Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/6228#discussion_r199442186
--- Diff: flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBOrderedStore.java
---
@@ -0,0 +1,283 @@
+/*
+ * 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 RocksDBOrderedStore<T> implements CachingInternalPriorityQueueSet.OrderedSetStore<T>
{
+
+ /** Serialized empty value to insert into RocksDB. */
+ private static final byte[] DUMMY_BYTES = "0".getBytes(ConfigConstants.DEFAULT_CHARSET);
+
+ /** The RocksDB instance that serves as store. */
+ @Nonnull
+ private final RocksDB db;
+
+ /** Handle to the column family of the RocksDB instance in which the elements are stored.
*/
+ @Nonnull
+ private final ColumnFamilyHandle columnFamilyHandle;
+
+ /** Read options for RocksDB. */
+ @Nonnull
+ private final ReadOptions readOptions;
+
+ /**
+ * Serializer for the contained elements. The lexicographical order of the bytes of
serialized objects must be
+ * aligned with their logical order.
+ */
+ @Nonnull
+ private final TypeSerializer<T> byteOrderProducingSerializer;
+
+ /** Wrapper to batch all writes to RocksDB. */
+ @Nonnull
+ private final RocksDBWriteBatchWrapper batchWrapper;
+
+ /** The key-group id of all elements stored in this instance. */
+ @Nonnegative
+ private final int keyGroupId;
+
+ /** The key-group id in serialized form. */
+ @Nonnull
+ private final byte[] groupPrefixBytes;
+
+ /** Output stream that helps to serialize elements. */
+ @Nonnull
+ private final ByteArrayOutputStreamWithPos outputStream;
+
+ /** Output view that helps to serialize elements, must wrap the output stream. */
+ @Nonnull
+ private final DataOutputViewStreamWrapper outputView;
+
+ public RocksDBOrderedStore(
+ @Nonnegative int keyGroupId,
+ @Nonnull RocksDB db,
+ @Nonnull ColumnFamilyHandle columnFamilyHandle,
+ @Nonnull ReadOptions readOptions,
+ @Nonnull TypeSerializer<T> byteOrderProducingSerializer,
+ @Nonnull ByteArrayOutputStreamWithPos outputStream,
+ @Nonnull DataOutputViewStreamWrapper outputView,
+ @Nonnull RocksDBWriteBatchWrapper batchWrapper) {
+ this.db = db;
+ this.columnFamilyHandle = columnFamilyHandle;
+ this.readOptions = readOptions;
+ this.byteOrderProducingSerializer = byteOrderProducingSerializer;
+ this.outputStream = outputStream;
+ this.outputView = outputView;
+ this.keyGroupId = keyGroupId;
+ this.batchWrapper = batchWrapper;
+ this.groupPrefixBytes = createKeyGroupBytes(keyGroupId);
+ }
+
+ private byte[] createKeyGroupBytes(int keyGroupId) {
--- End diff --
I did it for simplicity, but you are right. Will change it to variable size.
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