Start to sort out ScatterBlock's special API.

arangod/Aql/ExecutionBlock.cpp

@@ -3758,6 +3758,23 @@ size_t ScatterBlock::skipSomeForShard (size_t atLeast, size_t atMost, std::strin
   return skipped;
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// @brief skipForShard
+////////////////////////////////////////////////////////////////////////////////
+
+bool ScatterBlock::skipForShard (size_t number, std::string const& shardId) {
+  size_t skipped = skipSomeForShard(number, number, shardId);
+  size_t nr = skipped;
+  while ( nr != 0 && skipped < number ){
+    nr = skipSomeForShard(number - skipped, number - skipped, shardId);
+    skipped += nr;
+  }
+  if (nr == 0) {
+    return true;
+  }
+  return ! hasMoreForShard(shardId);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief getClientId: get the number <clientId> (used internally)
 /// corresponding to <shardId>
@@ -3824,6 +3841,9 @@ ClusterCommResult* RemoteBlock::sendRequest (
   ClientTransactionID const clientTransactionId = "AQL";
   CoordTransactionID const coordTransactionId = 1;
   std::map<std::string, std::string> headers;
+  if (! _ownName.empty()) {
+    headers.insert(make_pair("Shard-Id", _ownName));
+  }
 
 std::cout << "SENDING REQUEST TO " << _server << ", URLPART: " << urlPart << ", QUERYID: " << _queryId << "\n";
   return cc->syncRequest(clientTransactionId,

arangod/Aql/ExecutionBlock.h

@@ -1629,6 +1629,12 @@ namespace triagens {
         size_t skipSomeForShard (size_t atLeast, size_t atMost, std::string
             const& shardId);
 
+////////////////////////////////////////////////////////////////////////////////
+/// @brief skipForShard
+////////////////////////////////////////////////////////////////////////////////
+
+        bool skipForShard (size_t number, std::string const& shardId);
+
       private: 
        
 ////////////////////////////////////////////////////////////////////////////////

arangod/Aql/RestAqlHandler.cpp

@@ -706,7 +706,16 @@ std::cout << "ANSWERBODY: " << JsonHelper::toString(answerBody.json()) << "\n\n"
                                "atMost", ExecutionBlock::DefaultBatchSize);
     size_t skipped;
     try {
-      skipped = query->engine()->skipSome(atLeast, atMost);
+      if (shardId.empty()) {
+        skipped = query->engine()->skipSome(atLeast, atMost);
+      }
+      else {
+        auto scatter = static_cast<ScatterBlock*>(query->engine()->root());
+        if (scatter->getPlanNode()->getType() != ExecutionNode::SCATTER) {
+          THROW_ARANGO_EXCEPTION(TRI_ERROR_INTERNAL);
+        }
+        skipped = scatter->skipSomeForShard(atLeast, atMost, shardId);
+      }
     }
     catch (...) {
       generateError(HttpResponse::SERVER_ERROR, TRI_ERROR_HTTP_SERVER_ERROR,
@@ -720,7 +729,18 @@ std::cout << "ANSWERBODY: " << JsonHelper::toString(answerBody.json()) << "\n\n"
     auto number = JsonHelper::getNumericValue<uint64_t>(queryJson.json(),
                                                         "number", 1);
     try {
-      bool exhausted = query->engine()->skip(number);
+      bool exhausted;
+      if (shardId.empty()) {
+        exhausted = query->engine()->skip(number);
+      }
+      else {
+        auto scatter = static_cast<ScatterBlock*>(query->engine()->root());
+        if (scatter->getPlanNode()->getType() != ExecutionNode::SCATTER) {
+          THROW_ARANGO_EXCEPTION(TRI_ERROR_INTERNAL);
+        }
+        exhausted = scatter->skipForShard(number, shardId);
+      }
+
       answerBody("exhausted", Json(exhausted))
                 ("error", Json(false));
     }