Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/6228#discussion_r199816118
--- Diff:
flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBOrderedSetStore.java
---
@@ -0,0 +1,279 @@
+/*
+ * 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.flink.contrib.streaming.state;
+
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.configuration.ConfigConstants;
+import org.apache.flink.core.memory.ByteArrayInputStreamWithPos;
+import org.apache.flink.core.memory.ByteArrayOutputStreamWithPos;
+import org.apache.flink.core.memory.DataInputViewStreamWrapper;
+import org.apache.flink.core.memory.DataOutputViewStreamWrapper;
+import org.apache.flink.runtime.state.heap.CachingInternalPriorityQueueSet;
+import org.apache.flink.util.CloseableIterator;
+import org.apache.flink.util.FlinkRuntimeException;
+
+import org.rocksdb.ColumnFamilyHandle;
+import org.rocksdb.ReadOptions;
+import org.rocksdb.RocksDB;
+import org.rocksdb.RocksDBException;
+
+import javax.annotation.Nonnegative;
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+import java.io.IOException;
+import java.util.NoSuchElementException;
+
+/**
+ * Implementation of {@link
org.apache.flink.runtime.state.heap.CachingInternalPriorityQueueSet.OrderedSetStore}
+ * based on RocksDB.
+ *
+ * <p>IMPORTANT: The store is ordered and the order is determined by the
lexicographic order of the byte sequences
+ * produced by the provided serializer for the elements!
+ *
+ * @param <T> the type of stored elements.
+ */
+public class RocksDBOrderedSetStore<T> implements
CachingInternalPriorityQueueSet.OrderedSetStore<T> {
+
+ /** Serialized empty value to insert into RocksDB. */
+ private static final byte[] DUMMY_BYTES =
"0".getBytes(ConfigConstants.DEFAULT_CHARSET);
--- End diff --
ð
---
