[GitHub] [cassandra] maedhroz commented on a change in pull request #493: CASSANDRA-8272 trunk Fix replica-side filtering

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maedhroz commented on a change in pull request #493:
URL: https://github.com/apache/cassandra/pull/493#discussion_r428293783



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File path: src/java/org/apache/cassandra/service/reads/ReplicaFilteringProtection.java
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@@ -0,0 +1,473 @@
+/*
+ * 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;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.NavigableSet;
+import java.util.SortedMap;
+import java.util.TreeMap;
+import java.util.stream.Collectors;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.cassandra.concurrent.Stage;
+import org.apache.cassandra.db.Clustering;
+import org.apache.cassandra.db.ColumnFamilyStore;
+import org.apache.cassandra.db.Columns;
+import org.apache.cassandra.db.ConsistencyLevel;
+import org.apache.cassandra.db.DecoratedKey;
+import org.apache.cassandra.db.DeletionTime;
+import org.apache.cassandra.db.Keyspace;
+import org.apache.cassandra.db.ReadCommand;
+import org.apache.cassandra.db.RegularAndStaticColumns;
+import org.apache.cassandra.db.SinglePartitionReadCommand;
+import org.apache.cassandra.db.filter.ClusteringIndexFilter;
+import org.apache.cassandra.db.filter.ClusteringIndexNamesFilter;
+import org.apache.cassandra.db.partitions.UnfilteredPartitionIterator;
+import org.apache.cassandra.db.partitions.UnfilteredPartitionIterators;
+import org.apache.cassandra.db.rows.EncodingStats;
+import org.apache.cassandra.db.rows.RangeTombstoneMarker;
+import org.apache.cassandra.db.rows.Row;
+import org.apache.cassandra.db.rows.Rows;
+import org.apache.cassandra.db.rows.Unfiltered;
+import org.apache.cassandra.db.rows.UnfilteredRowIterator;
+import org.apache.cassandra.db.rows.UnfilteredRowIterators;
+import org.apache.cassandra.exceptions.ReadTimeoutException;
+import org.apache.cassandra.exceptions.UnavailableException;
+import org.apache.cassandra.locator.Endpoints;
+import org.apache.cassandra.locator.Replica;
+import org.apache.cassandra.locator.ReplicaPlan;
+import org.apache.cassandra.locator.ReplicaPlans;
+import org.apache.cassandra.metrics.TableMetrics;
+import org.apache.cassandra.net.MessagingService;
+import org.apache.cassandra.schema.TableMetadata;
+import org.apache.cassandra.service.StorageProxy;
+import org.apache.cassandra.service.reads.repair.NoopReadRepair;
+import org.apache.cassandra.tracing.Tracing;
+import org.apache.cassandra.utils.btree.BTreeSet;
+
+/**
+ * Helper in charge of collecting additional queries to be done on the coordinator to protect against invalid results
+ * being included due to replica-side filtering (secondary indexes or {@code ALLOW * FILTERING}).
+ * <p>
+ * When using replica-side filtering with CL>ONE, a replica can send a stale result satisfying the filter, while updated
+ * replicas won't send a corresponding tombstone to discard that result during reconciliation. This helper identifies
+ * the rows in a replica response that don't have a corresponding row in other replica responses, and requests them by
+ * primary key to the "silent" replicas in a second fetch round.
+ * <p>
+ * See CASSANDRA-8272 and CASSANDRA-8273 for further details.
+ */
+class ReplicaFilteringProtection<E extends Endpoints<E>>

Review comment:
       @jasonstack Is your worry just that we'll issue useless RFP requests to transient replicas that have already removed their versions of the relevant rows via incremental repair? Is that actually a correctness concern?
   
   It seems like we should be able to ignore transient replicas most of the time anyway as long as we have enough full replicas to meet the original query's read CL...




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