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https://issues.apache.org/jira/browse/FLINK-2991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15140651#comment-15140651
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ASF GitHub Bot commented on FLINK-2991:
---------------------------------------
Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/1605#discussion_r52444796
--- Diff:
flink-contrib/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBFoldingState.java
---
@@ -0,0 +1,175 @@
+/*
+ * 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.functions.FoldFunction;
+import org.apache.flink.api.common.state.FoldingState;
+import org.apache.flink.api.common.state.FoldingStateDescriptor;
+import org.apache.flink.api.common.state.ReducingState;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.core.memory.DataInputViewStreamWrapper;
+import org.apache.flink.core.memory.DataOutputViewStreamWrapper;
+import org.apache.flink.runtime.state.AbstractStateBackend;
+import org.apache.flink.runtime.state.KvState;
+import org.apache.flink.runtime.state.KvStateSnapshot;
+import org.rocksdb.RocksDBException;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.net.URI;
+
+import static java.util.Objects.requireNonNull;
+
+/**
+ * {@link ReducingState} implementation that stores state in RocksDB.
+ *
+ * @param <K> The type of the key.
+ * @param <N> The type of the namespace.
+ * @param <T> The type of the values that can be folded into the state.
+ * @param <ACC> The type of the value in the folding state.
+ * @param <Backend> The type of the backend that snapshots this key/value
state.
+ */
+public class RocksDBFoldingState<K, N, T, ACC, Backend extends
AbstractStateBackend>
+ extends AbstractRocksDBState<K, N, FoldingState<T, ACC>,
FoldingStateDescriptor<T, ACC>, Backend>
+ implements FoldingState<T, ACC> {
+
+ /** Serializer for the values */
+ private final TypeSerializer<ACC> valueSerializer;
+
+ /** This holds the name of the state and can create an initial default
value for the state. */
+ protected final FoldingStateDescriptor<T, ACC> stateDesc;
+
+ /** User-specified fold function */
+ private final FoldFunction<T, ACC> foldFunction;
+
+ /**
+ * Creates a new {@code RocksDBFoldingState}.
+ *
+ * @param keySerializer The serializer for the keys.
+ * @param namespaceSerializer The serializer for the namespace.
+ * @param stateDesc The state identifier for the state. This contains
name
+ * and can create a default state value.
+ * @param dbPath The path on the local system where RocksDB data should
be stored.
+ */
+ protected RocksDBFoldingState(TypeSerializer<K> keySerializer,
+ TypeSerializer<N> namespaceSerializer,
+ FoldingStateDescriptor<T, ACC> stateDesc,
+ File dbPath,
+ String backupPath) {
+ super(keySerializer, namespaceSerializer, dbPath, backupPath);
+ this.stateDesc = requireNonNull(stateDesc);
+ this.valueSerializer = stateDesc.getSerializer();
+ this.foldFunction = stateDesc.getFoldFunction();
+ }
+
+ protected RocksDBFoldingState(TypeSerializer<K> keySerializer,
--- End diff --
java docs
> Extend Window Operators to Allow Efficient Fold Operation
> ---------------------------------------------------------
>
> Key: FLINK-2991
> URL: https://issues.apache.org/jira/browse/FLINK-2991
> Project: Flink
> Issue Type: Improvement
> Components: Streaming
> Reporter: Aljoscha Krettek
> Assignee: Aljoscha Krettek
>
> Right now, a window fold is implemented as a WindowFunction that gets all the
> elements as input. No pre-aggregation is performed. The window operator
> should be extended to also allow the fold to also be pre-aggregated.
> This requires changing the signature of the {{WindowBuffer}} so that it can
> emit a type other than the input type.
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