaultSchemaUpdateHandler(MigrationCoordinator migrationCoordinator,
MessagingService messagingService,
boolean requireSchemas,
BiConsumer updateCallback)
{
this.requireSchemas = requireSchemas;
this.updateCallback = updateCallback;
this.migrationCoordinator = migrationCoordinator == null ? createMigrationCoordinator(messagingService) : migrationCoordinator;
Gossiper.instance.register(this);
SchemaPushVerbHandler.instance.register(msg -> {
synchronized (this)
{
if (requestedReset == null)
applyMutations(msg.payload);
}
});
SchemaPullVerbHandler.instance.register(msg -> {
try
{
messagingService.send(msg.responseWith(getSchemaMutations()), msg.from());
}
catch (RuntimeException ex)
{
logger.error("Failed to send schema mutations to " + msg.from(), ex);
}
});
}
public synchronized void start()
{
if (StorageService.instance.isReplacing())
onRemove(DatabaseDescriptor.getReplaceAddress());
SchemaKeyspace.saveSystemKeyspacesSchema();
migrationCoordinator.start();
}
@Override
public boolean waitUntilReady(Duration timeout)
{
logger.debug("Waiting for schema to be ready (max {})", timeout);
boolean schemasReceived = migrationCoordinator.awaitSchemaRequests(timeout.toMillis());
if (schemasReceived)
return true;
logger.warn("There are nodes in the cluster with a different schema version than us, from which we did not merge schemas: " +
"our version: ({}), outstanding versions -> endpoints: {}. Use -D{}=true to ignore this, " +
"-D{}= to skip specific endpoints, or -D{}= to skip specific schema versions",
Schema.instance.getVersion(),
migrationCoordinator.outstandingVersions(),
CassandraRelevantProperties.BOOTSTRAP_SKIP_SCHEMA_CHECK.getKey(),
CassandraRelevantProperties.IGNORED_SCHEMA_CHECK_ENDPOINTS.getKey(),
CassandraRelevantProperties.IGNORED_SCHEMA_CHECK_VERSIONS.getKey());
if (requireSchemas)
{
logger.error("Didn't receive schemas for all known versions within the {}. Use -D{}=true to skip this check.",
timeout, CassandraRelevantProperties.BOOTSTRAP_SKIP_SCHEMA_CHECK.getKey());
return false;
}
return true;
}
@Override
public void onRemove(InetAddressAndPort endpoint)
{
migrationCoordinator.removeAndIgnoreEndpoint(endpoint);
}
@Override
public void onChange(InetAddressAndPort endpoint, ApplicationState state, VersionedValue value)
{
if (state == ApplicationState.SCHEMA)
{
EndpointState epState = Gossiper.instance.getEndpointStateForEndpoint(endpoint);
if (epState != null && !Gossiper.instance.isDeadState(epState) && StorageService.instance.getTokenMetadata().isMember(endpoint))
{
migrationCoordinator.reportEndpointVersion(endpoint, UUID.fromString(value.value));
}
}
}
@Override
public void onJoin(InetAddressAndPort endpoint, EndpointState epState)
{
// no-op
}
@Override
public void beforeChange(InetAddressAndPort endpoint, EndpointState currentState, ApplicationState newStateKey, VersionedValue newValue)
{
// no-op
}
@Override
public void onAlive(InetAddressAndPort endpoint, EndpointState state)
{
// no-op
}
@Override
public void onDead(InetAddressAndPort endpoint, EndpointState state)
{
// no-op
}
@Override
public void onRestart(InetAddressAndPort endpoint, EndpointState state)
{
// no-op
}
private synchronized SchemaTransformationResult applyMutations(Collection schemaMutations)
{
// fetch the current state of schema for the affected keyspaces only
DistributedSchema before = schema;
// apply the schema mutations
SchemaKeyspace.applyChanges(schemaMutations);
// only compare the keyspaces affected by this set of schema mutations
Set affectedKeyspaces = SchemaKeyspace.affectedKeyspaces(schemaMutations);
// apply the schema mutations and fetch the new versions of the altered keyspaces
Keyspaces updatedKeyspaces = SchemaKeyspace.fetchKeyspaces(affectedKeyspaces);
Set removedKeyspaces = affectedKeyspaces.stream().filter(ks -> !updatedKeyspaces.containsKeyspace(ks)).collect(Collectors.toSet());
Keyspaces afterKeyspaces = before.getKeyspaces().withAddedOrReplaced(updatedKeyspaces).without(removedKeyspaces);
Keyspaces.KeyspacesDiff diff = Keyspaces.diff(before.getKeyspaces(), afterKeyspaces);
