diff --git includes/database/query.inc includes/database/query.inc
index 2e775be..7289121 100644
--- includes/database/query.inc
+++ includes/database/query.inc
@@ -773,52 +773,43 @@ class MergeQuery extends Query {
     // Wrap multiple queries in a transaction, if the database supports it.
     $transaction = $this->connection->startTransaction();
 
-    // Manually check if the record already exists.
-    $select = $this->connection->select($this->table);
-    foreach ($this->keyFields as $field => $value) {
-      $select->condition($field, $value);
+    // We want to reduce the number of queries to the minimum so that the
+    // behaviour is as close to atomic as possible. Because our database layer
+    // supports savepoints we can try to insert first, catch the failure if any
+    // and do the update instead with out breaking any transaction we maybe in.
+    try {
+      $insert_fields = $this->insertFields + $this->keyFields;
+      $this->connection->insert($this->table, $this->queryOptions)->fields($insert_fields)->execute();
+      return MergeQuery::STATUS_INSERT;
+    catch (Exception $e) {
+      $transaction->rollback();
     }
 
-    $select = $select->countQuery();
-    $sql = (string) $select;
-    $arguments = $select->getArguments();
-    $num_existing = $this->connection->query($sql, $arguments)->fetchField();
-
-
-    if ($num_existing) {
-      // If there is already an existing record, run an update query.
-
-      if ($this->updateFields) {
-        $update_fields = $this->updateFields;
+    // Should the insert fail, we will assume it is because the record already
+    // exists so lets attempt to update the record instead.
+    if ($this->updateFields) {
+      $update_fields = $this->updateFields;
+    }
+    else {
+      $update_fields = $this->insertFields;
+      // If there are no exclude fields, this is a no-op.
+      foreach ($this->excludeFields as $exclude_field) {
+        unset($update_fields[$exclude_field]);
       }
-      else {
-        $update_fields = $this->insertFields;
-        // If there are no exclude fields, this is a no-op.
-        foreach ($this->excludeFields as $exclude_field) {
-          unset($update_fields[$exclude_field]);
-        }
+    }
+    if ($update_fields || $this->expressionFields) {
+      // Only run the update if there are no fields or expressions to update.
+      $update = $this->connection->update($this->table, $this->queryOptions)->fields($update_fields);
+      foreach ($this->keyFields as $field => $value) {
+        $update->condition($field, $value);
       }
-      if ($update_fields || $this->expressionFields) {
-        // Only run the update if there are no fields or expressions to update.
-        $update = $this->connection->update($this->table, $this->queryOptions)->fields($update_fields);
-        foreach ($this->keyFields as $field => $value) {
-          $update->condition($field, $value);
-        }
-        foreach ($this->expressionFields as $field => $expression) {
-          $update->expression($field, $expression['expression'], $expression['arguments']);
-        }
-        $update->execute();
-        return MergeQuery::STATUS_UPDATE;
+      foreach ($this->expressionFields as $field => $expression) {
+        $update->expression($field, $expression['expression'], $expression['arguments']);
       }
+      $update->execute();
+      return MergeQuery::STATUS_UPDATE;
     }
-    else {
-      // If there is no existing record, run an insert query.
-      $insert_fields = $this->insertFields + $this->keyFields;
-      $this->connection->insert($this->table, $this->queryOptions)->fields($insert_fields)->execute();
-      return MergeQuery::STATUS_INSERT;
-    }
-
-    // Transaction commits here where $transaction looses scope.
+    throw new InvalidMergeQueryException("Unexpected action occured. Merge query did not insert or update a record.");
   }
 
   public function __toString() {