Merge branch 'remove-unused-indexes' into 'master'

Remove various redundant indexes

## What does this MR do?

This MR removes various redundant and unused indexes. See c3d5c536d9c77dbe183744cb19f2cdab7ee606fd for more information.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

Unused indexes are a waste of storage space and slow down database writes. If they are ever needed again we can re-create them. There's no point in hoarding indexes because you _may_ need them in the future.

## What are the relevant issue numbers?

#20767

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5759

CHANGELOG

@@ -28,6 +28,7 @@ v 8.11.0 (unreleased)
   - Add experimental Redis Sentinel support !1877
   - Fix branches page dropdown sort initial state (ClemMakesApps)
   - Environments have an url to link to
+  - Various redundant database indexes have been removed
   - Update `timeago` plugin to use multiple string/locale settings
   - Remove unused images (ClemMakesApps)
   - Limit git rev-list output count to one in forced push check

db/migrate/20160810142633_remove_redundant_indexes.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveRedundantIndexes < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    indexes = [
+      [:ci_taggings, 'ci_taggings_idx'],
+      [:audit_events, 'index_audit_events_on_author_id'],
+      [:audit_events, 'index_audit_events_on_type'],
+      [:ci_builds, 'index_ci_builds_on_erased_by_id'],
+      [:ci_builds, 'index_ci_builds_on_project_id_and_commit_id'],
+      [:ci_builds, 'index_ci_builds_on_type'],
+      [:ci_commits, 'index_ci_commits_on_project_id'],
+      [:ci_commits, 'index_ci_commits_on_project_id_and_committed_at'],
+      [:ci_commits, 'index_ci_commits_on_project_id_and_committed_at_and_id'],
+      [:ci_commits, 'index_ci_commits_on_project_id_and_sha'],
+      [:ci_commits, 'index_ci_commits_on_sha'],
+      [:ci_events, 'index_ci_events_on_created_at'],
+      [:ci_events, 'index_ci_events_on_is_admin'],
+      [:ci_events, 'index_ci_events_on_project_id'],
+      [:ci_jobs, 'index_ci_jobs_on_deleted_at'],
+      [:ci_jobs, 'index_ci_jobs_on_project_id'],
+      [:ci_projects, 'index_ci_projects_on_gitlab_id'],
+      [:ci_projects, 'index_ci_projects_on_shared_runners_enabled'],
+      [:ci_services, 'index_ci_services_on_project_id'],
+      [:ci_sessions, 'index_ci_sessions_on_session_id'],
+      [:ci_sessions, 'index_ci_sessions_on_updated_at'],
+      [:ci_tags, 'index_ci_tags_on_name'],
+      [:ci_triggers, 'index_ci_triggers_on_deleted_at'],
+      [:identities, 'index_identities_on_created_at_and_id'],
+      [:issues, 'index_issues_on_title'],
+      [:keys, 'index_keys_on_created_at_and_id'],
+      [:members, 'index_members_on_created_at_and_id'],
+      [:members, 'index_members_on_type'],
+      [:milestones, 'index_milestones_on_created_at_and_id'],
+      [:namespaces, 'index_namespaces_on_visibility_level'],
+      [:projects, 'index_projects_on_builds_enabled_and_shared_runners_enabled'],
+      [:services, 'index_services_on_category'],
+      [:services, 'index_services_on_created_at_and_id'],
+      [:services, 'index_services_on_default'],
+      [:snippets, 'index_snippets_on_created_at'],
+      [:snippets, 'index_snippets_on_created_at_and_id'],
+      [:todos, 'index_todos_on_state'],
+      [:web_hooks, 'index_web_hooks_on_created_at_and_id'],
+
+      # These indexes _may_ be used but they can be replaced by other existing
+      # indexes.
+
+      # There's already a composite index on (project_id, iid) which means that
+      # a separate index for _just_ project_id is not needed.
+      [:issues, 'index_issues_on_project_id'],
+
+      # These are all composite indexes for the columns (created_at, id). In all
+      # these cases there's already a standalone index for "created_at" which
+      # can be used instead.
+      #
+      # Because the "id" column of these composite indexes is never needed (due
+      # to "id" already being indexed as its a primary key) these composite
+      # indexes are useless.
+      [:issues, 'index_issues_on_created_at_and_id'],
+      [:merge_requests, 'index_merge_requests_on_created_at_and_id'],
+      [:namespaces, 'index_namespaces_on_created_at_and_id'],
+      [:notes, 'index_notes_on_created_at_and_id'],
+      [:projects, 'index_projects_on_created_at_and_id'],
+      [:users, 'index_users_on_created_at_and_id'],
+    ]
+
+    transaction do
+      indexes.each do |(table, index)|
+        remove_index(table, name: index) if index_exists_by_name?(table, index)
+      end
+    end
+
+    add_concurrent_index(:users, :created_at)
+    add_concurrent_index(:projects, :created_at)
+    add_concurrent_index(:namespaces, :created_at)
+  end
+
+  def down
+    # We're only restoring the composite indexes that could be replaced with
+    # individual ones, just in case somebody would ever want to revert.
+    transaction do
+      remove_index(:users, :created_at)
+      remove_index(:projects, :created_at)
+      remove_index(:namespaces, :created_at)
+    end
+
+    [:issues, :merge_requests, :namespaces, :notes, :projects, :users].each do |table|
+      add_concurrent_index(table, [:created_at, :id],
+                           name: "index_#{table}_on_created_at_and_id")
+    end
+  end
+
+  # Rails' index_exists? doesn't work when you only give it a table and index
+  # name. As such we have to use some extra code to check if an index exists for
+  # a given name.
+  def index_exists_by_name?(table, index)
+    indexes_for_table[table].include?(index)
+  end
+
+  def indexes_for_table
+    @indexes_for_table ||= Hash.new do |hash, table_name|
+      hash[table_name] = indexes(table_name).map(&:name)
+    end
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160810102349) do
+ActiveRecord::Schema.define(version: 20160810142633) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -102,9 +102,7 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.datetime "updated_at"
   end
 
