diff --git a/include/rabit/internal/engine.h b/include/rabit/internal/engine.h
index 79565218..81dee72d 100644
--- a/include/rabit/internal/engine.h
+++ b/include/rabit/internal/engine.h
@@ -158,8 +158,8 @@ class IEngine {
    * \param msg message to be printed in the tracker
    */
   virtual void TrackerPrint(const std::string &msg) = 0;
-  virtual void TrackerSetConfig(const std::string &key, const std::string &value) = 0;
-  virtual void TrackerGetConfig(const std::string& key, std::string* value) = 0;
+  virtual void TrackerSetConfig(const std::string &key, const int size, const void* value) = 0;
+  virtual void TrackerGetConfig(const std::string& key, const int size, void* value) = 0;
 };
 
 /*! \brief initializes the engine module */
diff --git a/include/rabit/internal/rabit-inl.h b/include/rabit/internal/rabit-inl.h
index 861861b3..3ad5ee11 100644
--- a/include/rabit/internal/rabit-inl.h
+++ b/include/rabit/internal/rabit-inl.h
@@ -142,7 +142,8 @@ inline void Broadcast(std::vector<DType> *sendrecv_data, int root, const char* c
     Broadcast(&(*sendrecv_data)[0], size * sizeof(DType), root, caller);
   }
 }
-inline void Broadcast(std::string *sendrecv_data, int root, const char* caller) {
+inline void Broadcast(std::string *sendrecv_data, int root, 
+  const char* caller) {
   size_t size = sendrecv_data->length();
   Broadcast(&size, sizeof(size), root, caller);
   if (sendrecv_data->length() != size) {
@@ -182,12 +183,12 @@ inline void TrackerPrint(const std::string &msg) {
   engine::GetEngine()->TrackerPrint(msg);
 }
 
-inline void TrackerSetConfig(const std::string &key, const std::string &value) {
-  engine::GetEngine()->TrackerSetConfig(key, value);
+inline void TrackerSetConfig(const std::string &key, const int bsize, const void *value) {
+  engine::GetEngine()->TrackerSetConfig(key, bsize, value);
 }
 
-inline void TrackerGetConfig(const std::string &key, std::string* value) {
-  engine::GetEngine()->TrackerGetConfig(key, value);
+inline void TrackerGetConfig(const std::string &key, const int bsize, void *value) {
+  engine::GetEngine()->TrackerGetConfig(key, bsize, value);
 }
 
 #ifndef RABIT_STRICT_CXX98_
@@ -202,7 +203,7 @@ inline void TrackerPrintf(const char *fmt, ...) {
   TrackerPrint(msg);
 }
 
-inline void TrackerSetConfig(const char *key, const char *value, ...) {
+inline void TrackerSetConfig(const char *key, const int bsize, const void *value, ...) {
   const int kPrintBuffer = 1 << 10;
   std::string k(kPrintBuffer, '\0'), v(kPrintBuffer, '\0');
 
@@ -210,28 +211,22 @@ inline void TrackerSetConfig(const char *key, const char *value, ...) {
   va_start(args1, key);
   va_start(args2, value);
   vsnprintf(&k[0], kPrintBuffer, key, args1);
-  vsnprintf(&v[0], kPrintBuffer, value, args2);
   va_end(args1);
   va_end(args2);
   k.resize(strlen(k.c_str()));
-  v.resize(strlen(v.c_str()));
-  engine::GetEngine()->TrackerSetConfig(k, v);
+  engine::GetEngine()->TrackerSetConfig(k, bsize, value);
 }
 
-inline void TrackerGetConfig(const char *key, char* value, ...) {
+inline void TrackerGetConfig(const char *key, const int bsize, void* value, ...) {
   const int kPrintBuffer = 1 << 10;
   std::string k(kPrintBuffer, '\0'), v(kPrintBuffer, '\0');
 
-  va_list args1, args2;
+  va_list args1;
   va_start(args1, key);
-  va_start(args2, value);
   vsnprintf(&k[0], kPrintBuffer, key, args1);
-  vsnprintf(&v[0], kPrintBuffer, value, args2);
   va_end(args1);
-  va_end(args2);
   k.resize(strlen(k.c_str()));
-  v.resize(strlen(v.c_str()));
-  engine::GetEngine()->TrackerGetConfig(k, &v);
+  engine::GetEngine()->TrackerGetConfig(k, bsize, value);
 }
 #endif  // RABIT_STRICT_CXX98_
 // load latest check point
diff --git a/include/rabit/rabit.h b/include/rabit/rabit.h
index cac237d8..ca0e5c9a 100644
--- a/include/rabit/rabit.h
+++ b/include/rabit/rabit.h
@@ -105,13 +105,13 @@ inline void TrackerPrint(const std::string &msg);
  * \param key configuration key
  * \param value value of config
  */
-inline void TrackerSetConfig(const std::string &key, const std::string &value);
+inline void TrackerSetConfig(const std::string &key, const int bsize, const void* value);
 /*!
  * \brief get config to tracker,
  * \param key configuration key
  * \param value value of config
  */
-inline void TrackerGetConfig(const std::string &key, std::string* value);
+inline void TrackerGetConfig(const std::string &key, const int bsize, void* value);
 
