diff --git a/arangod/Pregel/Conductor.cpp b/arangod/Pregel/Conductor.cpp
index 309befe370..9b4eea601b 100755
--- a/arangod/Pregel/Conductor.cpp
+++ b/arangod/Pregel/Conductor.cpp
@@ -24,31 +24,30 @@
 #include "Utils.h"
 
 #include "Basics/MutexLocker.h"
+#include "Basics/StringUtils.h"
 #include "Utils/SingleCollectionTransaction.h"
 #include "Utils/StandaloneTransactionContext.h"
 #include "Cluster/ClusterInfo.h"
 #include "Cluster/ClusterComm.h"
+#include "VocBase/LogicalCollection.h"
 #include "VocBase/ticks.h"
 #include "VocBase/vocbase.h"
 
 #include <velocypack/Iterator.h>
 #include <velocypack/velocypack-aliases.h>
 
-using namespace std;
 using namespace arangodb;
 using namespace arangodb::pregel;
 
-Conductor::Conductor(int executionNumber,
-                     //TRI_vocbase_t *vocbase,
-                     std::string const&vertexCollection,
-                     CollectionID vertexCollectionID,
-                     std::string const& edgeCollection,
+Conductor::Conductor(unsigned int executionNumber,
+                     TRI_vocbase_t *vocbase,
+                     std::shared_ptr<LogicalCollection> vertexCollection,
+                     std::shared_ptr<LogicalCollection> edgeCollection,
                      std::string const& algorithm) :
+_vocbaseGuard(vocbase),
 _executionNumber(executionNumber),
-//_vocbase(vocbase),
 _vertexCollection(vertexCollection),
 _edgeCollection(edgeCollection),
-_vertexCollectionID(vertexCollectionID),
 _algorithm(algorithm) {
   
   bool isCoordinator = ServerState::instance()->isCoordinator();
@@ -56,56 +55,106 @@ _algorithm(algorithm) {
   LOG(INFO) << "constructed conductor";
 }
 
+static void printResults(std::vector<ClusterCommRequest> &requests) {
+  for (auto const& req : requests) {
+    auto& res = req.result;
+    if (res.status == CL_COMM_RECEIVED) {
+      LOG(INFO) << res.answer->payload().toJson();
+    }
+  }
+}
+
+
 void Conductor::start() {
+  ClusterComm* cc = ClusterComm::instance();
+  std::unordered_map<ServerID, std::vector<ShardID>> vertexServerMap, edgeServerMap;
+  resolveWorkerServers(vertexServerMap, edgeServerMap);
+  
+  std::string const baseUrl = Utils::baseUrl(_vocbaseGuard.vocbase());
+  
   _globalSuperstep = 0;
   _state = ExecutionState::RUNNING;
+  _dbServerCount = vertexServerMap.size();
+  _responseCount = 0;
+  _doneCount = 0;
+  if (vertexServerMap.size() != edgeServerMap.size()) {
+    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_BAD_PARAMETER,
+                                   "Vertex and edge collections are not shared correctly");
+  }
   
-  string coordinatorId = ServerState::instance()->getId();
+  std::string coordinatorId = ServerState::instance()->getId();
   LOG(INFO) << "My id: " << coordinatorId;
-  
-  VPackBuilder b;
-  b.openObject();
-  b.add(Utils::executionNumberKey, VPackValue(_executionNumber));
-  b.add(Utils::coordinatorIdKey, VPackValue(coordinatorId));
-  b.add(Utils::vertexCollectionKey, VPackValue(_vertexCollection));
-  b.add(Utils::edgeCollectionKey, VPackValue(_edgeCollection));
-  b.add(Utils::globalSuperstepKey, VPackValue(0));
-  b.add(Utils::algorithmKey, VPackValue(_algorithm));
-  b.close();
-  
-  sendToAllShards(Utils::nextGSSPath, b.slice());
+  std::vector<ClusterCommRequest> requests;
+  for (auto const &it : vertexServerMap) {
+    VPackBuilder b;
+    b.openObject();
+    b.add(Utils::executionNumberKey, VPackValue(_executionNumber));
+    b.add(Utils::coordinatorIdKey, VPackValue(coordinatorId));
+    b.add(Utils::vertexCollectionKey, VPackValue(_vertexCollection->name()));
+    b.add(Utils::vertexShardsListKey, VPackValue(VPackValueType::Array));
+    for (ShardID const &vit : it.second) {
+      b.add(VPackValue(vit));
+    }
+    b.close();
+    b.add(Utils::edgeShardsListKey, VPackValue(VPackValueType::Array));
+    for (ShardID const &eit : edgeServerMap[it.first]) {
+      b.add(VPackValue(eit));
+    }
+    b.close();
+    //b.add(Utils::vertexCollectionKey, VPackValue(_vertexCollection));
+    //b.add(Utils::edgeCollectionKey, VPackValue(_edgeCollection));
+    b.add(Utils::globalSuperstepKey, VPackValue(0));
+    b.add(Utils::algorithmKey, VPackValue(_algorithm));
+    b.close();
+    
+    auto body = std::make_shared<std::string const>(b.toJson());
+    requests.emplace_back("server:" + it.first, rest::RequestType::POST, baseUrl+Utils::nextGSSPath, body);
+  }
+  size_t nrDone = 0;
+  cc->performRequests(requests, 120.0, nrDone, LogTopic("Pregel Conductor"));
+  LOG(INFO) << "Send messages to " << nrDone << " shards of " << _vertexCollection->name();
+  // look at results
+  printResults(requests);
 }
 
 void Conductor::finishedGlobalStep(VPackSlice &data) {
-  MUTEX_LOCKER(locker, writeMutex);
+  MUTEX_LOCKER(locker, _finishedGSSMutex);
 
   LOG(INFO) << "Conductor received finished callback";
   if (_state != ExecutionState::RUNNING) {
-    LOG(WARN) << "Conductor did not expect another finishedGlobalStep()";
+    LOG(WARN) << "Conductor did not expect another finishedGlobalStep call";
     return;
   }
   
   _responseCount++;
-  if (_responseCount >= _dbServerCount) {
+  VPackSlice isDone = data.get(Utils::doneKey);
+  if (isDone.isBool() && isDone.getBool()) {
+    _doneCount++;
+  }
+  
+  if (_responseCount == _dbServerCount) {
+    LOG(INFO) << "Finished gss " << _globalSuperstep;
     _globalSuperstep++;
     
-    if (_globalSuperstep >= 25) {
-      LOG(INFO) << "We did 25 rounds";
+    std::string baseUrl = Utils::baseUrl(_vocbaseGuard.vocbase());
+    if (_doneCount == _dbServerCount ||  _globalSuperstep >= 25) {
+      LOG(INFO) << "Done. We did " << _globalSuperstep << " rounds";
       VPackBuilder b;
       b.openObject();
       b.add(Utils::executionNumberKey, VPackValue(_executionNumber));
       b.add(Utils::globalSuperstepKey, VPackValue(_globalSuperstep));
       b.close();
-      sendToAllShards(Utils::writeResultsPath, b.slice());
+      sendToAllShards(baseUrl+Utils::writeResultsPath, b.slice());
       _state = ExecutionState::FINISHED;
-    } else {
+      
+    } else {// trigger next superstep
       VPackBuilder b;
       b.openObject();
       b.add(Utils::executionNumberKey, VPackValue(_executionNumber));
       b.add(Utils::globalSuperstepKey, VPackValue(_globalSuperstep));
       b.close();
-      sendToAllShards(Utils::nextGSSPath, b.slice());
-      LOG(INFO) << "Conductor started new gss\n";
+      sendToAllShards(baseUrl+Utils::nextGSSPath, b.slice());
+      LOG(INFO) << "Conductor started new gss " << _globalSuperstep;
     }
   }
 }
@@ -115,33 +164,50 @@ void Conductor::cancel() {
 }
 
 int Conductor::sendToAllShards(std::string path, VPackSlice const& config) {
-  
-  ClusterInfo* ci = ClusterInfo::instance();
   ClusterComm* cc = ClusterComm::instance();
-  //CoordTransactionID coordTransactionID = TRI_NewTickServer();
+  std::unordered_map<ServerID, std::vector<ShardID>> vertexServerMap, edgeServerMap;
+  resolveWorkerServers(vertexServerMap, edgeServerMap);
   
