Split alters rather than work with indexes

priv/repo/migrations/20170522160642_case_insensivtivity.exs

@@ -1,22 +1,28 @@
 defmodule Pleroma.Repo.Migrations.CaseInsensivtivity do
   use Ecto.Migration
 
+  # Two-steps alters are intentional.
+  # When alter of 2 columns is done in a single operation,
+  # inconsistent failures happen because of index on `email` column.
+
   def up do
     execute("create extension if not exists citext")
 
-    drop_if_exists(index(:users, [:email]))
-
     alter table(:users) do
       modify(:email, :citext)
-      modify(:nickname, :citext)
     end
 
-    create_if_not_exists(index(:users, [:email]))
+    alter table(:users) do
+      modify(:nickname, :citext)
+    end
   end
 
   def down do
     alter table(:users) do
       modify(:email, :string)
+    end
+
+    alter table(:users) do
       modify(:nickname, :string)
     end