Remove unused index on project_mirror_data

changelogs/unreleased/remove-unused-project-import-state-index.yml

+---
+title: Remove unused index on project_mirror_data
+merge_request: 22647
+author:
+type: performance

db/migrate/20200108233040_remove_index_project_mirror_data_on_jid.rb

+# frozen_string_literal: true
+
+class RemoveIndexProjectMirrorDataOnJid < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    remove_concurrent_index :project_mirror_data, :jid
+  end
+
+  def down
+    add_concurrent_index :project_mirror_data, :jid
+  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_01_08_155731) do
+ActiveRecord::Schema.define(version: 2020_01_08_233040) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -3200,7 +3200,6 @@ ActiveRecord::Schema.define(version: 2020_01_08_155731) do
     t.text "last_error"
     t.datetime_with_timezone "last_update_at"
     t.datetime_with_timezone "last_successful_update_at"
-    t.index ["jid"], name: "index_project_mirror_data_on_jid"
     t.index ["last_successful_update_at"], name: "index_project_mirror_data_on_last_successful_update_at"
     t.index ["last_update_at", "retry_count"], name: "index_project_mirror_data_on_last_update_at_and_retry_count"
     t.index ["next_execution_timestamp", "retry_count"], name: "index_mirror_data_on_next_execution_and_retry_count"