-  
-  
-  shared_ptr<vector<ShardID>> shardIDs = ci->getShardList(_vertexCollectionID);// ->getCurrentDBServers();
-  _dbServerCount = shardIDs->size();
+  _dbServerCount = vertexServerMap.size();
   _responseCount = 0;
+  _doneCount = 0;
   
-  if (shardIDs->size() == 0) {
-    LOG(WARN) << "No shards registered for " << _vertexCollection;
+  if (_dbServerCount == 0) {
+    LOG(WARN) << "No shards registered for " << _vertexCollection->name();
     return TRI_ERROR_FAILED;
   }
   
   auto body = std::make_shared<std::string const>(config.toJson());
-  vector<ClusterCommRequest> requests;
-  for (auto it = shardIDs->begin(); it != shardIDs->end(); ++it) {
-    requests.emplace_back("shard:" + *it, rest::RequestType::POST, path, body);
+  std::vector<ClusterCommRequest> requests;
+  for (auto const &it : vertexServerMap) {
+    requests.emplace_back("server:" + it.first, rest::RequestType::POST, path, body);
   }
-  
-  LOG(INFO) << "Constructed requests";
 
   size_t nrDone = 0;
   cc->performRequests(requests, 120.0, nrDone, LogTopic("Pregel Conductor"));
-  LOG(INFO) << "Send messages to " << nrDone << " shards of " << _vertexCollection;
-
+  LOG(INFO) << "Send messages to " << nrDone << " shards of " << _vertexCollection->name();
+  printResults(requests);
+  
   return TRI_ERROR_NO_ERROR;
 }
+
+void Conductor::resolveWorkerServers(std::unordered_map<ServerID, std::vector<ShardID>> &vertexServerMap,
+                                     std::unordered_map<ServerID, std::vector<ShardID>> &edgeServerMap) {
+  ClusterInfo* ci = ClusterInfo::instance();
+  std::shared_ptr<std::vector<ShardID>> vertexShardIDs = ci->getShardList(_vertexCollection->cid_as_string());
+  std::shared_ptr<std::vector<ShardID>> edgeShardIDs = ci->getShardList(_edgeCollection->cid_as_string());
+  
+  for (auto const &shard : *vertexShardIDs) {
+    std::shared_ptr<std::vector<ServerID>> servers = ci->getResponsibleServer(shard);
+    if (servers->size() > 0) {
+      vertexServerMap[(*servers)[0]].push_back(shard);
+    }
+  }
+  for (auto const &shard : *edgeShardIDs) {
+    std::shared_ptr<std::vector<ServerID>> servers = ci->getResponsibleServer(shard);
+    if (servers->size() > 0) {
+      edgeServerMap[(*servers)[0]].push_back(shard);
+    }
+  }
+}
+
diff --git a/arangod/Pregel/Conductor.h b/arangod/Pregel/Conductor.h
index 4c627c1230..552fe13136 100755
--- a/arangod/Pregel/Conductor.h
+++ b/arangod/Pregel/Conductor.h
@@ -40,11 +40,10 @@ namespace pregel {
   class Conductor {
   public:
     
-    Conductor(int32_t executionNumber,
-              //TRI_vocbase_t *vocbase,
-              std::string const&vertexCollection,
-              CollectionID vertexCollectionID,
-              std::string const& edgeCollection,
+    Conductor(unsigned int executionNumber,
+              TRI_vocbase_t *vocbase,
+              std::shared_ptr<LogicalCollection> vertexCollection,
+              std::shared_ptr<LogicalCollection> edgeCollection,
               std::string const& algorithm);
     
     void start();
@@ -54,20 +53,24 @@ namespace pregel {
     ExecutionState getState() {return _state;}
     
   private:
-    Mutex writeMutex;// prevents concurrent calls to finishedGlobalStep
-    
-    int _executionNumber;
-    int _globalSuperstep;
+    Mutex _finishedGSSMutex;// prevents concurrent calls to finishedGlobalStep
+    VocbaseGuard _vocbaseGuard;
+    const unsigned int _executionNumber;
+      
+    unsigned int _globalSuperstep;
     int32_t _dbServerCount = 0;
     int32_t _responseCount = 0;
-    
-    //TRI_vocbase_t *_vocbase;
-    std::string _vertexCollection, _edgeCollection;
+    int32_t _doneCount = 0;
+      
+    std::shared_ptr<LogicalCollection> _vertexCollection, _edgeCollection;
     CollectionID _vertexCollectionID;
     std::string _algorithm;
     
     ExecutionState _state = ExecutionState::RUNNING;
+      
     // convenience
+      void resolveWorkerServers(std::unordered_map<ServerID, std::vector<ShardID>> &vertexServerMap,
+                                std::unordered_map<ServerID, std::vector<ShardID>> &edgeServerMap);
     int sendToAllShards(std::string url, VPackSlice const& body);
   };
 }
diff --git a/arangod/Pregel/InMessageCache.cpp b/arangod/Pregel/InMessageCache.cpp
index 18c5ba291f..55b25d869f 100755
--- a/arangod/Pregel/InMessageCache.cpp
+++ b/arangod/Pregel/InMessageCache.cpp
@@ -25,6 +25,7 @@
 
 #include "Basics/MutexLocker.h"
 #include "Basics/StaticStrings.h"
+#include "Basics/VelocyPackHelper.h"
 
 #include <velocypack/Iterator.h>
 #include <velocypack/velocypack-aliases.h>
@@ -87,9 +88,11 @@ void InMessageCache::addMessages(VPackArrayIterator incomingMessages) {
   }
 }
 
-VPackArrayIterator InMessageCache::getMessages(std::string const& vertexId) {
+VPackSlice InMessageCache::getMessages(std::string const& vertexId) {
   LOG(INFO) << "Querying messages from in queue\n";
   auto vmsg = _messages.find(vertexId);
-  if (vmsg != _messages.end()) return VPackArrayIterator(vmsg->second->slice());
-  else return VPackArrayIterator(VPackSlice());
+  if (vmsg != _messages.end()) {
+    return vmsg->second->slice();
+  }
+  else return VPackSlice();
 }
diff --git a/arangod/Pregel/InMessageCache.h b/arangod/Pregel/InMessageCache.h
index 650705627a..ee421e26a5 100755
--- a/arangod/Pregel/InMessageCache.h
+++ b/arangod/Pregel/InMessageCache.h
@@ -45,7 +45,7 @@ public:
   ~InMessageCache();
   
   void addMessages(VPackArrayIterator messages);
-  arangodb::velocypack::ArrayIterator getMessages(ShardID const& shardId);
+  VPackSlice getMessages(ShardID const& shardId);
   void clean();
   
 private:
diff --git a/arangod/Pregel/OutMessageCache.cpp b/arangod/Pregel/OutMessageCache.cpp
index 692494c4f3..56f8565c85 100755
--- a/arangod/Pregel/OutMessageCache.cpp
+++ b/arangod/Pregel/OutMessageCache.cpp
@@ -32,7 +32,7 @@
 using namespace arangodb;
 using namespace arangodb::pregel;
 
