diff --git a/src/buddies/src/bd/strmxor.cc b/src/buddies/src/bd/strmxor.cc
index ba165cd4b..876373056 100644
--- a/src/buddies/src/bd/strmxor.cc
+++ b/src/buddies/src/bd/strmxor.cc
@@ -554,6 +554,7 @@ bool run_deep_xor (const XORData &xor_data)
 {
   db::DeepShapeStore dss;
   dss.set_threads (xor_data.threads);
+  dss.set_keep_layouts (true);  //  avoids excessive cell mapping
 
   double dbu = std::min (xor_data.layout_a->dbu (), xor_data.layout_b->dbu ());
 
diff --git a/src/db/db/dbDeepShapeStore.cc b/src/db/db/dbDeepShapeStore.cc
index 74e8f6e8b..e62c2cfd9 100644
--- a/src/db/db/dbDeepShapeStore.cc
+++ b/src/db/db/dbDeepShapeStore.cc
@@ -154,17 +154,25 @@ DeepLayer::add_from (const DeepLayer &dl)
     db::cell_index_type source_cell = dl.initial_cell ().cell_index ();
     const db::Layout *source_layout = &dl.layout ();
 
-    db::CellMapping cm;
-    cm.create_from_geometry_full (*into_layout, into_cell, *source_layout, source_cell);
+    //  create or reuse a layout mapping
 
-    //  Actually copy the shapes
+    const db::CellMapping *cell_mapping = 0;
+    db::CellMapping cm;
+    if (store () == dl.store ()) {
+      cell_mapping = &const_cast<db::DeepShapeStore *> (mp_store.get ())->internal_cell_mapping (layout_index (), dl.layout_index ());
+    } else {
+      cm.create_from_geometry_full (*into_layout, into_cell, *source_layout, source_cell);
+      cell_mapping = &cm;
+    }
+
+    //  actually copy the shapes
 
     std::map<unsigned int, unsigned int> lm;
     lm.insert (std::make_pair (dl.layer (), layer ()));
 
     std::vector <db::cell_index_type> source_cells;
     source_cells.push_back (source_cell);
-    db::copy_shapes (*into_layout, *source_layout, db::ICplxTrans (), source_cells, cm.table (), lm);
+    db::copy_shapes (*into_layout, *source_layout, db::ICplxTrans (), source_cells, cell_mapping->table (), lm);
 
   }
 }
@@ -418,11 +426,13 @@ static unsigned int init_layer (db::Layout &layout, const db::RecursiveShapeIter
 }
 
 DeepShapeStore::DeepShapeStore ()
+  : m_keep_layouts (false)
 {
   ++s_instance_count;
 }
 
 DeepShapeStore::DeepShapeStore (const std::string &topcell_name, double dbu)
+  : m_keep_layouts (false)
 {
   ++s_instance_count;
 
@@ -711,6 +721,16 @@ db::Layout &DeepShapeStore::layout (unsigned int n)
   return m_layouts [n]->layout;
 }
 
+unsigned int DeepShapeStore::layout_index (const db::Layout *layout) const
+{
+  for (std::vector<LayoutHolder *>::const_iterator i = m_layouts.begin (); i != m_layouts.end (); ++i) {
+    if (&(*i)->layout == layout) {
+      return (unsigned int) (i - m_layouts.begin ());
+    }
+  }
+  tl_assert (false);
+}
+
 size_t DeepShapeStore::instance_count ()
 {
   return s_instance_count;
@@ -743,7 +763,7 @@ void DeepShapeStore::remove_ref (unsigned int layout, unsigned int layer)
 
   }
 
-  if ((m_layouts[layout]->refs -= 1) <= 0) {
+  if ((m_layouts[layout]->refs -= 1) <= 0 && ! m_keep_layouts) {
     delete m_layouts[layout];
     m_layouts[layout] = 0;
     clear_breakout_cells (layout);
@@ -919,6 +939,7 @@ void
 DeepShapeStore::invalidate_hier ()
 {
   m_delivery_mapping_cache.clear ();
+  m_internal_mapping_cache.clear ();
 }
 
 void
@@ -934,6 +955,26 @@ DeepShapeStore::issue_variants (unsigned int layout_index, const std::map<db::ce
   }
 }
 
