[GitHub] [hadoop] steveloughran commented on a change in pull request #1830: HADOOP-11867: Add gather API to file system.

[GitBox <gi...@apache.org>]

steveloughran commented on a change in pull request #1830: HADOOP-11867: Add gather API to file system.
URL: https://github.com/apache/hadoop/pull/1830#discussion_r374652628
 
 

 ##########
 File path: hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/PositionedReadable.java
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 @@ -85,4 +89,37 @@ void readFully(long position, byte[] buffer, int offset, int length)
    * the read operation completed
    */
   void readFully(long position, byte[] buffer) throws IOException;
+
+  /**
+   * What is the smallest reasonable seek?
+   * @return the minimum number of bytes
+   */
+  default int minimumReasonableSeek() {
+    return 4 * 1024;
+  }
+
+  /**
+   * What is the largest size that we should group ranges together as?
+   * @return the number of bytes to read at once
+   */
+  default int maximumReadSize() {
+    return 1024 * 1024;
+  }
+
+  /**
+   * Read fully a list of file ranges asynchronously from this file.
+   * The default iterates through the ranges to read each synchronously, but
+   * the intent is that FSDataInputStream subclasses can make more efficient
+   * readers.
+   * As a result of the call, each range will have FileRange.setData(CompletableFuture)
+   * called with a future that when complete will have a ByteBuffer with the
+   * data from the file's range.
+   * @param ranges the byte ranges to read
+   * @param allocate the function to allocate ByteBuffer
+   */
+  default void readAsync(List<? extends FileRange> ranges,
 
 Review comment:
   I really like `default`; makes maintenance of interfaces way less brittle, as now we can add methods. ironic it took a need from Oracle themselves to force the feature to go in

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