[GitHub] [hadoop] steveloughran commented on a change in pull request #1869: HADOOP-16898. Batch listing of multiple directories to be an unstable interface

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steveloughran commented on a change in pull request #1869: HADOOP-16898. Batch listing of multiple directories to be an unstable interface
URL: https://github.com/apache/hadoop/pull/1869#discussion_r387724320
 
 

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 File path: hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/BatchListingOperations.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.hadoop.fs;
+
+import java.io.IOException;
+import java.util.List;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+
+/**
+ * Interface filesystems MAY implement to offer a batched list.
+ * If implemented, filesystems SHOULD declare
+ * {@link CommonPathCapabilities#FS_EXPERIMENTAL_BATCH_LISTING} to be a supported
+ * path capability.
+ */
+@InterfaceAudience.Public
+@InterfaceStability.Unstable
+public interface BatchListingOperations {
+
+  /**
+   * Batched listing API that returns {@link PartialListing}s for the
+   * passed Paths.
+   *
+   * @param paths List of paths to list.
+   * @return RemoteIterator that returns corresponding PartialListings.
+   * @throws IOException failure
+   */
+  RemoteIterator<PartialListing<FileStatus>> batchedListStatusIterator(
 
 Review comment:
   that's how it shoudl be done, though I'm not going to commit to the coding. Look at org.apache.hadoop.fs.FSBuilder, AbstractFSBuilderImpl and see how they are used in createFile & openFile. Most of the core work for the builder is there; we just need
   
   * a hasPathProperties probe for the new method (which we can chain through filters)
   * a method to create the builder for those FSs which implement
   * them to instatiate the work
   
   for an object store, you could use this as the base API for listing with just a single entry, at which point its an async list.

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