fix 3-way joins (#9051)

CHANGELOG

@@ -1,6 +1,9 @@
 v3.4.6 (2016-05-21)
 -------------------
 
+* fixed "collection not found" exception during setup of 3-way smart join queries in the
+  cluster
+
 * fixed an edge case of handling `null` values in the AQL function `MIN` for input
   sequences that started with a `null` value. In this case, `null` was always returned as the
   minimum value even though other non-null values may have followed, and `MIN` was supposed

arangod/Aql/EngineInfoContainerDBServer.cpp

@@ -266,6 +266,22 @@ void EngineInfoContainerDBServer::EngineInfo::serializeSnippet(
   infoBuilder.add(VPackValue(arangodb::basics::StringUtils::itoa(_idOfRemoteNode) + ":" + id));
 
   TRI_ASSERT(!_nodes.empty());
+
+  // build up a map of prototypes, e.g. c1 => c2, c2 => c3, c3 => c4,
+  // so we can determine a common prototype ancestor in case we have 3- or 4-way joins
+  std::unordered_map<aql::Collection const*, aql::Collection const*> prototypes;
+  for (auto enIt = _nodes.rbegin(), end = _nodes.rend(); enIt != end; ++enIt) {
+    auto const nodeType = (*enIt)->getType();
+    if (nodeType == ExecutionNode::INDEX || nodeType == ExecutionNode::ENUMERATE_COLLECTION) {
+      auto x = dynamic_cast<CollectionAccessingNode*>(*enIt);
+      auto const* prototype = x->prototypeCollection();
+      if (prototype == nullptr) {
+        continue;
+      }
+      prototypes[x->collection()] = prototype;
+    }
+  }
+
   // copy the relevant fragment of the plan for each shard
   // Note that in these parts of the query there are no SubqueryNodes,
   // since they are all on the coordinator!
@@ -292,6 +308,15 @@ void EngineInfoContainerDBServer::EngineInfo::serializeSnippet(
     if (nodeType == ExecutionNode::INDEX || nodeType == ExecutionNode::ENUMERATE_COLLECTION) {
       auto x = dynamic_cast<CollectionAccessingNode*>(clone);
       auto const* prototype = x->prototypeCollection();
+      // find prototypes of prototypes
+      while (prototype != nullptr) {
+        auto it = prototypes.find(prototype);
+        if (it == prototypes.end()) {
+          break;
+        }
+        prototype = (*it).second;
+      }
+
       if (prototype != nullptr) {
         auto s1 = prototype->shardIds();
         auto s2 = x->collection()->shardIds();