Add partial index on users.feed_url (#11411)

db/migrate/20201114151157_add_partial_index_to_users_feed_url.rb

@@ -0,0 +1,9 @@
+class AddPartialIndexToUsersFeedUrl < ActiveRecord::Migration[6.0]
+  disable_ddl_transaction!
+
+  def change
+    # adds an index only on users with a feed URL, as they are a tiny percentage of the total
+    # number of users, there is no need to add a full index as most entries will be empty
+    add_index :users, :feed_url, where: "COALESCE(feed_url, '') <> ''", algorithm: :concurrently
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2020_10_19_012200) do
+ActiveRecord::Schema.define(version: 2020_11_14_151157) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "citext"
@@ -1328,6 +1328,7 @@ ActiveRecord::Schema.define(version: 2020_10_19_012200) do
     t.index ["created_at"], name: "index_users_on_created_at"
     t.index ["email"], name: "index_users_on_email", unique: true
     t.index ["facebook_username"], name: "index_users_on_facebook_username"
+    t.index ["feed_url"], name: "index_users_on_feed_url", where: "((COALESCE(feed_url, ''::character varying))::text <> ''::text)"
     t.index ["github_username"], name: "index_users_on_github_username", unique: true
     t.index ["invitation_token"], name: "index_users_on_invitation_token", unique: true
     t.index ["invitations_count"], name: "index_users_on_invitations_count"