Speed up public stream and remove obsolete indexes

closes diaspora#7944

Author: CSammy

Changelog.md

@@ -1,6 +1,7 @@
 # 0.7.9.0
 
 ## Refactor
+* Improve public stream performance and cleanup unused indexes [#7944](https://github.com/diaspora/diaspora/pull/7944)
 
 ## Bug fixes
 

db/migrate/20181227235201_clean_up_posts_indexes.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class CleanUpPostsIndexes < ActiveRecord::Migration[5.1]
+  def change
+    remove_index :posts, %i[id type created_at]
+    remove_index :posts, :tweet_id
+    add_index :posts, %i[created_at id]
+  end
+end