-OutMessageCache::OutMessageCache(CollectionID &vertexCollection) : _collection(vertexCollection) {
+OutMessageCache::OutMessageCache(CollectionID &vertexCollection, std::string baseUrl) : _collection(vertexCollection) {
   _ci = ClusterInfo::instance();
   
   auto shardMap = _ci->getShardList(vertexCollection);
@@ -72,10 +72,10 @@ void OutMessageCache::addMessage(std::string key, VPackSlice slice) {
   int res = _ci->getResponsibleShard(_collection, keyDoc.slice(), true,
                                      responsibleShard, usesDefaultShardingAttributes);
   if (res != TRI_ERROR_NO_ERROR) {
-    THROW_ARANGO_EXCEPTION(res);
+    THROW_ARANGO_EXCEPTION_MESSAGE(res, "OutMessageCache could not resolve the responsible shard");
   }
   TRI_ASSERT(usesDefaultShardingAttributes);// should be true anyway
-  
+    
   //std::unordered_map<std::string, VPackBuilder*> vertexMap =;
   auto it = _map[responsibleShard].find(key);
   if (it != _map[responsibleShard].end()) {// more than one message
@@ -96,54 +96,17 @@ void OutMessageCache::addMessage(std::string key, VPackSlice slice) {
     b.release();
   }
 }
-/*
-void OutMessageCache::addMessages(VPackArrayIterator incomingMessages) {
-  
-  //unordered_map<string, vector<VPackSlice>> messageBucket;
-  //VPackSlice messages = data.get(Utils::messagesKey);
-  for (auto const &it : incomingMessages) {
-    std::string vertexId = it.get(StaticStrings::ToString).copyString();
-    
-    auto vmsg = _messages.find(vertexId);
-    if (vmsg != _messages.end()) {
-      
-      // if no combiner
-      // vmsg->add(it.slice())
-      
-      // TODO do not hardcode combiner
-      int64_t old = vmsg->second->slice().get("value").getInt();
-      int64_t nw = it.get("value").getInt();
-      if (nw < old) {
-        vmsg->second->clear();
-        vmsg->second->add(it);
-      }
-    } else {
-      // assuming we have a combiner
-      std::unique_ptr<VPackBuilder> b(new VPackBuilder());
-      b->add(it);
-      _messages[vertexId] = b.get();
-      b.release();
-      
-      // if no combiner
-      // VPackBuilder *arr = new VPackBuilder(it);
-      // arr->openArray();
-      // arr->add(it)
-      // _messages[vertexId] = arr;
-    }
-  }
-}*/
 
 void OutMessageCache::getMessages(ShardID const& shardId, VPackBuilder &outBuilder) {
   auto shardIt = _map.find(shardId);
+  outBuilder.openArray();
   if (shardIt != _map.end()) {
     //auto vertices = *shardIt;
-    outBuilder.openArray();
     for (auto messagesPair : shardIt->second) {
       outBuilder.add(VPackArrayIterator(messagesPair.second->slice()));      
     }
-    outBuilder.close();
     //return ArrayIterator(vmsg->second->slice())
-  
   }
+  outBuilder.close();
   //else return VPackSlice();
 }
diff --git a/arangod/Pregel/OutMessageCache.h b/arangod/Pregel/OutMessageCache.h
index 87c0f59657..f4a59b801a 100755
--- a/arangod/Pregel/OutMessageCache.h
+++ b/arangod/Pregel/OutMessageCache.h
@@ -40,19 +40,23 @@ namespace pregel {
  processing */
 class OutMessageCache {
 public:
-  OutMessageCache(CollectionID &vertexCollection);
+  OutMessageCache(CollectionID &vertexCollection, std::string baseUrl);
   ~OutMessageCache();
   
   void addMessage(std::string key, VPackSlice slice);
   //void addMessages(VPackArrayIterator messages);
   void getMessages(ShardID const& shardId, VPackBuilder &outBuilder);
+    
+    void sendMessages();
   void clean();
+
   
 private:
   // two stage map: shard -> vertice -> message
   std::unordered_map<std::string, std::unordered_map<std::string, VPackBuilder*>> _map;
   ClusterInfo *_ci;
   CollectionID _collection;
+  size_t _numVertices;
 };
 
 }}
diff --git a/arangod/Pregel/Utils.cpp b/arangod/Pregel/Utils.cpp
index 1bb13f5298..132152b823 100755
--- a/arangod/Pregel/Utils.cpp
+++ b/arangod/Pregel/Utils.cpp
@@ -21,20 +21,31 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 #include "Utils.h"
+#include "Basics/StringUtils.h"
+#include "VocBase/vocbase.h"
 
 using namespace arangodb::pregel;
 
-std::string const Utils::nextGSSPath = "/_api/pregel/nextGSS";
-std::string const Utils::finishedGSSPath = "/_api/pregel/finishedGSS";
-std::string const Utils::messagesPath = "/_api/pregel/messages";
-std::string const Utils::writeResultsPath = "/_api/pregel/writeResults";
+std::string const Utils::apiPrefix = "/_api/pregel/";
+
+
+std::string const Utils::nextGSSPath = "nextGSS";
+std::string const Utils::finishedGSSPath = "finishedGSS";
+std::string const Utils::messagesPath = "messages";
+std::string const Utils::writeResultsPath = "writeResults";
 
 std::string const Utils::executionNumberKey = "extn";
-std::string const Utils::vertexCollectionKey = "vxcln";
-std::string const Utils::edgeCollectionKey = "ecnln";
+std::string const Utils::vertexCollectionKey = "vertexCollection";
+std::string const Utils::vertexShardsListKey = "vertexShards";
+std::string const Utils::edgeShardsListKey = "edgeShards";
+std::string const Utils::resultShardKey = "resultShard";
 std::string const Utils::coordinatorIdKey = "coordinatorId";
 std::string const Utils::algorithmKey = "algorithm";
 std::string const Utils::globalSuperstepKey = "gss";
 std::string const Utils::messagesKey = "msgs";
 std::string const Utils::senderKey = "sender";
 std::string const Utils::doneKey = "done";
+
+std::string Utils::baseUrl(TRI_vocbase_t *vocbase) {
+  return  "/_db/" + basics::StringUtils::urlEncode(vocbase->name()) + Utils::apiPrefix;
+}
diff --git a/arangod/Pregel/Utils.h b/arangod/Pregel/Utils.h
index c737dc70c0..0f2a30598f 100755
--- a/arangod/Pregel/Utils.h
+++ b/arangod/Pregel/Utils.h
@@ -25,13 +25,19 @@
 
 #include "Basics/Common.h"
 
+
+struct TRI_vocbase_t;
 namespace arangodb {
+    
 namespace pregel {
+    
   class Utils {
     Utils() = delete;
     
   public:
     // constants
+    static std::string const apiPrefix;
+      
     static std::string const nextGSSPath;
     static std::string const finishedGSSPath;
     static std::string const messagesPath;
@@ -39,7 +45,9 @@ namespace pregel {
     
     static std::string const executionNumberKey;
     static std::string const vertexCollectionKey;
-    static std::string const edgeCollectionKey;
+    static std::string const vertexShardsListKey;
+    static std::string const edgeShardsListKey;
+    static std::string const resultShardKey;
     static std::string const algorithmKey;
     static std::string const coordinatorIdKey;
     
@@ -47,6 +55,8 @@ namespace pregel {
     static std::string const messagesKey;
     static std::string const senderKey;
     static std::string const doneKey;
+      
+      static std::string baseUrl(TRI_vocbase_t *vocbase);
 
   };
 }
diff --git a/arangod/Pregel/Vertex.cpp b/arangod/Pregel/Vertex.cpp
index 589457ca6e..51bd79519d 100755
--- a/arangod/Pregel/Vertex.cpp
+++ b/arangod/Pregel/Vertex.cpp
@@ -32,35 +32,39 @@ using namespace arangodb;
 using namespace arangodb::velocypack;
 using namespace arangodb::pregel;
 
