FollowingRelationship storage & performance optimizations (state turned ecto_enum-driven integer, reorganized indices etc.).

priv/repo/migrations/20200328124805_change_following_relationships_state_to_integer.exs

@@ -0,0 +1,29 @@
+defmodule Pleroma.Repo.Migrations.ChangeFollowingRelationshipsStateToInteger do
+  use Ecto.Migration
+
+  @alter_apps_scopes "ALTER TABLE following_relationships ALTER COLUMN state"
+
+  def up do
+    execute("""
+    #{@alter_apps_scopes} TYPE integer USING
+    CASE
+      WHEN state = 'pending' THEN 1
+      WHEN state = 'accept' THEN 2
+      WHEN state = 'reject' THEN 3
+      ELSE 0
+    END;
+    """)
+  end
+
+  def down do
+    execute("""
+    #{@alter_apps_scopes} TYPE varchar(255) USING
+    CASE
+      WHEN state = 1 THEN 'pending'
+      WHEN state = 2 THEN 'accept'
+      WHEN state = 3 THEN 'reject'
+      ELSE ''
+    END;
+    """)
+  end
+end

priv/repo/migrations/20200328130139_add_following_relationships_following_id_index.exs

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+defmodule Pleroma.Repo.Migrations.AddFollowingRelationshipsFollowingIdIndex do
+  use Ecto.Migration
+
+  # [:follower_index] index is useless because of [:follower_id, :following_id] index
+  # [:following_id] index makes sense because of user's followers-targeted queries
+  def change do
+    drop_if_exists(index(:following_relationships, [:follower_id]))
+
+    create_if_not_exists(drop_if_exists(index(:following_relationships, [:following_id])))
+  end
+end