HADOOP-4614. Lazily open segments when merging map spills to avoid using

too many file descriptors. Contributed by Yuri Pradkin.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.19@720701 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -1026,6 +1026,9 @@ Release 0.18.3 - Unreleased
     HADOOP-4659. Root cause of connection failure is being ost to code that
     uses it for delaying startup. (Steve Loughran and Hairong via hairong)
 
+    HADOOP-4614. Lazily open segments when merging map spills to avoid using
+    too many file descriptors. (Yuri Pradkin via cdouglas)
+
 Release 0.18.2 - 2008-11-03
 
   BUG FIXES

src/mapred/org/apache/hadoop/mapred/MapTask.java

@@ -1234,27 +1234,23 @@ class MapTask extends Task {
             new ArrayList<Segment<K, V>>(numSpills);
           TaskAttemptID mapId = getTaskID();
           for(int i = 0; i < numSpills; i++) {
-            IndexRecord indexRecord = 
+            final IndexRecord indexRecord = 
               getIndexInformation(mapId, i, parts);
 
             long segmentOffset = indexRecord.startOffset;
-            long rawSegmentLength = indexRecord.rawLength;
             long segmentLength = indexRecord.partLength;
 
-            FSDataInputStream in = rfs.open(filename[i]);
-            in.seek(segmentOffset);
-
             Segment<K, V> s = 
-              new Segment<K, V>(new Reader<K, V>(job, in, segmentLength, codec),
-                                true);
+              new Segment<K, V>(job, rfs, filename[i], segmentOffset, 
+                                segmentLength, codec, true);
             segmentList.add(i, s);
             
             if (LOG.isDebugEnabled()) {
+              long rawSegmentLength = indexRecord.rawLength;
               LOG.debug("MapId=" + mapId + " Reducer=" + parts +
                   "Spill =" + i + "(" + segmentOffset + ","+ 
                         rawSegmentLength + ", " + segmentLength + ")");
             }
-            indexRecord = null;
           }
           
           //merge

src/mapred/org/apache/hadoop/mapred/Merger.java

@@ -26,6 +26,7 @@ import java.util.List;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FSDataInputStream;
 import org.apache.hadoop.fs.ChecksumFileSystem;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.LocalDirAllocator;
@@ -124,17 +125,25 @@ class Merger {
     Path file = null;
     boolean preserve = false;
     CompressionCodec codec = null;
+    long segmentOffset = 0;
     long segmentLength = -1;
+
     
     public Segment(Configuration conf, FileSystem fs, Path file,
                    CompressionCodec codec, boolean preserve) throws IOException {
+      this(conf, fs, file, 0, fs.getFileStatus(file).getLen(), codec, preserve);
+    }
+
+    public Segment(Configuration conf, FileSystem fs, Path file,
+                   long segmentOffset, long segmentLength, 
+                   CompressionCodec codec, boolean preserve) throws IOException {
       this.conf = conf;
       this.fs = fs;
       this.file = file;
       this.codec = codec;
       this.preserve = preserve;
-      
-      this.segmentLength = fs.getFileStatus(file).getLen();
+      this.segmentLength = segmentLength;
+      this.segmentOffset = segmentOffset;
     }
     
     public Segment(Reader<K, V> reader, boolean preserve) {
@@ -146,7 +155,9 @@ class Merger {
 
     private void init() throws IOException {
       if (reader == null) {
-        reader = new Reader<K, V>(conf, fs, file, codec);
+        FSDataInputStream in = fs.open(file);
+        in.seek(segmentOffset);
+        reader = new Reader<K, V>(conf, in, segmentLength, codec);
       }
     }