UUID version = SchemaKeyspace.calculateSchemaDigest();
DistributedSchema after = new DistributedSchema(afterKeyspaces, version);
SchemaTransformationResult update = new SchemaTransformationResult(before, after, diff);
logger.info("Applying schema change due to received mutations: {}", update);
updateSchema(update, false);
return update;
}
@Override
public synchronized SchemaTransformationResult apply(SchemaTransformation transformation, boolean local)
{
DistributedSchema before = schema;
Keyspaces afterKeyspaces = transformation.apply(before.getKeyspaces());
Keyspaces.KeyspacesDiff diff = Keyspaces.diff(before.getKeyspaces(), afterKeyspaces);
if (diff.isEmpty())
return new SchemaTransformationResult(before, before, diff);
Collection mutations = SchemaKeyspace.convertSchemaDiffToMutations(diff, transformation.fixedTimestampMicros().orElse(FBUtilities.timestampMicros()));
SchemaKeyspace.applyChanges(mutations);
DistributedSchema after = new DistributedSchema(afterKeyspaces, SchemaKeyspace.calculateSchemaDigest());
SchemaTransformationResult update = new SchemaTransformationResult(before, after, diff);
updateSchema(update, local);
if (!local)
{
migrationCoordinator.executor.submit(() -> {
Pair, Set> endpoints = migrationCoordinator.pushSchemaMutations(mutations);
SchemaAnnouncementDiagnostics.schemaTransformationAnnounced(endpoints.left(), endpoints.right(), transformation);
});
}
return update;
}
private void updateSchema(SchemaTransformationResult update, boolean local)
{
if (!update.diff.isEmpty())
{
this.schema = update.after;
logger.debug("Schema updated: {}", update);
updateCallback.accept(update, true);
if (!local)
{
migrationCoordinator.announce(update.after.getVersion());
}
}
else
{
logger.debug("Schema update is empty - skipping");
}
}
private synchronized void reload()
{
DistributedSchema before = this.schema;
DistributedSchema after = new DistributedSchema(SchemaKeyspace.fetchNonSystemKeyspaces(), SchemaKeyspace.calculateSchemaDigest());
Keyspaces.KeyspacesDiff diff = Keyspaces.diff(before.getKeyspaces(), after.getKeyspaces());
SchemaTransformationResult update = new SchemaTransformationResult(before, after, diff);
updateSchema(update, false);
}
@Override
public void reset(boolean local)
{
if (local)
{
reload();
}
else
{
migrationCoordinator.reset();
if (!migrationCoordinator.awaitSchemaRequests(CassandraRelevantProperties.MIGRATION_DELAY.getLong()))
{
logger.error("Timeout exceeded when waiting for schema from other nodes");
}
}
}
/**
* When clear is called the update handler will flag that the clear was requested. It means that migration
* coordinator will think that we have empty schema version and will apply whatever it receives from other nodes.
* When a first attempt to apply mutations from other node is called, it will first clear the schema and apply
* the mutations on a truncated table. The flag is then reset.
*
* This way the clear is postponed until we really fetch any schema we can use as a replacement. Otherwise, nothing
* will happen. We will simply reset the flag after the timeout and throw exceptions to the caller.
*
* @return
*/
@Override
public Awaitable clear()
{
synchronized (this)
{
if (requestedReset == null)
{
requestedReset = new AsyncPromise<>();
migrationCoordinator.reset();
}
return requestedReset;
}
}
private UUID getSchemaVersionForCoordinator()
{
if (requestedReset != null)
return SchemaConstants.emptyVersion;
else
return schema.getVersion();
}
private synchronized void applyMutationsFromCoordinator(InetAddressAndPort from, Collection mutations)
{
if (requestedReset != null && !mutations.isEmpty())
{
schema = DistributedSchema.EMPTY;
SchemaKeyspace.truncate();
requestedReset.setSuccess(null);
requestedReset = null;
}
applyMutations(mutations);
}
private synchronized Collection getSchemaMutations()
{
if (requestedReset != null)
return Collections.emptyList();
else
return SchemaKeyspace.convertSchemaToMutations();
}
public Map> getOutstandingSchemaVersions()
{
return migrationCoordinator.outstandingVersions();
}
}
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