-Vertex::Vertex(VPackSlice document)  {
-  documentId = document.get(StaticStrings::IdString).copyString();
+Message::Message(VPackSlice slice) {
+  VPackSlice s = slice.get("value");
+  _value = s.getSmallInt() || s.getInt() ? s.getInt() : -1;
+}
+
+Vertex::Vertex(VPackSlice document) : _data(document)  {
+  //documentId = document.get(StaticStrings::IdString).copyString();
   VPackSlice s = document.get("value");
-  _vertexState = s.getSmallInt() || s.getInt() ? s.getInt() : -1;
+  _vertexState = s.isInteger() ? s.getInt() : -1;
 }
 
 Vertex::~Vertex() {
-  for (auto const &it : _edges) {
+  /*for (auto const &it : _edges) {
     delete(it);
-  }
+  }*/
   _edges.clear();
 }
 
-void Vertex::compute(int gss, VPackArrayIterator const &messages, OutMessageCache* const cache) {
-  
+void Vertex::compute(int gss, MessageIterator const &messages, OutMessageCache* const cache) {
   int current = _vertexState;
   for (auto const &msg : messages) {
-    int val = msg.getInt();
-    if (val < current) current = val;
+    if (msg._value < current) current = msg._value;
   }
   if (current >= 0 && (gss == 0 || current != _vertexState))  {
     _vertexState = current;
     for (auto const &edge : _edges) {
+      VPackSlice toID = edge._data.get(StaticStrings::ToString);
       VPackBuilder b;
       b.openObject();
-      b.add(StaticStrings::ToString, VPackValue(edge->toId));
-      b.add("val", VPackValue(edge->value + current));
+      b.add(StaticStrings::ToString, toID);
+      b.add("value", VPackValue(edge._value + current));
       b.close();
-      cache->addMessage(edge->toId, b.slice());
+      cache->addMessage(toID.copyString(), b.slice());
     }
   } else voteHalt();
 }
diff --git a/arangod/Pregel/Vertex.h b/arangod/Pregel/Vertex.h
index 964b0ce91f..f736bdc5df 100755
--- a/arangod/Pregel/Vertex.h
+++ b/arangod/Pregel/Vertex.h
@@ -36,40 +36,108 @@ namespace pregel {
   };
   
   class OutMessageCache;
+    
+    struct Message {
+        Message(VPackSlice slice);
+        
+        int _value; // demo
+    };
+    
+  //template <typename T>
+  class MessageIterator {
+  public:
+      MessageIterator() = delete;
+      
+      typedef MessageIterator iterator;
+      typedef const MessageIterator const_iterator;
+      
+      explicit MessageIterator(VPackSlice slice) : _slice(slice) {
+          if (_slice.isNull() || _slice.isNone()) _size = 0;
+          else if (_slice.isArray()) _size = _slice.length();
+          else _size = 1;
+      }
+      
+      iterator begin() {
+          return MessageIterator(_slice);
+      }
+      const_iterator begin() const {
+          return MessageIterator(_slice);
+      }
+      iterator end() {
+          auto it = MessageIterator(_slice);
+          it._position = it._size;
+          return it;
+      }
+      const_iterator end() const {
+          auto it = MessageIterator(_slice);
+          it._position = it._size;
+          return it;
+      }
+      Message operator*() const {
+          if (_slice.isArray()) {
+              return Message(_slice.at(_position));
+          } else {
+              return Message(_slice);
+          }
+      }
+      
+      // prefix ++
+      MessageIterator& operator++() {
+          ++_position;
+          return *this;
+      }
+      
+      // postfix ++
+      MessageIterator operator++(int) {
+          MessageIterator result(*this);
+          ++(*this);
+          return result;
+      }
+      
+      bool operator!=(MessageIterator const& other) const {
+          return _position != other._position;
+      }
+      
+      size_t size() const {
+          return _size;
+      }
+      
+  private:
+      VPackSlice _slice;
+      size_t _position = 0;
+      size_t _size = 1;
+  };
   
   struct Edge {
-  public:
-    std::string edgeId;
-    std::string toId;
-    
-    int value;// demo
+    Edge(VPackSlice data) : _data(data) {}
+    VPackSlice _data;
+      
+    //protected: virtual void loadData() = 0;
+      
+    int _value;// demo
   };
   
   class Vertex {
     friend class Worker;
+    friend class WorkerJob;
+
   public:
     //typedef std::iterator<std::forward_iterator_tag, VPackSlice> MessageIterator;
     Vertex(VPackSlice document);
     ~Vertex();
-    void compute(int gss, VPackArrayIterator const &messages, OutMessageCache* const cache);
+    void compute(int gss, MessageIterator const &messages, OutMessageCache* const cache);
     
     VertexActivationState state() {return _activationState;}
-    //std::vector<VPackSlice> messages() {return _messages;}
-    
-    std::vector<Edge*> _edges;
-    std::string documentId;
+    std::vector<Edge> _edges;
 
   protected:
     void voteHalt() {_activationState = VertexActivationState::STOPPED;}
-    //void sendMessage(VPackBuilder &message) {_messages.push_back(message.slice());}
+    int _vertexState;// demo
+    VPackSlice _data;
 
   private:
     VertexActivationState _activationState;
-    //std::vector<VPackSlice> _messages;
-    
-    int _vertexState;// demo
   };
-
 }
 }
 #endif
diff --git a/arangod/Pregel/Worker.cpp b/arangod/Pregel/Worker.cpp
index bc57cda117..d943ed1bcd 100755
--- a/arangod/Pregel/Worker.cpp
+++ b/arangod/Pregel/Worker.cpp
@@ -26,15 +26,21 @@
 #include "InMessageCache.h"
 #include "OutMessageCache.h"
 
+#include "Basics/MutexLocker.h"
 #include "Cluster/ClusterInfo.h"
 #include "Cluster/ClusterComm.h"
 #include "VocBase/ticks.h"
 #include "VocBase/vocbase.h"
+#include "VocBase/LogicalCollection.h"
+#include "VocBase/EdgeCollectionInfo.h"
+
 #include "Indexes/Index.h"
 #include "Dispatcher/DispatcherQueue.h"
 #include "Dispatcher/DispatcherFeature.h"
+#include "Utils/Transaction.h"
 #include "Utils/SingleCollectionTransaction.h"
 #include "Utils/StandaloneTransactionContext.h"
+#include "Utils/OperationCursor.h"
 #include "Indexes/EdgeIndex.h"
 
 #include <velocypack/Iterator.h>
@@ -45,113 +51,121 @@
 using namespace arangodb;
 using namespace arangodb::pregel;
 
-Worker::Worker(int executionNumber,
+Worker::Worker(unsigned int executionNumber,
                TRI_vocbase_t *vocbase,
-               VPackSlice s) : _vocbaseGuard(vocbase), _executionNumber(executionNumber) {
+               VPackSlice s) : _vocbase(vocbase), _executionNumber(executionNumber) {
 
   //VPackSlice algo = s.get("algo");
-  _vertexCollection = s.get(Utils::vertexCollectionKey).copyString();
-  _edgeCollection = s.get(Utils::edgeCollectionKey).copyString();
-  LOG(INFO) << "starting worker with (" << _vertexCollection << ", " << _edgeCollection << ")";
+  
+  VPackSlice coordID = s.get(Utils::coordinatorIdKey);
+  VPackSlice vertexShardIDs = s.get(Utils::vertexShardsListKey);
+  VPackSlice edgeShardIDs = s.get(Utils::edgeShardsListKey);
+  // TODO support more shards
+  if (!(coordID.isString() && vertexShardIDs.length() == 1 && edgeShardIDs.length() == 1)) {
+    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_BAD_PARAMETER, "Only one shard per collection supported");
+  }
+  _coordinatorId = coordID.copyString();
+  _vertexCollectionName = s.get(Utils::vertexCollectionKey).copyString();// readable name of collection
+  _vertexShardID = vertexShardIDs.at(0).copyString();
+  _edgeShardID = edgeShardIDs.at(0).copyString();
+  LOG(INFO) << "Received collection " << _vertexCollectionName;
+  LOG(INFO) << "starting worker with (" << _vertexShardID << ", " << _edgeShardID << ")";
   