-  add_index "audit_events", ["author_id"], name: "index_audit_events_on_author_id", using: :btree
   add_index "audit_events", ["entity_id", "entity_type"], name: "index_audit_events_on_entity_id_and_entity_type", using: :btree
-  add_index "audit_events", ["type"], name: "index_audit_events_on_type", using: :btree
 
   create_table "award_emoji", force: :cascade do |t|
     t.string   "name"
@@ -179,13 +177,10 @@ ActiveRecord::Schema.define(version: 20160810102349) do
   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", ["erased_by_id"], name: "index_ci_builds_on_erased_by_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", "commit_id"], name: "index_ci_builds_on_project_id_and_commit_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
   add_index "ci_builds", ["status"], name: "index_ci_builds_on_status", using: :btree
-  add_index "ci_builds", ["type"], name: "index_ci_builds_on_type", using: :btree
 
   create_table "ci_commits", force: :cascade do |t|
     t.integer  "project_id"
@@ -209,11 +204,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
   add_index "ci_commits", ["gl_project_id", "sha"], name: "index_ci_commits_on_gl_project_id_and_sha", using: :btree
   add_index "ci_commits", ["gl_project_id", "status"], name: "index_ci_commits_on_gl_project_id_and_status", using: :btree
   add_index "ci_commits", ["gl_project_id"], name: "index_ci_commits_on_gl_project_id", using: :btree
-  add_index "ci_commits", ["project_id", "committed_at", "id"], name: "index_ci_commits_on_project_id_and_committed_at_and_id", using: :btree
-  add_index "ci_commits", ["project_id", "committed_at"], name: "index_ci_commits_on_project_id_and_committed_at", using: :btree
-  add_index "ci_commits", ["project_id", "sha"], name: "index_ci_commits_on_project_id_and_sha", using: :btree
-  add_index "ci_commits", ["project_id"], name: "index_ci_commits_on_project_id", using: :btree
-  add_index "ci_commits", ["sha"], name: "index_ci_commits_on_sha", using: :btree
   add_index "ci_commits", ["status"], name: "index_ci_commits_on_status", using: :btree
   add_index "ci_commits", ["user_id"], name: "index_ci_commits_on_user_id", using: :btree
 
