MAPREDUCE-18. Puts some checks to detect cases where jetty serves up incorrect output during shuffle. Contributed by Ravi Gummadi.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.20@794638 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -181,6 +181,9 @@ Release 0.20.1 - Unreleased
     MAPREDUCE-465. Fix a bug in MultithreadedMapRunner. (Amareshwari 
     Sriramadasu via sharad)
 
+    MAPREDUCE-18. Puts some checks to detect cases where jetty serves up
+    incorrect output during shuffle. (Ravi Gummadi via ddas)
+
 Release 0.20.0 - 2009-04-15
 
   INCOMPATIBLE CHANGES

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

@@ -47,5 +47,15 @@ interface MRConstants {
    */
   public static final String RAW_MAP_OUTPUT_LENGTH = "Raw-Map-Output-Length";
 
+  /**
+   * The map task from which the map output data is being transferred
+   */
+  public static final String FROM_MAP_TASK = "from-map-task";
+  
+  /**
+   * The reduce task number for which this map output is being transferred
+   */
+  public static final String FOR_REDUCE_TASK = "for-reduce-task";
+  
   public static final String WORKDIR = "work";
 }

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

@@ -1259,7 +1259,8 @@ class ReduceTask extends Task {
         Path tmpMapOutput = new Path(filename+"-"+id);
         
         // Copy the map output
-        MapOutput mapOutput = getMapOutput(loc, tmpMapOutput);
+        MapOutput mapOutput = getMapOutput(loc, tmpMapOutput,
+                                           reduceId.getTaskID().getId());
         if (mapOutput == null) {
           throw new IOException("Failed to fetch map-output for " + 
                                 loc.getTaskAttemptId() + " from " + 
@@ -1341,24 +1342,60 @@ class ReduceTask extends Task {
        * @throws IOException when something goes wrong
        */
       private MapOutput getMapOutput(MapOutputLocation mapOutputLoc, 
-                                     Path filename)
+                                     Path filename, int reduce)
       throws IOException, InterruptedException {
         // Connect
         URLConnection connection = 
           mapOutputLoc.getOutputLocation().openConnection();
         InputStream input = getInputStream(connection, STALLED_COPY_TIMEOUT,
                                            DEFAULT_READ_TIMEOUT); 
-
-        //We will put a file in memory if it meets certain criteria:
-        //1. The size of the (decompressed) file should be less than 25% of 
-        //    the total inmem fs
-        //2. There is space available in the inmem fs
-
+        
+        // Validate header from map output
+        TaskAttemptID mapId = null;
+        try {
+          mapId =
+            TaskAttemptID.forName(connection.getHeaderField(FROM_MAP_TASK));
+        } catch (IllegalArgumentException ia) {
+          LOG.warn("Invalid map id ", ia);
+          return null;
+        }
+        TaskAttemptID expectedMapId = mapOutputLoc.getTaskAttemptId();
+        if (!mapId.equals(expectedMapId)) {
+          LOG.warn("data from wrong map:" + mapId +
+              " arrived to reduce task " + reduce +
+              ", where as expected map output should be from " + expectedMapId);
+          return null;
+        }
+        
         long decompressedLength = 
           Long.parseLong(connection.getHeaderField(RAW_MAP_OUTPUT_LENGTH));  
         long compressedLength = 
           Long.parseLong(connection.getHeaderField(MAP_OUTPUT_LENGTH));
 
+        if (compressedLength < 0 || decompressedLength < 0) {
+          LOG.warn(getName() + " invalid lengths in map output header: id: " +
+              mapId + " compressed len: " + compressedLength +
+              ", decompressed len: " + decompressedLength);
+          return null;
+        }
+        int forReduce =
+          (int)Integer.parseInt(connection.getHeaderField(FOR_REDUCE_TASK));
+        
+        if (forReduce != reduce) {
+          LOG.warn("data for the wrong reduce: " + forReduce +
+              " with compressed len: " + compressedLength +
+              ", decompressed len: " + decompressedLength +
+              " arrived to reduce task " + reduce);
+          return null;
+        }
+        LOG.info("header: " + mapId + ", compressed len: " + compressedLength +
+                 ", decompressed len: " + decompressedLength);
+
+        //We will put a file in memory if it meets certain criteria:
+        //1. The size of the (decompressed) file should be less than 25% of 
+        //    the total inmem fs
+        //2. There is space available in the inmem fs
+        
         // Check if this map-output can be saved in-memory
         boolean shuffleInMemory = ramManager.canFitInMemory(decompressedLength); 
 

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

@@ -2870,9 +2870,13 @@ public class TaskTracker
          * Read the index file to get the information about where
          * the map-output for the given reducer is available. 
          */
-       IndexRecord info = 
+        IndexRecord info = 
           tracker.indexCache.getIndexInformation(mapId, reduce,indexFileName);
           
+        //set the custom "from-map-task" http header to the map task from which
+        //the map output data is being transferred
+        response.setHeader(FROM_MAP_TASK, mapId);
+        
         //set the custom "Raw-Map-Output-Length" http header to 
         //the raw (decompressed) length
         response.setHeader(RAW_MAP_OUTPUT_LENGTH,
@@ -2883,6 +2887,10 @@ public class TaskTracker
         response.setHeader(MAP_OUTPUT_LENGTH,
             Long.toString(info.partLength));
 
+        //set the custom "for-reduce-task" http header to the reduce task number
+        //for which this map output is being transferred
+        response.setHeader(FOR_REDUCE_TASK, Integer.toString(reduce));
+        
         //use the same buffersize as used for reading the data from disk
         response.setBufferSize(MAX_BYTES_TO_READ);