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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