 #ifndef RABIT_STRICT_CXX98_
 /*!
@@ -127,13 +127,13 @@ inline void TrackerPrintf(const char *fmt, ...);
  * \param key configuration key
  * \param value value of config
  */
-inline void TrackerSetConfig(const char *key, const char *value, ...);
+inline void TrackerSetConfig(const char *key, const int bsize, const void* value, ...);
 /*!
  * \brief get config to tracker,
  * \param key configuration key
  * \param value value of config
  */
-inline void TrackerGetConfig(const char *key, char* value, ...);
+inline void TrackerGetConfig(const char *key, const int bsize, void* value, ...);
 #endif  // RABIT_STRICT_CXX98_
 /*!
  * \brief broadcasts a memory region to every node from the root
@@ -143,7 +143,8 @@ inline void TrackerGetConfig(const char *key, char* value, ...);
  * \param size the data size
  * \param root the process root
  */
-inline void Broadcast(void *sendrecv_data, size_t size, int root, const char* caller = __builtin_FUNCTION());
+inline void Broadcast(void *sendrecv_data, size_t size, int root, 
+  const char* caller = __builtin_FUNCTION());
 /*!
  * \brief broadcasts an std::vector<DType> to every node from root
  * \param sendrecv_data the pointer to send/receive vector,
@@ -153,14 +154,16 @@ inline void Broadcast(void *sendrecv_data, size_t size, int root, const char* ca
  *               that can be directly transmitted by sending the sizeof(DType)
  */
 template<typename DType>
-inline void Broadcast(std::vector<DType> *sendrecv_data, int root, const char* caller = __builtin_FUNCTION());
+inline void Broadcast(std::vector<DType> *sendrecv_data, int root, 
+  const char* caller = __builtin_FUNCTION());
 /*!
  * \brief broadcasts a std::string to every node from the root
  * \param sendrecv_data the pointer to the send/receive buffer,
  *        for the receiver, the vector does not need to be pre-allocated
  * \param root the process root
  */
-inline void Broadcast(std::string *sendrecv_data, int root, const char* caller = __builtin_FUNCTION());
+inline void Broadcast(std::string *sendrecv_data, int root, 
+  const char* caller = __builtin_FUNCTION());
 /*!
  * \brief performs in-place Allreduce on sendrecvbuf
  *        this function is NOT thread-safe
@@ -185,7 +188,8 @@ inline void Broadcast(std::string *sendrecv_data, int root, const char* caller =
 template<typename OP, typename DType>
 inline void Allreduce(DType *sendrecvbuf, size_t count,
                       void (*prepare_fun)(void *) = NULL,
-                      void *prepare_arg = NULL, const char* caller = __builtin_FUNCTION());
+                      void *prepare_arg = NULL, 
+                      const char* caller = __builtin_FUNCTION());
 // C++11 support for lambda prepare function
 #if DMLC_USE_CXX11
 /*!
@@ -214,7 +218,8 @@ inline void Allreduce(DType *sendrecvbuf, size_t count,
  */
 template<typename OP, typename DType>
 inline void Allreduce(DType *sendrecvbuf, size_t count,
-                      std::function<void()> prepare_fun, const char* caller = __builtin_FUNCTION());
+                      std::function<void()> prepare_fun, 
+                      const char* caller = __builtin_FUNCTION());
 #endif  // C++11
 /*!
  * \brief loads the latest check point
diff --git a/src/allreduce_base.cc b/src/allreduce_base.cc
index 3c184efe..b11527ad 100644
--- a/src/allreduce_base.cc
+++ b/src/allreduce_base.cc
@@ -146,19 +146,20 @@ void AllreduceBase::TrackerPrint(const std::string &msg) {
   tracker.Close();
 }
 
-void AllreduceBase::TrackerSetConfig(const std::string &key, const std::string &value) {
+void AllreduceBase::TrackerSetConfig(const std::string &key, const int bytesize, const void* value) {
   utils::TCPSocket tracker = this->ConnectTracker();
   tracker.SendStr(std::string("set"));
   tracker.SendStr(key);
-  tracker.SendStr(value);
+  tracker.Send(&bytesize, sizeof(int));
+  tracker.SendAll(value, bytesize);
   tracker.Close();
 }
 
-void AllreduceBase::TrackerGetConfig(const std::string &key, std::string* value) {
+void AllreduceBase::TrackerGetConfig(const std::string &key, const int bytesize, void* value) {
   utils::TCPSocket tracker = this->ConnectTracker();
   tracker.SendStr(std::string("get"));
   tracker.SendStr(key);
-  tracker.RecvStr(value);
+  tracker.RecvAll(value, bytesize);
   tracker.Close();
 }
 
diff --git a/src/allreduce_base.h b/src/allreduce_base.h
index da41fda5..29472855 100644
--- a/src/allreduce_base.h
+++ b/src/allreduce_base.h
@@ -54,8 +54,8 @@ class AllreduceBase : public IEngine {
    * \param msg message to be printed in the tracker
    */
   virtual void TrackerPrint(const std::string &msg);
-  virtual void TrackerSetConfig(const std::string &key, const std::string &value);
-  virtual void TrackerGetConfig(const std::string& key, std::string* value);
+  virtual void TrackerSetConfig(const std::string &key, const int bytesize, const void* value);
+  virtual void TrackerGetConfig(const std::string &key, const int bytesize, void* value);
 
   /*! \brief get rank */
   virtual int GetRank(void) const {
diff --git a/src/allreduce_robust.cc b/src/allreduce_robust.cc
index f3c77568..e56c3b52 100644
--- a/src/allreduce_robust.cc
+++ b/src/allreduce_robust.cc
@@ -92,6 +92,7 @@ void AllreduceRobust::Allreduce(void *sendrecvbuf_,
     if (prepare_fun != NULL) prepare_fun(prepare_arg);
     return;
   }
+
   bool recovered = RecoverExec(sendrecvbuf_, type_nbytes * count, 0, seq_counter);
   // now we are free to remove the last result, if any
   if (resbuf.LastSeqNo() != -1 &&