HDFS-11449: libhdfs++: Log Datanode read size when reading from an HDFS block. Contributed by Xiaowei Zhu.

hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfspp/lib/fs/filehandle.cc

@@ -227,14 +227,15 @@ void FileHandleImpl::AsyncPreadSome(
 
   std::string dnIpAddr = chosen_dn.id().ipaddr();
   std::string dnHostName = chosen_dn.id().hostname();
-  LOG_DEBUG(kFileHandle, << "FileHandleImpl::AsyncPreadSome("
-            << FMT_THIS_ADDR << "), ...) Datanode hostname=" << dnHostName << ", IP Address=" << dnIpAddr
-            << ", file path=\"" << path_ << "\", offset=" << offset);
 
   uint64_t offset_within_block = offset - block->offset();
   uint64_t size_within_block = std::min<uint64_t>(
       block->b().numbytes() - offset_within_block, asio::buffer_size(buffers));
 
+  LOG_DEBUG(kFileHandle, << "FileHandleImpl::AsyncPreadSome("
+            << FMT_THIS_ADDR << "), ...) Datanode hostname=" << dnHostName << ", IP Address=" << dnIpAddr
+            << ", file path=\"" << path_ << "\", offset=" << offset << ", read size=" << size_within_block);
+
   // This is where we will put the logic for re-using a DN connection; we can
   //    steal the FileHandle's dn and put it back when we're done
   std::shared_ptr<DataNodeConnection> dn = CreateDataNodeConnection(io_service_, chosen_dn, &block->blocktoken());