[GitHub] klion26 commented on a change in pull request #6777: [FLINK-10461] [State Backends, Checkpointing] Speed up download files when restore from DFS

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klion26 commented on a change in pull request #6777: [FLINK-10461] [State Backends, Checkpointing] Speed up download files when restore from DFS
URL: https://github.com/apache/flink/pull/6777#discussion_r238623643
 
 

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 File path: flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDbStateDataTransfer.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.contrib.streaming.state;
+
+import org.apache.flink.core.fs.CloseableRegistry;
+import org.apache.flink.core.fs.FSDataInputStream;
+import org.apache.flink.core.fs.FSDataOutputStream;
+import org.apache.flink.core.fs.FileSystem;
+import org.apache.flink.core.fs.Path;
+import org.apache.flink.runtime.concurrent.FutureUtils;
+import org.apache.flink.runtime.state.IncrementalKeyedStateHandle;
+import org.apache.flink.runtime.state.StateHandleID;
+import org.apache.flink.runtime.state.StreamStateHandle;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+/**
+ * Data transfer utils for RocksDbKeyedStateBackend.
+ */
+public class RocksDbStateDataTransfer {
+
+	public static void transferAllStateDataToDirectory(
+		IncrementalKeyedStateHandle restoreStateHandle,
+		Path dest,
+		int restoringThreadNum,
+		CloseableRegistry closeableRegistry) throws Exception {
+
+		final Map<StateHandleID, StreamStateHandle> sstFiles =
+			restoreStateHandle.getSharedState();
+		final Map<StateHandleID, StreamStateHandle> miscFiles =
+			restoreStateHandle.getPrivateState();
+
+		downloadDataForAllStateHandles(sstFiles, dest, restoringThreadNum, closeableRegistry);
+		downloadDataForAllStateHandles(miscFiles, dest, restoringThreadNum, closeableRegistry);
+	}
+
+	/**
+	 * Copies all the files from the given stream state handles to the given path, renaming the files w.r.t. their
+	 * {@link StateHandleID}.
+	 */
+	private static void downloadDataForAllStateHandles(
+		Map<StateHandleID, StreamStateHandle> stateHandleMap,
+		Path restoreInstancePath,
+		int restoringThreadNum,
+		CloseableRegistry closeableRegistry
+		) throws Exception {
+
+		List<Runnable> runnables = createDownloadRunnables(stateHandleMap, restoreInstancePath, closeableRegistry);
+
+		if (enableMultiThreadDownload(restoringThreadNum)) {
+			runTransferWithMultipleThreads(runnables, restoringThreadNum, closeableRegistry);
+		} else {
+			runTransferWithSingleThread(runnables);
+		}
 
 Review comment:
   In my opinion, if `restoringThreadNum == 1`, we should run the `runnables` in current thread other than in the executorService, which is the current behavior. What do you think about it?

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