   _cache1 = new InMessageCache();
   _cache2 = new InMessageCache();
   _currentCache = _cache1;
   
-  SingleCollectionTransaction trx(StandaloneTransactionContext::Create(vocbase),
-                                  _vertexCollection, TRI_TRANSACTION_READ);
-  int res = trx.begin();
-  
+  SingleCollectionTransaction *trx = new SingleCollectionTransaction(StandaloneTransactionContext::Create(_vocbase),
+                                  _vertexShardID, TRI_TRANSACTION_READ);
+  int res = trx->begin();
   if (res != TRI_ERROR_NO_ERROR) {
     THROW_ARANGO_EXCEPTION_FORMAT(res, "while looking up vertices '%s'",
-                                  _vertexCollection.c_str());
+                                  _vertexShardID.c_str());
     return;
   }
+  // resolve planId
+  _vertexCollectionPlanId = trx->documentCollection()->planId_as_string();
   
-  OperationResult result = trx.all(_vertexCollection, 0, UINT64_MAX, OperationOptions());
+  OperationResult result = trx->all(_vertexShardID, 0, UINT64_MAX, OperationOptions());
   // Commit or abort.
-  res = trx.finish(result.code);
-  
+  res = trx->finish(result.code);
   if (!result.successful()) {
-    THROW_ARANGO_EXCEPTION_FORMAT(result.code, "while looking up graph '%s'",
-                                  _vertexCollection.c_str());
+    THROW_ARANGO_EXCEPTION_FORMAT(result.code, "while looking up graph '%s'", _vertexCollectionName.c_str());
   }
   if (res != TRI_ERROR_NO_ERROR) {
-    THROW_ARANGO_EXCEPTION_FORMAT(res, "while looking up graph '%s'",
-                                  _vertexCollection.c_str());
+    THROW_ARANGO_EXCEPTION_FORMAT(res, "while looking up graph '%s'", _vertexCollectionName.c_str());
   }
   VPackSlice vertices = result.slice();
   if (vertices.isExternal()) {
     vertices = vertices.resolveExternal();
   }
+  _transactions.push_back(trx);// store transactions, otherwise VPackSlices become invalid
   
-  SingleCollectionTransaction trx2(StandaloneTransactionContext::Create(vocbase),
-                                  _edgeCollection, TRI_TRANSACTION_READ);
-  res = trx2.begin();
+  // ======= Look up edges
   
+  trx = new SingleCollectionTransaction(StandaloneTransactionContext::Create(_vocbase),
+                                        _edgeShardID, TRI_TRANSACTION_READ);
+  res = trx->begin();
   if (res != TRI_ERROR_NO_ERROR) {
-    THROW_ARANGO_EXCEPTION_FORMAT(res, "while looking up edges '%s'",
-                                  _vertexCollection.c_str());
-    return;
+    THROW_ARANGO_EXCEPTION_FORMAT(res, "while looking up edges '%s'", _edgeShardID.c_str());
   }
+  _transactions.push_back(trx);
   
-  /*OperationResult result2 = trx2.all(edgeCollection, 0, UINT64_MAX, OperationOptions());
-  // Commit or abort.
-  res = trx.finish(result.code);
+  auto info = std::make_unique<arangodb::traverser::EdgeCollectionInfo>(trx, _edgeShardID, TRI_EDGE_OUT,
+                                                                        StaticStrings::FromString, 0);
   
-  if (!result2.successful() || res != TRI_ERROR_NO_ERROR) {
-    THROW_ARANGO_EXCEPTION_FORMAT(result2.code, "while looking up graph '%s'",
-                                  edgeCollection.c_str());
-  }
-  VPackSlice edges = result.slice();
-  if (edges.isExternal()) {
-    edges = vertices.resolveExternal();
-  }*/
-  
-  SingleCollectionTransaction::IndexHandle handle = trx2.edgeIndexHandle(_edgeCollection);
-  if (handle.isEdgeIndex()) {
-    THROW_ARANGO_EXCEPTION(TRI_ERROR_BAD_PARAMETER);
-  }
-  
-  std::shared_ptr<Index> edgeIndexPtr = handle.getIndex();
-  EdgeIndex* edgeIndex = static_cast<EdgeIndex*>(edgeIndexPtr.get());
-  
-  
-  /*map<std::string, vector<Edge*>> sortBucket;// TODO hash_map ?
-  for (auto const& it : velocypack::ArrayIterator(edges)) {
-    Edge *e = new Edge();
-    e->edgeId = it.get(StaticStrings::IdString).copyString();
-    e->toId = it.get(StaticStrings::ToString).copyString();
-    e->value = it.get("value").getInt();
-    sortBucket[e->toId].push_back(e);
-  }*/
+  size_t edgeCount = 0;
   VPackArrayIterator arr = VPackArrayIterator(vertices);
   LOG(INFO) << "Found vertices: " << arr.size();
-  for (auto const &it : arr) {
-    Vertex *v = new Vertex(it);
-    _vertices[v->documentId] = v;
-    
-    //v._edges = sortBucket[v.documentId];
-    
-    TransactionBuilderLeaser b(&trx2);
-    b->openArray();
-    b->add(it.get(StaticStrings::IdString));
-    b->add(VPackValue(VPackValueType::Null));
-    b->close();
-    IndexIterator* vit = edgeIndex->iteratorForSlice(&trx2, nullptr, b->slice(), false);
-    TRI_doc_mptr_t *edgePack;
-    while((edgePack = vit->next()) != nullptr) {
-      VPackSlice s(edgePack->vpack());
-      
-      std::unique_ptr<Edge> e(new Edge());
-      e->edgeId = it.get(StaticStrings::IdString).copyString();
-      e->toId = it.get(StaticStrings::ToString).copyString();
-      VPackSlice i = it.get("value");
-      e->value = i.isSmallInt() || i.isInt() ? i.getInt() : 1;
-      v->_edges.push_back(e.get());
-      e.release();
+  for (auto it : arr) {
+    LOG(INFO) << it.toJson();
+    if (it.isExternal()) {
+      it = it.resolveExternal();
     }
+    
+    std::string vertexId = it.get(StaticStrings::KeyString).copyString();
+    std::unique_ptr<Vertex> v (new Vertex(it));
+    _vertices[vertexId] = v.get();
+    
+    std::string key = _vertexCollectionName+"/"+vertexId;// TODO geht das schneller
+    LOG(INFO) << "Retrieving edge " << key;
+    
+    auto cursor = info->getEdges(key);
+    if (cursor->failed()) {
+      THROW_ARANGO_EXCEPTION_FORMAT(cursor->code, "while looking up edges '%s' from %s",
+                                    key.c_str(), _edgeShardID.c_str());
+    }
+    
+    std::vector<TRI_doc_mptr_t*> result;
+    result.reserve(1000);
+    while (cursor->hasMore()) {
+      cursor->getMoreMptr(result, 1000);
+      for (auto const& mptr : result) {
+        
+        VPackSlice s(mptr->vpack());
+        if (s.isExternal()) {
+          s = s.resolveExternal();
+        }
+        LOG(INFO) << s.toJson();
+        
+        VPackSlice i = s.get("value");
+        v->_edges.emplace_back(s);
+        v->_edges.end()->_value = i.isInteger() ? i.getInt() : 1;
+        edgeCount++;
+        
+      }
+    }
+    LOG(INFO) << "done retrieving edge";
+    
+    v.release();
   }
+  trx->finish(res);
+  if (res != TRI_ERROR_NO_ERROR) {
+    THROW_ARANGO_EXCEPTION_FORMAT(res, "after looking up edges '%s'", _edgeShardID.c_str());
+  }
+  
+  LOG(INFO) << "Resolved " << _vertices.size() << " vertices";
+  LOG(INFO) << "Resolved " << edgeCount << " edges";
 }
 
