HDFS-9576: HTrace: collect position/length information on read operations (zhz via cmccabe)

(cherry picked from commit 7905788db94d560e6668af0d4bed22b326961aaf)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClient.java

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClient.java

@@ -2947,6 +2947,25 @@ public class DFSClient implements java.io.Closeable, RemotePeerFactory,
     return scope;
   }
 
+  /**
+   * Full detailed tracing for read requests: path, position in the file,
+   * and length.
+   *
+   * @param reqLen requested length
+   */
+  TraceScope newReaderTraceScope(String description, String path, long pos,
+      int reqLen) {
+    TraceScope scope = newPathTraceScope(description, path);
+    scope.addKVAnnotation("pos", Long.toString(pos));
+    scope.addKVAnnotation("reqLen", Integer.toString(reqLen));
+    return scope;
+  }
+
+  /** Add the returned length info to the scope. */
+  void addRetLenToReaderScope(TraceScope scope, int retLen) {
+    scope.addKVAnnotation("retLen", Integer.toString(retLen));
+  }
+
   Tracer getTracer() {
     return tracer;
   }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java

@@ -974,18 +974,29 @@ public class DFSInputStream extends FSInputStream
   public synchronized int read(@Nonnull final byte buf[], int off, int len)
       throws IOException {
     ReaderStrategy byteArrayReader = new ByteArrayStrategy(buf);
-    try (TraceScope ignored =
-             dfsClient.newPathTraceScope("DFSInputStream#byteArrayRead", src)) {
-      return readWithStrategy(byteArrayReader, off, len);
+    try (TraceScope scope =
+             dfsClient.newReaderTraceScope("DFSInputStream#byteArrayRead",
+                 src, getPos(), len)) {
+      int retLen = readWithStrategy(byteArrayReader, off, len);
+      if (retLen < len) {
+        dfsClient.addRetLenToReaderScope(scope, retLen);
+      }
+      return retLen;
     }
   }
 
   @Override
   public synchronized int read(final ByteBuffer buf) throws IOException {
     ReaderStrategy byteBufferReader = new ByteBufferStrategy(buf);
-    try (TraceScope ignored =
-             dfsClient.newPathTraceScope("DFSInputStream#byteBufferRead", src)){
-      return readWithStrategy(byteBufferReader, 0, buf.remaining());
+    int reqLen = buf.remaining();
+    try (TraceScope scope =
+             dfsClient.newReaderTraceScope("DFSInputStream#byteBufferRead",
+                 src, getPos(), reqLen)){
+      int retLen = readWithStrategy(byteBufferReader, 0, reqLen);
+      if (retLen < reqLen) {
+        dfsClient.addRetLenToReaderScope(scope, retLen);
+      }
+      return retLen;
     }
   }
 
@@ -1461,9 +1472,14 @@ public class DFSInputStream extends FSInputStream
   @Override
   public int read(long position, byte[] buffer, int offset, int length)
       throws IOException {
-    try (TraceScope ignored = dfsClient.
-        newPathTraceScope("DFSInputStream#byteArrayPread", src)) {
-      return pread(position, buffer, offset, length);
+    try (TraceScope scope = dfsClient.
+        newReaderTraceScope("DFSInputStream#byteArrayPread",
+            src, position, length)) {
+      int retLen = pread(position, buffer, offset, length);
+      if (retLen < length) {
+        dfsClient.addRetLenToReaderScope(scope, retLen);
+      }
+      return retLen;
     }
   }
 

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -42,6 +42,9 @@ Release 2.9.0 - UNRELEASED
     HDFS-9624. DataNode start slowly due to the initial DU command operations.
     (Lin Yiqun via wang)
 
+    HDFS-9576: HTrace: collect position/length information on read operations
+    (zhz via cmccabe)
+
   OPTIMIZATIONS
 
   BUG FIXES