@@ -226,10 +216,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.datetime "updated_at"
   end
 
-  add_index "ci_events", ["created_at"], name: "index_ci_events_on_created_at", using: :btree
-  add_index "ci_events", ["is_admin"], name: "index_ci_events_on_is_admin", using: :btree
-  add_index "ci_events", ["project_id"], name: "index_ci_events_on_project_id", using: :btree
-
   create_table "ci_jobs", force: :cascade do |t|
     t.integer  "project_id",                          null: false
     t.text     "commands"
@@ -244,9 +230,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.datetime "deleted_at"
   end
 
-  add_index "ci_jobs", ["deleted_at"], name: "index_ci_jobs_on_deleted_at", using: :btree
-  add_index "ci_jobs", ["project_id"], name: "index_ci_jobs_on_project_id", using: :btree
-
   create_table "ci_projects", force: :cascade do |t|
     t.string   "name"
     t.integer  "timeout",                  default: 3600,  null: false
@@ -270,9 +253,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.text     "generated_yaml_config"
   end
 
-  add_index "ci_projects", ["gitlab_id"], name: "index_ci_projects_on_gitlab_id", using: :btree
-  add_index "ci_projects", ["shared_runners_enabled"], name: "index_ci_projects_on_shared_runners_enabled", using: :btree
-
   create_table "ci_runner_projects", force: :cascade do |t|
     t.integer  "runner_id",     null: false
     t.integer  "project_id"
@@ -314,8 +294,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.text     "properties"
   end
 
-  add_index "ci_services", ["project_id"], name: "index_ci_services_on_project_id", using: :btree
-
   create_table "ci_sessions", force: :cascade do |t|
     t.string   "session_id", null: false
     t.text     "data"
@@ -323,9 +301,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.datetime "updated_at"
   end
 
-  add_index "ci_sessions", ["session_id"], name: "index_ci_sessions_on_session_id", using: :btree
-  add_index "ci_sessions", ["updated_at"], name: "index_ci_sessions_on_updated_at", using: :btree
-
   create_table "ci_taggings", force: :cascade do |t|
     t.integer  "tag_id"
     t.integer  "taggable_id"
@@ -336,7 +311,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.datetime "created_at"
   end
 
-  add_index "ci_taggings", ["tag_id", "taggable_id", "taggable_type", "context", "tagger_id", "tagger_type"], name: "ci_taggings_idx", unique: true, using: :btree
   add_index "ci_taggings", ["taggable_id", "taggable_type", "context"], name: "index_ci_taggings_on_taggable_id_and_taggable_type_and_context", using: :btree
 
   create_table "ci_tags", force: :cascade do |t|
@@ -344,8 +318,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.integer "taggings_count", default: 0
   end
 
-  add_index "ci_tags", ["name"], name: "index_ci_tags_on_name", unique: true, using: :btree
-
   create_table "ci_trigger_requests", force: :cascade do |t|
     t.integer  "trigger_id", null: false
     t.text     "variables"
@@ -363,7 +335,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.integer  "gl_project_id"
   end
 
-  add_index "ci_triggers", ["deleted_at"], name: "index_ci_triggers_on_deleted_at", using: :btree
   add_index "ci_triggers", ["gl_project_id"], name: "index_ci_triggers_on_gl_project_id", using: :btree
 
   create_table "ci_variables", force: :cascade do |t|
@@ -469,7 +440,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.datetime "updated_at"
   end
 