 Worker::~Worker() {
@@ -159,33 +173,38 @@ Worker::~Worker() {
     delete(it.second);
   }
   _vertices.clear();
+  for (auto const &it : _transactions) {// clean transactions
+    delete(it);
+  }
+  _transactions.clear();
 }
 
 void Worker::nextGlobalStep(VPackSlice data) {
+  LOG(INFO) << "Called next global step: " << data.toString();
+  
   // TODO do some work?
   VPackSlice gssSlice = data.get(Utils::globalSuperstepKey);
-  if (!gssSlice.isInt()) {
-    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_BAD_PARAMETER, "Invalid gss in body");
-  }
-  
-  int64_t gss = gssSlice.getInt();
-  if (gss == 0) {
-    VPackSlice cid = data.get(Utils::coordinatorIdKey);
-    //VPackSlice algo = data.get(Utils::algorithmKey);
-    if (cid.isString())
-      _coordinatorId = cid.copyString();
+  if (!gssSlice.isInteger()) {
+    THROW_ARANGO_EXCEPTION_FORMAT(TRI_ERROR_BAD_PARAMETER,
+                                  "Invalid gss in %s:%d", __FILE__, __LINE__);
   }
+  uint64_t gss = gssSlice.getUInt();
   _globalSuperstep = gss;
   InMessageCache *inCache = _currentCache;
-  if (_currentCache == _cache1) _currentCache = _cache2;
-  else _currentCache = _cache1;
+  if (_currentCache == _cache1) {
+    _currentCache = _cache2;
+  } else {
+    _currentCache = _cache1;
+  }
   
   std::unique_ptr<rest::Job> job(new WorkerJob(this, inCache));
   DispatcherFeature::DISPATCHER->addJob(job, false);
-  LOG(INFO) << "Worker started new gss computation\n";
+  LOG(INFO) << "Worker started new gss computation: " << gss;
 }
 
 void Worker::receivedMessages(VPackSlice data) {
+  MUTEX_LOCKER(locker, _messagesMutex);
+  
   VPackSlice gssSlice = data.get(Utils::globalSuperstepKey);
   VPackSlice messageSlice = data.get(Utils::messagesKey);
   if (!gssSlice.isInt() || !messageSlice.isArray()) {
@@ -202,47 +221,53 @@ void Worker::receivedMessages(VPackSlice data) {
 
 void Worker::writeResults() {
   
-  SingleCollectionTransaction trx(StandaloneTransactionContext::Create(_vocbaseGuard.vocbase()),
+  /*SingleCollectionTransaction trx(StandaloneTransactionContext::Create(_vocbaseGuard.vocbase()),
                                   _vertexCollection, TRI_TRANSACTION_WRITE);
   int res = trx.begin();
   
   if (res != TRI_ERROR_NO_ERROR) {
     LOG(ERR) << "cannot start transaction to load authentication";
     return;
-  }
+  }*/
 
   OperationResult result;
   OperationOptions options;
   options.waitForSync = false;
   options.mergeObjects = true;
   for (auto const &pair : _vertices) {
-    TransactionBuilderLeaser b(&trx);
-    b->openObject();
-    b->add(StaticStrings::KeyString, VPackValue(pair.second->documentId));
-    b->add("value", VPackValue(pair.second->_vertexState));
-    b->close();
-    result = trx.update(_vertexCollection, b->slice(), options);
+    //TransactionBuilderLeaser b(&trx);
+    VPackBuilder b;
+    b.openObject();
+    b.add(StaticStrings::KeyString, pair.second->_data.get(StaticStrings::KeyString));
+    b.add("value", VPackValue(pair.second->_vertexState));
+    b.close();
+    LOG(INFO) << b.toString();
+    /*result = trx.update(_vertexCollection, b->slice(), options);
     if (!result.successful()) {
       THROW_ARANGO_EXCEPTION_FORMAT(result.code, "while looking up graph '%s'",
                                     _vertexCollection.c_str());
-    }
+    }*/
   }
   // Commit or abort.
-  res = trx.finish(result.code);
+  /*res = trx.finish(result.code);
   
   if (res != TRI_ERROR_NO_ERROR) {
     THROW_ARANGO_EXCEPTION_FORMAT(res, "while looking up graph '%s'",
                                   _vertexCollection.c_str());
+  }*/
+}
+
+
+// ========== WorkerJob ==========
+
+static void waitForResults(std::vector<ClusterCommRequest> &requests) {
+  for (auto const& req : requests) {
+    auto& res = req.result;
+    if (res.status == CL_COMM_RECEIVED) {
+      LOG(INFO) << res.answer->payload().toJson();
+    }
   }
 }
-// ========== WorkerJob
-
-/*
-V8Job::~V8Job() {
-  if (_task != nullptr) {
-    V8PeriodicTask::jobDone(_task);
-  }
-}*/
 
 WorkerJob::WorkerJob(Worker *worker, InMessageCache *inCache) : Job("Pregel Job"), _worker(worker), _inCache(inCache) {
 }
@@ -252,10 +277,10 @@ void WorkerJob::work() {
     return;
   }
   LOG(INFO) << "Worker job started\n";
-  
-  OutMessageCache outCache(_worker->_vertexCollection);
-  
-  int64_t gss = _worker->_globalSuperstep;
+  // TODO cache this
+  OutMessageCache outCache(_worker->_vertexCollectionPlanId);
+
+  unsigned int gss = _worker->_globalSuperstep;
   bool isDone = true;
 
   if (gss == 0) {
@@ -263,62 +288,83 @@ void WorkerJob::work() {
     
     for (auto const &it : _worker->_vertices) {
       Vertex *v = it.second;
-      VPackArrayIterator messages = _inCache->getMessages(v->documentId);
-      v->compute(gss, messages, &outCache);
-      _worker->_activationMap[it.first] = v->state() == VertexActivationState::ACTIVE;
+      std::string key = v->_data.get(StaticStrings::KeyString).copyString();
+      
+      VPackSlice messages = _inCache->getMessages(key);
+      v->compute(gss, MessageIterator(messages), &outCache);
+      bool active = v->state() == VertexActivationState::ACTIVE;
+      if (!active) LOG(INFO) << "vertex has halted";
+      _worker->_activationMap[it.first] = active;
     }
   } else {
     for (auto &it : _worker->_activationMap) {
-      VPackArrayIterator messages = _inCache->getMessages(it.first);
-      if (messages.size() > 0 || it.second) {
+      VPackSlice messages = _inCache->getMessages(it.first);
+      MessageIterator iterator(messages);
+      if (iterator.size() > 0 || it.second) {
         isDone = false;
         
         Vertex *v = _worker->_vertices[it.first];
-        v->compute(gss, messages, &outCache);
+        v->compute(gss, iterator, &outCache);
         it.second = v->state() == VertexActivationState::ACTIVE;
       }
     }
   }
-  LOG(INFO) << "Worker job computations done, now distributing results\n";
+  LOG(INFO) << "Worker job computations done";
 
   if (_canceled) {
     return;
   }
   
-  // send messages to other shards
+  // ==================== send messages to other shards ====================
   ClusterComm *cc =  ClusterComm::instance();
   ClusterInfo *ci = ClusterInfo::instance();
+  std::string baseUrl = Utils::baseUrl(_worker->_vocbase);
   
   if (!isDone) {
-    std::shared_ptr<std::vector<ShardID>> shards = ci->getShardList(_worker->_vertexCollection);
+    LOG(INFO) << "Sending messages to shards";
+    std::shared_ptr<std::vector<ShardID>> shards = ci->getShardList(_worker->_vertexCollectionPlanId);
+    LOG(INFO) << "Seeing shards: " << shards->size();
+
     std::vector<ClusterCommRequest> requests;
-    for (auto it = shards->begin(); it != shards->end(); ++it) {
-      VPackBuilder package;
-      package.add(Utils::senderKey, VPackValue(ServerState::instance()->getId()));
-      package.add(Utils::executionNumberKey, VPackValue(_worker->_executionNumber));
-      package.add(Utils::globalSuperstepKey, VPackValue(gss+1));
-      VPackBuilder messages;
-      outCache.getMessages(*it, messages);
-      package.add(Utils::messagesKey, messages.slice());
-      package.close();
+    for (auto const &it : *shards) {
       
