AVRO-3594. openFile() API through shim

Change-Id: Ie7099208b601a08823775e901359a6727f0c6fe6

lang/java/mapred/src/main/java/org/apache/avro/mapred/FsInput.java

@@ -22,12 +22,15 @@
 import java.io.IOException;
 
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.FSDataInputStream;
 
 import org.apache.avro.file.SeekableInput;
 
+import static org.apache.hadoop.fs.Options.OpenFileOptions.FS_OPTION_OPENFILE_READ_POLICY;
+import static org.apache.hadoop.fs.Options.OpenFileOptions.FS_OPTION_OPENFILE_READ_POLICY_ADAPTIVE;
 import static org.apache.hadoop.util.functional.FutureIO.awaitFuture;
 
 /** Adapt an {@link FSDataInputStream} to {@link SeekableInput}. */
@@ -42,16 +45,19 @@ public FsInput(Path path, Configuration conf) throws IOException {
 
   /** Construct given a path and a {@code FileSystem}. */
   public FsInput(Path path, FileSystem fileSystem) throws IOException {
-    this.len = fileSystem.getFileStatus(path).getLen();
-    // use the hadoop 3.3.0 openFile API and specify length
+    final FileStatus st = fileSystem.getFileStatus(path);
+    this.len = st.getLen();
+    // use the hadoop 3.3.0 openFile API, pass in status
     // and read policy. object stores can use these to
     // optimize read performance.
     // the read policy "adaptive" means "start sequential but
-    // go to random IO after backwards seeks"
+    // go to random IO when considered better"
     // Filesystems which don't recognize the options will ignore them
-
-    this.stream = awaitFuture(fileSystem.openFile(path).opt("fs.option.openfile.read.policy", "adaptive")
-        .opt("fs.option.openfile.length", Long.toString(len)).build());
+    // Importantly deployments which have switched the default read policy to
+    // "random"
+    // will not suffer when reading large avro files.
+    this.stream = awaitFuture(fileSystem.openFile(path)
+        .opt(FS_OPTION_OPENFILE_READ_POLICY, FS_OPTION_OPENFILE_READ_POLICY_ADAPTIVE).withFileStatus(st).build());
   }
 
   @Override