Improve legacy query to retrieve projects when selective sync is enabled

ee/app/models/concerns/geo/selective_sync.rb

@@ -14,4 +14,51 @@ module Geo::SelectiveSync
   def selective_sync_by_shards?
     selective_sync_type == 'shards'
   end
+
+  private
+
+  def selected_namespaces_and_descendants
+    relation = selected_namespaces_and_descendants_cte.apply_to(namespaces_model.all)
+    relation.extend(Gitlab::Database::ReadOnlyRelation)
+    relation
+  end
+
+  def selected_namespaces_and_descendants_cte
+    cte = Gitlab::SQL::RecursiveCTE.new(:base_and_descendants)
+
+    cte << geo_node_namespace_links
+      .select(geo_node_namespace_links_table[:namespace_id].as('id'))
+      .except(:order)
+
+    # Recursively get all the descendants of the base set.
+    cte << namespaces_model
+      .select(namespaces_table[:id])
+      .from([namespaces_table, cte.table])
+      .where(namespaces_table[:parent_id].eq(cte.table[:id]))
+      .except(:order)
+
+    cte
+  end
+
+  # This concern doesn't define a namespaces relation. That's done in ::GeoNode
+  # or ::Geo::Fdw::GeoNode respectively. So when we use the same code from the
+  # two places, they act differently - the first doesn't use FDW, the second does.
+  def namespaces_model
+    namespaces.model
+  end
+
+  # This concern doesn't define a namespaces relation. That's done in ::GeoNode
+  # or ::Geo::Fdw::GeoNode respectively. So when we use the same code from the
+  # two places, they act differently - the first doesn't use FDW, the second does.
+  def namespaces_table
+    namespaces.arel_table
+  end
+
+  # This concern doesn't define a geo_node_namespace_links relation. That's
+  # done in ::GeoNode or ::Geo::Fdw::GeoNode respectively. So when we use the
+  # same code from the two places, they act differently - the first doesn't
+  # use FDW, the second does.
+  def geo_node_namespace_links_table
+    geo_node_namespace_links.arel_table
+  end
 end

ee/app/models/geo/fdw/geo_node.rb

@@ -71,37 +71,6 @@ module Geo
         Gitlab::Geo::Fdw::ProjectRegistryQueryBuilder.new
           .within_shards(selective_sync_shards)
       end
-
-      def selected_namespaces_and_descendants
-        relation = selected_namespaces_and_descendants_cte.apply_to(Geo::Fdw::Namespace.all)
-        relation.extend(Gitlab::Database::ReadOnlyRelation)
-        relation
-      end
-
-      def selected_namespaces_and_descendants_cte
-        cte = Gitlab::SQL::RecursiveCTE.new(:base_and_descendants)
-
-        cte << geo_node_namespace_links
-          .select(fdw_geo_node_namespace_links_table[:namespace_id].as('id'))
-          .except(:order)
-
-        # Recursively get all the descendants of the base set.
-        cte << Geo::Fdw::Namespace
-          .select(fdw_namespaces_table[:id])
-          .from([fdw_namespaces_table, cte.table])
-          .where(fdw_namespaces_table[:parent_id].eq(cte.table[:id]))
-          .except(:order)
-
-        cte
-      end
-
-      def fdw_namespaces_table
-        Geo::Fdw::Namespace.arel_table
-      end
-
-      def fdw_geo_node_namespace_links_table
-        Geo::Fdw::GeoNodeNamespaceLink.arel_table
-      end
     end
   end
 end

ee/app/models/geo_node.rb

@@ -204,10 +204,9 @@ class GeoNode < ApplicationRecord
     return Project.all unless selective_sync?
 
     if selective_sync_by_namespaces?
-      query = Gitlab::ObjectHierarchy.new(namespaces).base_and_descendants
-      Project.in_namespace(query.select(:id))
+      projects_for_selected_namespaces
     elsif selective_sync_by_shards?
-      Project.within_shards(selective_sync_shards)
+      projects_for_selected_shards
     else
       Project.none
     end
@@ -316,4 +315,12 @@ class GeoNode < ApplicationRecord
 
     "#{value}/"
   end
+
+  def projects_for_selected_namespaces
+    Project.where(Project.arel_table.name => { namespace_id: selected_namespaces_and_descendants.select(:id) })
+  end
+
+  def projects_for_selected_shards
+    Project.within_shards(selective_sync_shards)
+  end
 end