Remove unnecessary database indexes

changelogs/unreleased/removing_unnecessary_indexes.yml

+---
+title: Remove unnecessary database indices
+merge_request: 
+author: 

db/migrate/20161128142110_remove_unnecessary_indexes.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveUnnecessaryIndexes < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+  disable_ddl_transaction!
+
+  DOWNTIME = false
+
+  def up
+    remove_index :labels, column: :group_id if index_exists?(:labels, :group_id)
+    remove_index :award_emoji, column: :user_id if index_exists?(:award_emoji, :user_id)
+    remove_index :ci_builds, column: :commit_id if index_exists?(:ci_builds, :commit_id)
+    remove_index :deployments, column: :project_id if index_exists?(:deployments, :project_id)
+    remove_index :deployments, column: ["project_id", "environment_id"] if index_exists?(:deployments, ["project_id", "environment_id"])
+    remove_index :lists, column: :board_id if index_exists?(:lists, :board_id)
+    remove_index :milestones, column: :project_id if index_exists?(:milestones, :project_id)
+    remove_index :notes, column: :project_id if index_exists?(:notes, :project_id)
+    remove_index :users_star_projects, column: :user_id if index_exists?(:users_star_projects, :user_id)
+  end
+
+  def down
+    add_concurrent_index :labels, :group_id
+    add_concurrent_index :award_emoji, :user_id
+    add_concurrent_index :ci_builds, :commit_id
+    add_concurrent_index :deployments, :project_id
+    add_concurrent_index :deployments, ["project_id", "environment_id"]
+    add_concurrent_index :lists, :board_id
+    add_concurrent_index :milestones, :project_id
+    add_concurrent_index :notes, :project_id
+    add_concurrent_index :users_star_projects, :user_id
+  end
+end

db/schema.rb

@@ -132,7 +132,6 @@ ActiveRecord::Schema.define(version: 20161128161412) do
 
   add_index "award_emoji", ["awardable_type", "awardable_id"], name: "index_award_emoji_on_awardable_type_and_awardable_id", using: :btree
   add_index "award_emoji", ["user_id", "name"], name: "index_award_emoji_on_user_id_and_name", using: :btree
-  add_index "award_emoji", ["user_id"], name: "index_award_emoji_on_user_id", using: :btree
 
   create_table "boards", force: :cascade do |t|
     t.integer "project_id", null: false
@@ -220,7 +219,6 @@ ActiveRecord::Schema.define(version: 20161128161412) do
   add_index "ci_builds", ["commit_id", "status", "type"], name: "index_ci_builds_on_commit_id_and_status_and_type", using: :btree
   add_index "ci_builds", ["commit_id", "type", "name", "ref"], name: "index_ci_builds_on_commit_id_and_type_and_name_and_ref", using: :btree
   add_index "ci_builds", ["commit_id", "type", "ref"], name: "index_ci_builds_on_commit_id_and_type_and_ref", using: :btree
-  add_index "ci_builds", ["commit_id"], name: "index_ci_builds_on_commit_id", using: :btree
   add_index "ci_builds", ["gl_project_id"], name: "index_ci_builds_on_gl_project_id", using: :btree
   add_index "ci_builds", ["project_id"], name: "index_ci_builds_on_project_id", using: :btree
   add_index "ci_builds", ["runner_id"], name: "index_ci_builds_on_runner_id", using: :btree
@@ -410,9 +408,7 @@ ActiveRecord::Schema.define(version: 20161128161412) do
   end
 
   add_index "deployments", ["project_id", "environment_id", "iid"], name: "index_deployments_on_project_id_and_environment_id_and_iid", using: :btree
-  add_index "deployments", ["project_id", "environment_id"], name: "index_deployments_on_project_id_and_environment_id", using: :btree
   add_index "deployments", ["project_id", "iid"], name: "index_deployments_on_project_id_and_iid", unique: true, using: :btree
-  add_index "deployments", ["project_id"], name: "index_deployments_on_project_id", using: :btree
 
   create_table "emails", force: :cascade do |t|
     t.integer "user_id", null: false
@@ -570,7 +566,6 @@ ActiveRecord::Schema.define(version: 20161128161412) do
   end
 
   add_index "labels", ["group_id", "project_id", "title"], name: "index_labels_on_group_id_and_project_id_and_title", unique: true, using: :btree
-  add_index "labels", ["group_id"], name: "index_labels_on_group_id", using: :btree
 
   create_table "lfs_objects", force: :cascade do |t|
     t.string "oid", null: false
@@ -601,7 +596,6 @@ ActiveRecord::Schema.define(version: 20161128161412) do
   end
 
   add_index "lists", ["board_id", "label_id"], name: "index_lists_on_board_id_and_label_id", unique: true, using: :btree
-  add_index "lists", ["board_id"], name: "index_lists_on_board_id", using: :btree
   add_index "lists", ["label_id"], name: "index_lists_on_label_id", using: :btree
 
   create_table "members", force: :cascade do |t|
@@ -727,7 +721,6 @@ ActiveRecord::Schema.define(version: 20161128161412) do
   add_index "milestones", ["description"], name: "index_milestones_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
   add_index "milestones", ["due_date"], name: "index_milestones_on_due_date", using: :btree
   add_index "milestones", ["project_id", "iid"], name: "index_milestones_on_project_id_and_iid", unique: true, using: :btree
-  add_index "milestones", ["project_id"], name: "index_milestones_on_project_id", using: :btree
   add_index "milestones", ["title"], name: "index_milestones_on_title", using: :btree
   add_index "milestones", ["title"], name: "index_milestones_on_title_trigram", using: :gin, opclasses: {"title"=>"gin_trgm_ops"}
 
@@ -790,7 +783,6 @@ ActiveRecord::Schema.define(version: 20161128161412) do
   add_index "notes", ["noteable_id", "noteable_type"], name: "index_notes_on_noteable_id_and_noteable_type", using: :btree
   add_index "notes", ["noteable_type"], name: "index_notes_on_noteable_type", using: :btree
   add_index "notes", ["project_id", "noteable_type"], name: "index_notes_on_project_id_and_noteable_type", using: :btree
-  add_index "notes", ["project_id"], name: "index_notes_on_project_id", using: :btree
   add_index "notes", ["updated_at"], name: "index_notes_on_updated_at", using: :btree
 
   create_table "notification_settings", force: :cascade do |t|
@@ -1243,7 +1235,6 @@ ActiveRecord::Schema.define(version: 20161128161412) do
 
   add_index "users_star_projects", ["project_id"], name: "index_users_star_projects_on_project_id", using: :btree
   add_index "users_star_projects", ["user_id", "project_id"], name: "index_users_star_projects_on_user_id_and_project_id", unique: true, using: :btree
-  add_index "users_star_projects", ["user_id"], name: "index_users_star_projects_on_user_id", using: :btree
 
   create_table "web_hooks", force: :cascade do |t|
     t.string "url", limit: 2000