Optimize size of Node and Array

The size of Node and Array decresed from 64 and 128 to 56 and 112.
Some redundant code removed in Spec class.

src/realm/array.hpp

@@ -532,10 +532,10 @@ class Array : public Node, public ArrayParent {
     Getter m_getter = nullptr; // cached to avoid indirection
     const VTable* m_vtable = nullptr;
 
-    uint_least8_t m_width = 0; // Size of an element (meaning depend on type of array).
     int64_t m_lbound;          // min number that can be stored with current m_width
     int64_t m_ubound;          // max number that can be stored with current m_width
 
+    uint8_t m_width = 0;         // Size of an element (meaning depend on type of array).
     bool m_is_inner_bptree_node; // This array is an inner node of B+-tree.
     bool m_has_refs;             // Elements whose first bit is zero are refs to subarrays.
     bool m_context_flag;         // Meaning depends on context.

src/realm/node.hpp

@@ -243,11 +243,7 @@ class Node : public NodeHeader {
     void set_parent(ArrayParent* parent, size_t ndx_in_parent) noexcept
     {
         m_parent = parent;
-        m_ndx_in_parent = ndx_in_parent;
-    }
-    void set_ndx_in_parent(size_t ndx) noexcept
-    {
-        m_ndx_in_parent = ndx;
+        m_ndx_in_parent = unsigned(ndx_in_parent);
     }
 
     void clear_missing_parent_update()
@@ -339,7 +335,7 @@ class Node : public NodeHeader {
 private:
     friend class NodeTree;
     ArrayParent* m_parent = nullptr;
-    size_t m_ndx_in_parent = 0; // Ignored if m_parent is null.
+    unsigned m_ndx_in_parent = 0; // Ignored if m_parent is null.
     bool m_missing_parent_update = false;
 
     void do_copy_on_write(size_t minimum_size = 0);

src/realm/search_index.hpp

@@ -116,7 +116,6 @@ class SearchIndex {
     bool is_attached() const noexcept;
     void set_parent(ArrayParent* parent, size_t ndx_in_parent) noexcept;
     size_t get_ndx_in_parent() const noexcept;
-    void set_ndx_in_parent(size_t ndx_in_parent) noexcept;
     void update_from_parent() noexcept;
     void refresh_accessor_tree(const ClusterColumn& target_column);
     ref_type get_ref() const noexcept;
@@ -174,11 +173,6 @@ inline size_t SearchIndex::get_ndx_in_parent() const noexcept
     return m_root_array->get_ndx_in_parent();
 }
 
-inline void SearchIndex::set_ndx_in_parent(size_t ndx_in_parent) noexcept
-{
-    m_root_array->set_ndx_in_parent(ndx_in_parent);
-}
-
 inline void SearchIndex::update_from_parent() noexcept
 {
     m_root_array->update_from_parent();

src/realm/spec.cpp

@@ -41,16 +41,13 @@ void Spec::init(MemRef mem) noexcept
 {
     m_top.init_from_mem(mem);
     size_t top_size = m_top.size();
-    REALM_ASSERT(top_size > s_attributes_ndx && top_size <= s_spec_max_size);
+    // Since Core6 we will always have the column keys array
+    REALM_ASSERT(top_size == s_spec_max_size);
 
     m_types.init_from_ref(m_top.get_as_ref(s_types_ndx));
     m_names.init_from_ref(m_top.get_as_ref(s_names_ndx));
     m_attr.init_from_ref(m_top.get_as_ref(s_attributes_ndx));
 
-    while (m_top.size() < s_spec_max_size) {
-        m_top.add(0);
-    }
-
     // Enumkeys array is only there when there are StringEnum columns
     if (auto ref = m_top.get_as_ref(s_enum_keys_ndx)) {
         m_enumkeys.init_from_ref(ref);
@@ -59,34 +56,22 @@ void Spec::init(MemRef mem) noexcept
         m_enumkeys.detach();
     }
 
-    if (m_top.get_as_ref(s_col_keys_ndx) == 0) {
-        // This is an upgrade - create column key array
-        MemRef mem_ref = Array::create_empty_array(Array::type_Normal, false, m_top.get_alloc()); // Throws
-        m_keys.init_from_mem(mem_ref);
-        m_keys.update_parent();
-        size_t num_cols = m_types.size();
-        for (size_t i = 0; i < num_cols; i++) {
-            m_keys.add(i);
-        }
-    }
-    else {
-        m_keys.init_from_parent();
-    }
-
+    m_keys.init_from_parent();
 
     update_internals();
 }
 
 void Spec::update_internals() noexcept
 {
-    m_num_public_columns = 0;
     size_t n = m_types.size();
-    for (size_t i = 0; i < n; ++i) {
-        if (ColumnType(int(m_types.get(i))) == col_type_BackLink) {
-            // Now we have no more public columns
+    m_num_public_columns = n;
+    // We normally have fewer backlink columns than public columns, so quicker to go backwards
+    for (size_t i = n; i; --i) {
+        if (ColumnType(int(m_types.get(i - 1))) != col_type_BackLink) {
+            // Now we have no more backlink columns. The rest must be public
             return;
         }
-        m_num_public_columns++;
+        m_num_public_columns--;
     }
 }
 
@@ -207,8 +192,6 @@ void Spec::insert_column(size_t column_ndx, ColKey col_key, ColumnType type, Str
     if (m_enumkeys.is_attached() && type != col_type_BackLink) {
         m_enumkeys.insert(column_ndx, 0);
     }
-
-    update_internals();
 }
 
 void Spec::erase_column(size_t column_ndx)
@@ -246,8 +229,6 @@ void Spec::erase_column(size_t column_ndx)
     m_types.erase(column_ndx); // Throws
     m_attr.erase(column_ndx);  // Throws
     m_keys.erase(column_ndx);
-
-    update_internals();
 }
 
 void Spec::upgrade_string_to_enum(size_t column_ndx, ref_type keys_ref)

src/realm/spec.hpp

@@ -81,7 +81,6 @@ class Spec {
     void destroy() noexcept;
 
     size_t get_ndx_in_parent() const noexcept;
-    void set_ndx_in_parent(size_t) noexcept;
 
     void verify() const;
 
@@ -177,11 +176,6 @@ inline size_t Spec::get_ndx_in_parent() const noexcept
     return m_top.get_ndx_in_parent();
 }
 
-inline void Spec::set_ndx_in_parent(size_t ndx) noexcept
-{
-    m_top.set_ndx_in_parent(ndx);
-}
-
 inline ref_type Spec::get_ref() const noexcept
 {
     return m_top.get_ref();

src/realm/table.hpp

@@ -838,8 +838,6 @@ class Table {
 
     util::Logger* get_logger() const noexcept;
 
-    void set_ndx_in_parent(size_t ndx_in_parent) noexcept;
-
     /// Refresh the part of the accessor tree that is rooted at this
     /// table.
     void refresh_accessor_tree();
@@ -1340,12 +1338,6 @@ inline bool Table::is_link_type(ColumnType col_type) noexcept
     return col_type == col_type_Link;
 }
 
-inline void Table::set_ndx_in_parent(size_t ndx_in_parent) noexcept
-{
-    REALM_ASSERT(m_top.is_attached());
-    m_top.set_ndx_in_parent(ndx_in_parent);
-}
-
 inline size_t Table::colkey2spec_ndx(ColKey key) const
 {
     auto leaf_idx = key.get_index();