-      auto body = std::make_shared<std::string const>(package.toJson());
-      requests.emplace_back("shard:" + *it, rest::RequestType::POST, Utils::messagesPath, body);
+      VPackBuilder messages;
+      outCache.getMessages(it, messages);
+      if (_worker->_vertexShardID == it) {
+        LOG(INFO) << "Worker: Getting messages for myself";
+        _worker->_currentCache->addMessages(VPackArrayIterator(messages.slice()));
+      } else {
+        LOG(INFO) << "Worker: Sending messages for shard " << it;
+
+        VPackBuilder package;
+        package.openObject();
+        package.add(Utils::senderKey, VPackValue(ServerState::instance()->getId()));
+        package.add(Utils::executionNumberKey, VPackValue(_worker->_executionNumber));
+        package.add(Utils::globalSuperstepKey, VPackValue(gss+1));
+        package.add(Utils::messagesKey, messages.slice());
+        package.close();
+        // add a request
+        auto body = std::make_shared<std::string const>(package.toJson());
+        requests.emplace_back("shard:" + it, rest::RequestType::POST, baseUrl + Utils::messagesPath, body);
+      }
     }
     size_t nrDone = 0;
     cc->performRequests(requests, 120, nrDone, LogTopic("Pregel message transfer"));
+    waitForResults(requests);
   } else {
     LOG(INFO) << "Worker job has nothing more to process\n";
   }
   
   // notify the conductor that we are done.
   VPackBuilder package;
+  package.openObject();
   package.add(Utils::senderKey, VPackValue(ServerState::instance()->getId()));
   package.add(Utils::executionNumberKey, VPackValue(_worker->_executionNumber));
-  package.add(Utils::doneKey, VPackValue(isDone));
+  if (!isDone) package.add(Utils::doneKey, VPackValue(isDone));
   package.close();
   
-  // TODO handle communication failure
+  LOG(INFO) << "Sending finishedGSS to coordinator: " << _worker->_coordinatorId;
+  // TODO handle communication failures?
   CoordTransactionID coordinatorTransactionID = TRI_NewTickServer();
   auto headers =
   std::make_unique<std::unordered_map<std::string, std::string>>();
@@ -326,10 +372,10 @@ void WorkerJob::work() {
   cc->asyncRequest("", coordinatorTransactionID,
                    "server:"+_worker->_coordinatorId,
                    rest::RequestType::POST,
-                   Utils::finishedGSSPath,
+                   baseUrl + Utils::finishedGSSPath,
                    body, headers, nullptr, 90.0);
   
-  LOG(INFO) << "Worker job finished sending results\n";
+  LOG(INFO) << "Worker job finished sending stuff";
 }
 
 bool WorkerJob::cancel() {
diff --git a/arangod/Pregel/Worker.h b/arangod/Pregel/Worker.h
index 3c275ac5e3..e8512d259c 100755
--- a/arangod/Pregel/Worker.h
+++ b/arangod/Pregel/Worker.h
@@ -24,12 +24,14 @@
 #define ARANGODB_PREGEL_WORKER_H 1
 
 #include "Basics/Common.h"
+#include "Basics/Mutex.h"
 #include "VocBase/vocbase.h"
 #include "Scheduler/Task.h"
 #include "Cluster/ClusterInfo.h"
 #include "Dispatcher/Job.h"
 
 namespace arangodb {
+    class SingleCollectionTransaction;
 namespace pregel {
   class Vertex;
   class InMessageCache;
@@ -38,7 +40,7 @@ namespace pregel {
   class Worker {
     friend class WorkerJob;
   public:
-    Worker(int executionNumber, TRI_vocbase_t *vocbase, VPackSlice s);
+    Worker(unsigned int executionNumber, TRI_vocbase_t *vocbase, VPackSlice s);
     ~Worker();
       
     void nextGlobalStep(VPackSlice data);// called by coordinator
@@ -47,18 +49,21 @@ namespace pregel {
     
   private:
     /// @brief guard to make sure the database is not dropped while used by us
-    VocbaseGuard _vocbaseGuard;
-    
-    int _executionNumber;
-    int _globalSuperstep;
+    TRI_vocbase_t* _vocbase;
+    Mutex _messagesMutex;
+    const unsigned int _executionNumber;
+      
+    unsigned int _globalSuperstep;
     std::string _coordinatorId;
-    std::string _vertexCollection, _edgeCollection;
+    std::string _vertexCollectionName, _vertexCollectionPlanId;
+    ShardID _vertexShardID, _edgeShardID;
     
     std::unordered_map<std::string, Vertex*> _vertices;
     std::map<std::string, bool> _activationMap;
     
     InMessageCache *_cache1, *_cache2;
     InMessageCache *_currentCache;
+    std::vector<SingleCollectionTransaction*> _transactions;
   };
   
   class WorkerJob : public rest::Job {
diff --git a/arangod/RestHandler/RestPregelHandler.cpp b/arangod/RestHandler/RestPregelHandler.cpp
index b4d60544ec..6de026bd12 100644
--- a/arangod/RestHandler/RestPregelHandler.cpp
+++ b/arangod/RestHandler/RestPregelHandler.cpp
@@ -42,72 +42,76 @@ RestPregelHandler::RestPregelHandler(GeneralRequest* request, GeneralResponse* r
 : RestVocbaseBaseHandler(request, response) {}
 
 RestHandler::status RestPregelHandler::execute() {
-  LOG(INFO) << "Received request\n";
-  
-  bool parseSuccess = true;
-  std::shared_ptr<VPackBuilder> parsedBody =
-  parseVelocyPackBody(&VPackOptions::Defaults, parseSuccess);
-  VPackSlice body(parsedBody->start());// never nullptr
-  
-  if (!parseSuccess || !body.isObject()) {
-    LOG(ERR) << "Bad request body\n";
-    generateError(rest::ResponseCode::BAD,
-                  TRI_ERROR_NOT_IMPLEMENTED, "illegal request for /_api/pregel");
-  } else if (_request->requestType() == rest::RequestType::POST) {
+  try {    
+    bool parseSuccess = true;
+    std::shared_ptr<VPackBuilder> parsedBody =
+    parseVelocyPackBody(&VPackOptions::Defaults, parseSuccess);
+    VPackSlice body(parsedBody->start());// never nullptr
     
-    std::vector<std::string> const& suffix = _request->suffix();
-    VPackSlice sExecutionNum = body.get(Utils::executionNumberKey);
-    if (!sExecutionNum.isSmallInt() && !sExecutionNum.isInt()) {
-      LOG(ERR) << "Invalid execution number";
-      generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_HTTP_NOT_FOUND);
-      return status::DONE;
-    }
-    
-    int executionNumber = sExecutionNum.getInt();
+    if (!parseSuccess || !body.isObject()) {
+      LOG(ERR) << "Bad request body\n";
+      generateError(rest::ResponseCode::BAD,
+                    TRI_ERROR_NOT_IMPLEMENTED, "illegal request for /_api/pregel");
+    } else if (_request->requestType() == rest::RequestType::POST) {
+      
+      std::vector<std::string> const& suffix = _request->suffix();
+      VPackSlice sExecutionNum = body.get(Utils::executionNumberKey);
+      if (!sExecutionNum.isInteger()) {
+        LOG(ERR) << "Invalid execution number";
+        generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_HTTP_NOT_FOUND);
+        return status::DONE;
+      }
+      
+      unsigned int executionNumber = sExecutionNum.getUInt();
 