+const db::CellMapping &
+DeepShapeStore::internal_cell_mapping (unsigned int from_layout_index, unsigned int into_layout_index)
+{
+  std::map<std::pair<unsigned int, unsigned int>, db::CellMapping>::iterator cm = m_internal_mapping_cache.find (std::make_pair (from_layout_index, into_layout_index));
+  if (cm == m_internal_mapping_cache.end ()) {
+
+    cm = m_internal_mapping_cache.insert (std::make_pair (std::make_pair (from_layout_index, into_layout_index), db::CellMapping ())).first;
+
+    db::Layout &into_layout = layout (into_layout_index);
+    db::cell_index_type into_cell = initial_cell (into_layout_index).cell_index ();
+    const db::Layout &source_layout = layout (from_layout_index);
+    db::cell_index_type source_cell = initial_cell (from_layout_index).cell_index ();
+
+    cm->second.create_from_geometry_full (into_layout, into_cell, source_layout, source_cell);
+
+  }
+
+  return cm->second;
+}
+
 const db::CellMapping &
 DeepShapeStore::cell_mapping_to_original (unsigned int layout_index, db::Layout *into_layout, db::cell_index_type into_cell, const std::set<db::cell_index_type> *excluded_cells, const std::set<db::cell_index_type> *included_cells)
 {
diff --git a/src/db/db/dbDeepShapeStore.h b/src/db/db/dbDeepShapeStore.h
index 9532ffd2b..990ecfb2e 100644
--- a/src/db/db/dbDeepShapeStore.h
+++ b/src/db/db/dbDeepShapeStore.h
@@ -339,6 +339,25 @@ public:
    */
   bool is_singular () const;
 
+  /**
+   *  @brief Sets a value indicating whether to keep layouts
+   *
+   *  If this value is set to true, layouts are not released when their reference count
+   *  goes down to zero.
+   */
+  void set_keep_layouts (bool f)
+  {
+    m_keep_layouts = f;
+  }
+
+  /**
+   *  @brief Gets a value indicating whether to keep layouts
+   */
+  bool keep_layouts () const
+  {
+    return m_keep_layouts;
+  }
+
   /**
    *  @brief Creates a new layer from a flat region (or the region is made flat)
    *
@@ -479,6 +498,11 @@ public:
    */
   const db::CellMapping &cell_mapping_to_original (unsigned int layout_index, db::Layout *into_layout, db::cell_index_type into_cell, const std::set<db::cell_index_type> *excluded_cells = 0, const std::set<db::cell_index_type> *included_cells = 0);
 
+  /**
+   *  @brief Gets the cell mapping from one internal layout to another
+   */
+  const db::CellMapping &internal_cell_mapping (unsigned int from_layout_index, unsigned int into_layout_index);
+
   /**
    *  @brief Create cell variants from the given variant collector
    *
@@ -544,6 +568,11 @@ public:
    */
   db::Cell &initial_cell (unsigned int n);
 
+  /**
+   *  @brief Gets the layout index for a given internal layout
+   */
+  unsigned int layout_index (const db::Layout *layout) const;
+
   /**
    *  @brief Gets the singular layout (const version)
    *
@@ -752,6 +781,7 @@ private:
   layout_map_type m_layout_map;
   DeepShapeStoreState m_state;
   std::list<DeepShapeStoreState> m_state_stack;
+  bool m_keep_layouts;
   tl::Mutex m_lock;
 
   struct DeliveryMappingCacheKey
@@ -781,6 +811,7 @@ private:
   };
 
   std::map<DeliveryMappingCacheKey, db::CellMapping> m_delivery_mapping_cache;
+  std::map<std::pair<unsigned int, unsigned int>, db::CellMapping> m_internal_mapping_cache;
 };
 
 template <class VarCollector>