-  add_index "identities", ["created_at", "id"], name: "index_identities_on_created_at_and_id", using: :btree
   add_index "identities", ["user_id"], name: "index_identities_on_user_id", using: :btree
 
   create_table "issues", force: :cascade do |t|
@@ -495,16 +465,13 @@ ActiveRecord::Schema.define(version: 20160810102349) do
   add_index "issues", ["assignee_id"], name: "index_issues_on_assignee_id", using: :btree
   add_index "issues", ["author_id"], name: "index_issues_on_author_id", using: :btree
   add_index "issues", ["confidential"], name: "index_issues_on_confidential", using: :btree
-  add_index "issues", ["created_at", "id"], name: "index_issues_on_created_at_and_id", using: :btree
   add_index "issues", ["created_at"], name: "index_issues_on_created_at", using: :btree
   add_index "issues", ["deleted_at"], name: "index_issues_on_deleted_at", using: :btree
   add_index "issues", ["description"], name: "index_issues_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
   add_index "issues", ["due_date"], name: "index_issues_on_due_date", using: :btree
   add_index "issues", ["milestone_id"], name: "index_issues_on_milestone_id", using: :btree
   add_index "issues", ["project_id", "iid"], name: "index_issues_on_project_id_and_iid", unique: true, using: :btree
-  add_index "issues", ["project_id"], name: "index_issues_on_project_id", using: :btree
   add_index "issues", ["state"], name: "index_issues_on_state", using: :btree
-  add_index "issues", ["title"], name: "index_issues_on_title", using: :btree
   add_index "issues", ["title"], name: "index_issues_on_title_trigram", using: :gin, opclasses: {"title"=>"gin_trgm_ops"}
 
   create_table "keys", force: :cascade do |t|
@@ -518,7 +485,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.boolean  "public",      default: false, null: false
   end
 
-  add_index "keys", ["created_at", "id"], name: "index_keys_on_created_at_and_id", using: :btree
   add_index "keys", ["fingerprint"], name: "index_keys_on_fingerprint", unique: true, using: :btree
   add_index "keys", ["user_id"], name: "index_keys_on_user_id", using: :btree
 
@@ -583,11 +549,9 @@ ActiveRecord::Schema.define(version: 20160810102349) do
   end
 
   add_index "members", ["access_level"], name: "index_members_on_access_level", using: :btree
-  add_index "members", ["created_at", "id"], name: "index_members_on_created_at_and_id", using: :btree
   add_index "members", ["invite_token"], name: "index_members_on_invite_token", unique: true, using: :btree
   add_index "members", ["requested_at"], name: "index_members_on_requested_at", using: :btree
   add_index "members", ["source_id", "source_type"], name: "index_members_on_source_id_and_source_type", using: :btree
-  add_index "members", ["type"], name: "index_members_on_type", using: :btree
   add_index "members", ["user_id"], name: "index_members_on_user_id", using: :btree
 
   create_table "merge_request_diffs", force: :cascade do |t|
@@ -634,7 +598,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
 
   add_index "merge_requests", ["assignee_id"], name: "index_merge_requests_on_assignee_id", using: :btree
   add_index "merge_requests", ["author_id"], name: "index_merge_requests_on_author_id", using: :btree
-  add_index "merge_requests", ["created_at", "id"], name: "index_merge_requests_on_created_at_and_id", using: :btree
   add_index "merge_requests", ["created_at"], name: "index_merge_requests_on_created_at", using: :btree
   add_index "merge_requests", ["deleted_at"], name: "index_merge_requests_on_deleted_at", using: :btree
   add_index "merge_requests", ["description"], name: "index_merge_requests_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
@@ -657,7 +620,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.integer  "iid"
   end
 
-  add_index "milestones", ["created_at", "id"], name: "index_milestones_on_created_at_and_id", using: :btree
   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
@@ -679,14 +641,13 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.boolean  "request_access_enabled", default: true,  null: false
   end
 