-    if (suffix.size() != 1) {
-      LOG(ERR) << "Invalid suffix";
-      generateError(rest::ResponseCode::NOT_FOUND,
-                    TRI_ERROR_HTTP_NOT_FOUND);
-      return status::DONE;
-    } else if (suffix[0] == "finishedGSS") {
-      LOG(INFO) << "finishedGSS";
-      Conductor *exe = JobMapping::instance()->conductor(executionNumber);
-      if (exe) {
-        exe->finishedGlobalStep(body);
-      } else {
-        LOG(ERR) << "Conductor not found\n";
-      }
-    } else if (suffix[0] == "nextGSS") {
-      LOG(INFO) << "nextGSS";
-      Worker *w = JobMapping::instance()->worker(executionNumber);
-      if (!w) {// can happen if gss == 0
-        LOG(INFO) << "creating worker";
-        w = new Worker(executionNumber, _vocbase, body);
-        JobMapping::instance()->addWorker(w, executionNumber);
-      }
-      w->nextGlobalStep(body);
-    } else if (suffix[0] == "messages") {
-      LOG(INFO) << "messages";
-      Worker *exe = JobMapping::instance()->worker(executionNumber);
-      if (exe) {
-        exe->receivedMessages(body);
-      }
-    } else if (suffix[0] == "writeResults") {
-      Worker *exe = JobMapping::instance()->worker(executionNumber);
-      if (exe) {
-        exe->writeResults();
+      if (suffix.size() != 1) {
+        LOG(ERR) << "Invalid suffix";
+        generateError(rest::ResponseCode::NOT_FOUND,
+                      TRI_ERROR_HTTP_NOT_FOUND);
+        return status::DONE;
+      } else if (suffix[0] == "finishedGSS") {
+        LOG(INFO) << "finishedGSS";
+        Conductor *exe = JobMapping::instance()->conductor(executionNumber);
+        if (exe) {
+          exe->finishedGlobalStep(body);
+        } else {
+          LOG(ERR) << "Conductor not found\n";
+        }
+      } else if (suffix[0] == "nextGSS") {
+        LOG(INFO) << "nextGSS";
+        Worker *w = JobMapping::instance()->worker(executionNumber);
+        if (!w) {// can happen if gss == 0
+          LOG(INFO) << "creating worker";
+          w = new Worker(executionNumber, _vocbase, body);
+          JobMapping::instance()->addWorker(w, executionNumber);
+        }
+        w->nextGlobalStep(body);
+      } else if (suffix[0] == "messages") {
+        LOG(INFO) << "messages";
+        Worker *exe = JobMapping::instance()->worker(executionNumber);
+        if (exe) {
+          exe->receivedMessages(body);
+        }
+      } else if (suffix[0] == "writeResults") {
+        Worker *exe = JobMapping::instance()->worker(executionNumber);
+        if (exe) {
+          exe->writeResults();
+        }
       }
+      
+      VPackBuilder result;
+      result.add(VPackValue("thanks"));
+      generateResult(rest::ResponseCode::OK, result.slice());
+      
+    } else {
+      generateError(rest::ResponseCode::METHOD_NOT_ALLOWED,
+                    TRI_ERROR_NOT_IMPLEMENTED, "illegal method for /_api/pregel");
     }
-    
-    VPackBuilder result;
-    result.add(VPackValue("thanks"));
-    generateResult(rest::ResponseCode::OK, result.slice());
-    
-  } else {
-    generateError(rest::ResponseCode::METHOD_NOT_ALLOWED,
-                  TRI_ERROR_NOT_IMPLEMENTED, "illegal method for /_api/pregel");
+  } catch (std::exception const &e) {
+    LOG(ERR) << e.what();
+  } catch(...) {
+    LOG(ERR) << "Exception";
   }
-  
+    
   return status::DONE;
 }
diff --git a/arangod/V8Server/v8-collection.cpp b/arangod/V8Server/v8-collection.cpp
index cac167065f..085becf29b 100644
--- a/arangod/V8Server/v8-collection.cpp
+++ b/arangod/V8Server/v8-collection.cpp
@@ -1850,23 +1850,27 @@ static void JS_Pregel(v8::FunctionCallbackInfo<v8::Value> const& args) {
     LOG(INFO) << "Called as a controller";
     
     TRI_vocbase_t* vocbase = GetContextVocBase(isolate);
-    CollectionID vID;
+    std::shared_ptr<LogicalCollection> vertexColl, edgeColl;
     try {
-      std::shared_ptr<LogicalCollection> const ci1 =
-      ClusterInfo::instance()->getCollection(vocbase->name(), vName);
-      std::shared_ptr<LogicalCollection> const ci2 =
-      ClusterInfo::instance()->getCollection(vocbase->name(), eName);
-      if (ci1->isSystem() || ci2->isSystem()) {
+      vertexColl = ClusterInfo::instance()->getCollection(vocbase->name(), vName);
+      edgeColl = ClusterInfo::instance()->getCollection(vocbase->name(), eName);
+      if (edgeColl->isSystem() || edgeColl->isSystem()) {
         TRI_V8_THROW_EXCEPTION_USAGE("Cannot use pregel on system collection");
       }
-      vID = ci1->cid_as_string();
+      if (!vertexColl->usesDefaultShardKeys()) {
+        TRI_V8_THROW_EXCEPTION_USAGE("Vertex collection needs to be shared after '_key'");
+      }
+      std::vector<std::string> eKeys = edgeColl->shardKeys();
+      if (eKeys.size() != 1 || eKeys[0] == StaticStrings::FromString) {
+        TRI_V8_THROW_EXCEPTION_USAGE("Edge collection needs to be sharded after '_from'");
+      }
       //eName = ci2->cid_as_string();
     } catch (...) {
       TRI_V8_THROW_EXCEPTION_USAGE("Collections do not exist");
     }
 
     result = pregel::JobMapping::instance()->createExecutionNumber();
-    pregel::Conductor* e = new pregel::Conductor(result, vName, vID, eName, "todo");
+    pregel::Conductor* e = new pregel::Conductor(result, vocbase, vertexColl, edgeColl, "todo");
     pregel::JobMapping::instance()->addExecution(e, result);
     
     LOG(INFO) << "Starting...";
diff --git a/arangod/VocBase/LogicalCollection.cpp b/arangod/VocBase/LogicalCollection.cpp
index f5076d3ca3..10a647b60d 100644
--- a/arangod/VocBase/LogicalCollection.cpp
+++ b/arangod/VocBase/LogicalCollection.cpp
@@ -684,6 +684,10 @@ TRI_voc_cid_t LogicalCollection::planId() const {
   return _planId;
 }
 
+std::string LogicalCollection::planId_as_string() const {
+  return basics::StringUtils::itoa(_planId);
+}
+
 TRI_col_type_e LogicalCollection::type() const {
   return _type;
 }
diff --git a/arangod/VocBase/LogicalCollection.h b/arangod/VocBase/LogicalCollection.h
index fd5cf7c69e..5a31610262 100644
--- a/arangod/VocBase/LogicalCollection.h
+++ b/arangod/VocBase/LogicalCollection.h
@@ -130,6 +130,7 @@ class LogicalCollection {
   std::string cid_as_string() const;
 
   TRI_voc_cid_t planId() const;
+  std::string planId_as_string() const;
 
   TRI_col_type_e type() const;