adelapena commented on code in PR #2673: URL: https://github.com/apache/cassandra/pull/2673#discussion_r1356710478
########## src/java/org/apache/cassandra/service/reads/range/ScanAllRangesCommandIterator.java: ########## @@ -0,0 +1,108 @@ +/* + * 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.reads.range; + +import java.util.HashSet; +import java.util.Set; + +import com.google.common.base.Preconditions; + +import org.apache.cassandra.db.ConsistencyLevel; +import org.apache.cassandra.db.EmptyIterators; +import org.apache.cassandra.db.Keyspace; +import org.apache.cassandra.db.PartitionRangeReadCommand; +import org.apache.cassandra.db.ReadCommand; +import org.apache.cassandra.db.partitions.PartitionIterator; +import org.apache.cassandra.index.Index; +import org.apache.cassandra.locator.EndpointsForRange; +import org.apache.cassandra.locator.InetAddressAndPort; +import org.apache.cassandra.locator.ReplicaPlan; +import org.apache.cassandra.locator.ReplicaPlans; +import org.apache.cassandra.net.Message; +import org.apache.cassandra.net.MessagingService; +import org.apache.cassandra.service.reads.DataResolver; +import org.apache.cassandra.service.reads.ReadCallback; +import org.apache.cassandra.service.reads.repair.NoopReadRepair; +import org.apache.cassandra.tracing.Tracing; +import org.apache.cassandra.utils.CloseableIterator; + +/** + * A custom {@link RangeCommandIterator} that queries all replicas required by consistency level at once with data range + * specify in {@link PartitionRangeReadCommand}. + * + * This is to speed up {@link Index.QueryPlan#isTopK()} queries that needs to find global top-k rows in the cluster, because + * existing {@link RangeCommandIterator} has to execute a top-k search per vnode range which is wasting resources. + */ +public class ScanAllRangesCommandIterator extends RangeCommandIterator Review Comment: We could also add a line saying that `ScanAllRangesCommandIterator` can only be used with CL=ONE/LOCAL_ONE. I understand we won't be able to use this optimization when we add support for higher CLs, making top-k queries quite expensive for vnodes. At least, not without further changes in `DataResolver`, RFP, RR, etc. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
