truncate optimization

arangod/Indexes/PrimaryIndex.cpp

@@ -354,6 +354,11 @@ void PrimaryIndex::invokeOnAllElements(
   _primaryIndex->invokeOnAllElements(work);
 }
 
+void PrimaryIndex::invokeOnAllElementsForRemoval(
+    std::function<void(TRI_doc_mptr_t*)> work) {
+  _primaryIndex->invokeOnAllElementsForRemoval(work);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief checks whether the index supports the condition
 ////////////////////////////////////////////////////////////////////////////////

arangod/Indexes/PrimaryIndex.h

@@ -238,6 +238,7 @@ class PrimaryIndex final : public Index {
   static uint64_t calculateHash(arangodb::Transaction*, uint8_t const*);
 
   void invokeOnAllElements(std::function<void(TRI_doc_mptr_t*)>);
+  void invokeOnAllElementsForRemoval(std::function<void(TRI_doc_mptr_t*)>);
 
   bool supportsFilterCondition(arangodb::aql::AstNode const*,
                                arangodb::aql::Variable const*, size_t, size_t&,

arangod/Utils/Transaction.cpp

@@ -1481,7 +1481,7 @@ OperationResult Transaction::truncateLocal(std::string const& collectionName,
   };
 
   try {
-    primaryIndex->invokeOnAllElements(callback);
+    primaryIndex->invokeOnAllElementsForRemoval(callback);
   }
   catch (basics::Exception const& ex) {
     unlock(trxCollection(cid), TRI_TRANSACTION_WRITE);

lib/Basics/AssocUnique.h

@@ -844,10 +844,30 @@ class AssocUnique {
   
   //////////////////////////////////////////////////////////////////////////////
   /// @brief a method to iterate over all elements in the hash. this method
-  /// can be used for deleting elements as well
+  /// can NOT be used for deleting elements
   //////////////////////////////////////////////////////////////////////////////
 
   void invokeOnAllElements(CallbackElementFuncType callback) {
+    for (auto& b : _buckets) {
+      if (b._table == nullptr) {
+        continue;
+      }
+      for (size_t i = 0; i < b._nrAlloc; ++i) {
+        if (b._table[i] == nullptr) {
+          continue;
+        }
+        // don't increment i
+        callback(b._table[i]);
+      }
+    }
+  }
+
+  //////////////////////////////////////////////////////////////////////////////
+  /// @brief a method to iterate over all elements in the hash. this method
+  /// can be used for deleting elements as well
+  //////////////////////////////////////////////////////////////////////////////
+
+  void invokeOnAllElementsForRemoval(CallbackElementFuncType callback) {
     for (auto& b : _buckets) {
       if (b._table == nullptr) {
         continue;
@@ -857,11 +877,15 @@ class AssocUnique {
           ++i;
           continue;
         }
-        // don't increment i
+        // intentionally don't increment i
+        auto old = b._table[i];
         callback(b._table[i]);
         if (b._nrUsed == 0) {
           break;
         }
+        if (b._table[i] == old) {
+          ++i;
+        }
       }
     }
   }