[GitHub] [flink] akalash commented on a change in pull request #18341: [FLINK-25194] Implement an API for duplicating artefacts

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akalash commented on a change in pull request #18341:
URL: https://github.com/apache/flink/pull/18341#discussion_r783176332



##########
File path: flink-runtime/src/main/java/org/apache/flink/runtime/state/CheckpointStreamFactory.java
##########
@@ -39,4 +40,31 @@
      */
     CheckpointStateOutputStream createCheckpointStateOutputStream(CheckpointedStateScope scope)
             throws IOException;
+
+    /**
+     * Tells if we can duplicate the given {@link StreamStateHandle} into the path corresponding to
+     * the given {@link CheckpointedStateScope}.
+     *
+     * <p>This should be a rather cheap operation, preferably not involving any remote accesses.
+     *
+     * @param stateHandle The handle to duplicate
+     * @param scope Scope determining the location to duplicate into
+     * @return true, if we can perform the duplication
+     */
+    boolean canFastDuplicate(StreamStateHandle stateHandle, CheckpointedStateScope scope)
+            throws IOException;
+
+    /**
+     * Duplicates {@link StreamStateHandle} into the path corresponding to * the given {@link
+     * CheckpointedStateScope}.
+     *
+     * <p>You should first check if you can duplicate with {@link
+     * #canFastDuplicate(StreamStateHandle, CheckpointedStateScope)}.
+     *
+     * @param stateHandles The handles to duplicate
+     * @param scope Scope determining the location to duplicate into
+     * @return The duplicated handle
+     */
+    List<StreamStateHandle> duplicate(

Review comment:
       I want to share my concern about matching the names of methods and class. It is not clear why *Factory duplicate something when Factory should only create something. I understand that creating streams and duplicating files are kind of one-level things but maybe we think about renaming the class?

##########
File path: flink-core/src/main/java/org/apache/flink/core/fs/DuplicatingFileSystem.java
##########
@@ -0,0 +1,74 @@
+/*
+ * 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.core.fs;
+
+import java.io.IOException;
+import java.util.List;
+
+/**
+ * An extension interface for {@link FileSystem FileSystems} that can perform cheap DFS side
+ * duplicate operation. Such an operation can improve the time required for creating cheaply
+ * independent snapshots from incremental snapshots.
+ */
+public interface DuplicatingFileSystem {

Review comment:
       Right now, we get FileSystem from Path#getFileSystem. Do I understand correctly that we will need to rewrite this code as well?




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