lib/mobilizon/events/events.ex

@@ -602,7 +602,7 @@ defmodule Mobilizon.Events do
     |> filter_local_or_from_followed_instances_events()
     |> filter_public_visibility()
     |> event_order(Map.get(args, :sort_by, :match_desc), search_string)
-    |> Page.build_page(page, limit, :begins_on)
+    |> Page.build_page(page, limit)
   end
 
   @doc """

lib/mobilizon/instances/instances.ex

@@ -73,7 +73,7 @@ defmodule Mobilizon.Instances do
           query
       end
 
-    %Page{elements: elements} = paged_instances = Page.build_page(query, page, limit, :domain)
+    %Page{elements: elements} = paged_instances = Page.build_page(query, page, limit)
 
     %Page{
       paged_instances

lib/mobilizon/storage/page.ex

@@ -23,11 +23,22 @@ defmodule Mobilizon.Storage.Page do
   `field` is use to define the field that will be used for the count aggregate, which should be the same as the field used for order_by
     See https://stackoverflow.com/q/12693089/10204399
   """
-  @spec build_page(Ecto.Queryable.t(), integer | nil, integer | nil, atom()) :: t(any)
-  def build_page(query, page, limit, field \\ :id) do
+  @spec build_page(Ecto.Queryable.t(), integer | nil, integer) :: t(any)
+  def build_page(query, page, limit) do
+    count_query =
+      query
+      # Exclude select because we add a new one below
+      |> exclude(:select)
+      # Exclude order_by for perf
+      |> exclude(:order_by)
+      # Exclude preloads to avoid error "cannot preload associations in subquery"
+      |> exclude(:preload)
+      |> subquery()
+      |> select([r], count(fragment("*")))
+
     [total, elements] =
       [
-        fn -> Repo.aggregate(query, :count, field) end,
+        fn -> Repo.one(count_query) end,
         fn -> Repo.all(paginate(query, page, limit)) end
       ]
       |> Enum.map(&Task.async/1)