[GitHub] [flink] carp84 commented on a change in pull request #9501: [FLINK-12697] [State Backends] Support on-disk state storage for spill-able heap backend

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carp84 commented on a change in pull request #9501: [FLINK-12697] [State Backends] Support on-disk state storage for spill-able heap backend
URL: https://github.com/apache/flink/pull/9501#discussion_r325646539
 
 

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 File path: flink-state-backends/flink-statebackend-heap-spillable/src/main/java/org/apache/flink/runtime/state/heap/CopyOnWriteSkipListStateMapSnapshot.java
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+/*
+ * 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.runtime.state.heap;
+
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.apache.flink.core.memory.DataOutputView;
+import org.apache.flink.runtime.state.StateSnapshotTransformer;
+import org.apache.flink.util.ResourceGuard;
+
+import javax.annotation.Nonnegative;
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+import java.io.IOException;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+import static org.apache.flink.runtime.state.heap.SkipListUtils.HEAD_NODE;
+import static org.apache.flink.runtime.state.heap.SkipListUtils.NIL_NODE;
+import static org.apache.flink.runtime.state.heap.SkipListUtils.NIL_VALUE_POINTER;
+
+/**
+ * This class represents the snapshot of a {@link CopyOnWriteSkipListStateMap}.
+ *
+ * @param <K> type of key
+ * @param <N> type of namespace
+ * @param <S> type of state
+ */
+public class CopyOnWriteSkipListStateMapSnapshot<K, N, S>
+	extends StateMapSnapshot<K, N, S, CopyOnWriteSkipListStateMap<K, N, S>> {
+
+	/**
+	 * Version of the {@link CopyOnWriteSkipListStateMap} when this snapshot was created. This can be used to release the snapshot.
+	 */
+	private final int snapshotVersion;
+
+	/** The number of (non-null) entries in snapshotData. */
+	@Nonnegative
+	private final int numberOfEntriesInSnapshotData;
+
+	/**
+	 * This lease protects the state map resources.
+	 */
+	private final ResourceGuard.Lease lease;
+
+	/**
+	 * Creates a new {@link CopyOnWriteSkipListStateMap}.
+	 *
+	 * @param owningStateMap the {@link CopyOnWriteSkipListStateMap} for which this object represents a snapshot.
+	 * @param lease the lease protects the state map resources.
+	 */
+	CopyOnWriteSkipListStateMapSnapshot(
+		CopyOnWriteSkipListStateMap<K, N, S> owningStateMap,
+		ResourceGuard.Lease lease) {
+		super(owningStateMap);
+
+		this.snapshotVersion = owningStateMap.getStateMapVersion();
+		this.numberOfEntriesInSnapshotData = owningStateMap.size();
+		this.lease = lease;
+	}
+
+	/**
+	 * Returns the internal version of the when this snapshot was created.
+	 */
+	int getSnapshotVersion() {
+		return snapshotVersion;
+	}
+
+	@Override
+	public void release() {
+		owningStateMap.releaseSnapshot(this);
+		lease.close();
+	}
+
+	@Override
+	public void writeState(
+		TypeSerializer<K> keySerializer,
+		TypeSerializer<N> namespaceSerializer,
+		TypeSerializer<S> stateSerializer,
+		@Nonnull DataOutputView dov,
+		@Nullable StateSnapshotTransformer<S> stateSnapshotTransformer) throws IOException {
+		if (stateSnapshotTransformer == null) {
+			writeStateWithNoTransform(dov);
+		} else {
+			writeStateWithTransform(stateSerializer, dov, stateSnapshotTransformer);
+		}
+	}
+
+	private void writeStateWithNoTransform(@Nonnull DataOutputView dov) throws IOException {
+		dov.writeInt(numberOfEntriesInSnapshotData);
+		SnapshotNodeIterator nodeIterator = new SnapshotNodeIterator(true);
+		while (nodeIterator.hasNext()) {
+			Tuple2<Long, Long> tuple = nodeIterator.next();
+			writeKeyAndNamespace(tuple.f0, dov);
+			writeValue(tuple.f1, dov);
+		}
+	}
+
+	private void writeStateWithTransform(
+		TypeSerializer<S> stateSerializer,
+		@Nonnull DataOutputView dov,
+		@Nonnull StateSnapshotTransformer<S> stateSnapshotTransformer) throws IOException {
+		SkipListValueSerializer<S> skipListValueSerializer =
+			new SkipListValueSerializer<>(stateSerializer);
+
+		// 1. iterates nodes to get size after transform
+		SnapshotNodeIterator transformNodeIterator = new SnapshotNodeIterator(true);
+		int size = 0;
+		while (transformNodeIterator.hasNext()) {
+			Tuple2<Long, Long> tuple = transformNodeIterator.next();
+			S oldState = owningStateMap.helpGetState(tuple.f1, skipListValueSerializer);
+			S newState = stateSnapshotTransformer.filterOrTransform(oldState);
+			if (newState != null) {
+				size++;
+			}
+		}
+
+		dov.writeInt(size);
 
 Review comment:
   Here we need to get and write the element number first into the snapshot and then follows each element, so we cannot prevent the two while loop. And we have a similar logic in `CopyOnWriteStateMapSnapshot.writeState`, where the first loop is inside `CopyOnWriteStateMapSnapshot$TransformedSnapshotIterator.transform`

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