Github user shixiaogang commented on a diff in the pull request:
https://github.com/apache/flink/pull/3336#discussion_r102126863
--- Diff:
flink-contrib/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBMapState.java
---
@@ -0,0 +1,579 @@
+/*
+ * 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
+ * <p/>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p/>
+ * 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.state.MapState;
+import org.apache.flink.api.common.state.MapStateDescriptor;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.apache.flink.api.java.tuple.Tuple3;
+import org.apache.flink.api.java.tuple.Tuple4;
+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.query.netty.message.KvStateRequestSerializer;
+import org.apache.flink.runtime.state.KeyGroupRangeAssignment;
+import org.apache.flink.runtime.state.internal.InternalMapState;
+import org.apache.flink.util.Preconditions;
+import org.rocksdb.ColumnFamilyHandle;
+import org.rocksdb.RocksDB;
+import org.rocksdb.RocksDBException;
+import org.rocksdb.RocksIterator;
+import org.rocksdb.WriteOptions;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.Map;
+
+/**
+ * {@link MapState} implementation that stores state in RocksDB.
+ * <p>
+ * <p>{@link RocksDBStateBackend} must ensure that we set the
+ * {@link org.rocksdb.StringAppendOperator} on the column family that we
use for our state since
+ * we use the {@code merge()} call.
+ *
+ * @param <K> The type of the key.
+ * @param <N> The type of the namespace.
+ * @param <UK> The type of the keys in the map state.
+ * @param <UV> The type of the values in the map state.
+ */
+public class RocksDBMapState<K, N, UK, UV>
+ extends AbstractRocksDBState<K, N, MapState<UK, UV>,
MapStateDescriptor<UK, UV>, Map<UK, UV>>
+ implements InternalMapState<N, UK, UV> {
+
+ /** Serializer for the keys and values */
+ private final TypeSerializer<UK> userKeySerializer;
+ private final TypeSerializer<UV> userValueSerializer;
+
+ /**
+ * We disable writes to the write-ahead-log here. We can't have these
in the base class
+ * because JNI segfaults for some reason if they are.
+ */
+ private final WriteOptions writeOptions;
+
+ /**
+ * Creates a new {@code RocksDBMapState}.
+ *
+ * @param namespaceSerializer The serializer for the namespace.
+ * @param stateDesc The state identifier for the state.
+ */
+ public RocksDBMapState(ColumnFamilyHandle columnFamily,
+ TypeSerializer<N> namespaceSerializer,
+ MapStateDescriptor<UK, UV> stateDesc,
+ RocksDBKeyedStateBackend<K> backend) {
+
+ super(columnFamily, namespaceSerializer, stateDesc, backend);
+
+ this.userKeySerializer = stateDesc.getKeySerializer();
+ this.userValueSerializer = stateDesc.getValueSerializer();
+
+ writeOptions = new WriteOptions();
+ writeOptions.setDisableWAL(true);
+ }
+
+ //
------------------------------------------------------------------------
+ // MapState Implementation
+ //
------------------------------------------------------------------------
+
+ @Override
+ public UV get(UK userKey) throws IOException {
+ try {
+ byte[] rawKeyBytes =
serializeUserKeyWithCurrentKeyAndNamespace(userKey);
+ byte[] rawValueBytes = backend.db.get(columnFamily,
rawKeyBytes);
+
+ return (rawValueBytes == null ? null :
deserializeUserValue(rawValueBytes));
+ } catch (RocksDBException e) {
+ throw new RuntimeException("Error while getting data
from RocksDB.", e);
+ }
+ }
+
+ @Override
+ public void put(UK userKey, UV userValue) throws IOException {
+ if (userValue == null) {
+ remove(userKey);
--- End diff --
I remove those mappings whose values from RocksDB because currently we have
no method to serialize the null value. Many type serializers do not support the
serialization of `null` (e.g. IntSerializer). It also follows
`RocksDBValueState` which removes the data when the value is updated to `null`.
In current implementation, the `get(UK)` method can still get the correct
result if we remove the mapping from RocksDB because we always return `null`
when the key is found in the RocksDB. The only concern is that the result
returned by `contains(UK)` and `size()` will be different from a Map which
supports `null` values.
Actually, I prefer not to remove the entry if its value is `null`. But at
prior to that, I think a different pull request is urgently needed to let all
type serializers support `null` values.
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