clear traverser cache in-between (#8772)

arangod/Aql/TraversalExecutor.cpp

@@ -26,6 +26,7 @@
 #include "Aql/Query.h"
 #include "Aql/SingleRowFetcher.h"
 #include "Graph/Traverser.h"
+#include "Graph/TraverserCache.h"
 #include "Graph/TraverserOptions.h"
 
 using namespace arangodb;
@@ -246,6 +247,8 @@ ExecutionState TraversalExecutor::computeState() const {
 }
 
 bool TraversalExecutor::resetTraverser() {
+  _traverser.traverserCache()->clear();
+
   // Initialize the Expressions within the options.
   // We need to find the variable and read its value here. Everything is
   // computed right now.

arangod/Graph/TraverserCache.cpp

@@ -52,6 +52,12 @@ TraverserCache::TraverserCache(aql::Query* query)
 }
 
 TraverserCache::~TraverserCache() {}
+  
+void TraverserCache::clear() {
+  _stringHeap->clear();
+  _persistedStrings.clear();
+  _mmdr->clear();
+}
 
 VPackSlice TraverserCache::lookupToken(EdgeDocumentToken const& idToken) {
   TRI_ASSERT(!ServerState::instance()->isCoordinator());

arangod/Graph/TraverserCache.h

@@ -59,6 +59,9 @@ class TraverserCache {
 
   virtual ~TraverserCache();
 
+  /// @brief clears all allocated memory in the underlying StringHeap
+  void clear();
+
   //////////////////////////////////////////////////////////////////////////////
   /// @brief Inserts the real document stored within the token
   ///        into the given builder.

arangod/Graph/TraverserOptions.h

@@ -48,11 +48,6 @@ class TraversalNode;
 struct Variable;
 }  // namespace aql
 
-namespace graph {
-class EdgeUniquenessChecker;
-class TraverserCache;
-}  // namespace graph
-
 namespace traverser {
 
 class ClusterTraverser;

lib/Basics/StringHeap.cpp

@@ -58,6 +58,16 @@ arangodb::velocypack::StringRef StringHeap::registerString(char const* ptr, size
   return arangodb::velocypack::StringRef(position, length);
 }
 
+void StringHeap::clear() {
+  _current = nullptr;
+  _end = nullptr;
+
+  for (auto& it : _blocks) {
+    delete[] it;
+  }
+  _blocks.clear();
+}
+
 void StringHeap::merge(StringHeap&& heap) {
   _blocks.reserve(_blocks.size() + heap._blocks.size());
   _blocks.insert(_blocks.end(), heap._blocks.begin(), heap._blocks.end());

lib/Basics/StringHeap.h

@@ -43,6 +43,11 @@ class StringHeap {
   arangodb::velocypack::StringRef registerString(arangodb::velocypack::StringRef const& str) {
     return registerString(str.data(), str.size());
   }
+ 
+  /// @brief clear all data from the StringHeap, not releasing any occupied memory 
+  /// the caller must make sure that nothing points into the data of the StringHeap
+  /// when calling this method
+  void clear();
   
   void merge(StringHeap&& heap);