-  add_index "namespaces", ["created_at", "id"], name: "index_namespaces_on_created_at_and_id", using: :btree
+  add_index "namespaces", ["created_at"], name: "index_namespaces_on_created_at", using: :btree
   add_index "namespaces", ["name"], name: "index_namespaces_on_name", unique: true, using: :btree
   add_index "namespaces", ["name"], name: "index_namespaces_on_name_trigram", using: :gin, opclasses: {"name"=>"gin_trgm_ops"}
   add_index "namespaces", ["owner_id"], name: "index_namespaces_on_owner_id", using: :btree
   add_index "namespaces", ["path"], name: "index_namespaces_on_path", unique: true, using: :btree
   add_index "namespaces", ["path"], name: "index_namespaces_on_path_trigram", using: :gin, opclasses: {"path"=>"gin_trgm_ops"}
   add_index "namespaces", ["type"], name: "index_namespaces_on_type", using: :btree
-  add_index "namespaces", ["visibility_level"], name: "index_namespaces_on_visibility_level", using: :btree
 
   create_table "notes", force: :cascade do |t|
     t.text     "note"
@@ -709,7 +670,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
 
   add_index "notes", ["author_id"], name: "index_notes_on_author_id", using: :btree
   add_index "notes", ["commit_id"], name: "index_notes_on_commit_id", using: :btree
-  add_index "notes", ["created_at", "id"], name: "index_notes_on_created_at_and_id", using: :btree
   add_index "notes", ["created_at"], name: "index_notes_on_created_at", using: :btree
   add_index "notes", ["line_code"], name: "index_notes_on_line_code", using: :btree
   add_index "notes", ["note"], name: "index_notes_on_note_trigram", using: :gin, opclasses: {"note"=>"gin_trgm_ops"}
@@ -849,9 +809,8 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.boolean  "request_access_enabled",             default: true,      null: false
   end
 
-  add_index "projects", ["builds_enabled", "shared_runners_enabled"], name: "index_projects_on_builds_enabled_and_shared_runners_enabled", using: :btree
   add_index "projects", ["ci_id"], name: "index_projects_on_ci_id", using: :btree
-  add_index "projects", ["created_at", "id"], name: "index_projects_on_created_at_and_id", using: :btree
+  add_index "projects", ["created_at"], name: "index_projects_on_created_at", using: :btree
   add_index "projects", ["creator_id"], name: "index_projects_on_creator_id", using: :btree
   add_index "projects", ["description"], name: "index_projects_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
   add_index "projects", ["last_activity_at"], name: "index_projects_on_last_activity_at", using: :btree
@@ -937,9 +896,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.boolean  "wiki_page_events",      default: true
   end
 
-  add_index "services", ["category"], name: "index_services_on_category", using: :btree
-  add_index "services", ["created_at", "id"], name: "index_services_on_created_at_and_id", using: :btree
-  add_index "services", ["default"], name: "index_services_on_default", using: :btree
   add_index "services", ["project_id"], name: "index_services_on_project_id", using: :btree
   add_index "services", ["template"], name: "index_services_on_template", using: :btree
 
@@ -956,8 +912,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
   end
 
   add_index "snippets", ["author_id"], name: "index_snippets_on_author_id", using: :btree
-  add_index "snippets", ["created_at", "id"], name: "index_snippets_on_created_at_and_id", using: :btree
-  add_index "snippets", ["created_at"], name: "index_snippets_on_created_at", using: :btree
   add_index "snippets", ["file_name"], name: "index_snippets_on_file_name_trigram", using: :gin, opclasses: {"file_name"=>"gin_trgm_ops"}
   add_index "snippets", ["project_id"], name: "index_snippets_on_project_id", using: :btree
   add_index "snippets", ["title"], name: "index_snippets_on_title_trigram", using: :gin, opclasses: {"title"=>"gin_trgm_ops"}
@@ -1026,7 +980,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
   add_index "todos", ["commit_id"], name: "index_todos_on_commit_id", using: :btree
   add_index "todos", ["note_id"], name: "index_todos_on_note_id", using: :btree
   add_index "todos", ["project_id"], name: "index_todos_on_project_id", using: :btree
-  add_index "todos", ["state"], name: "index_todos_on_state", using: :btree
   add_index "todos", ["target_type", "target_id"], name: "index_todos_on_target_type_and_target_id", using: :btree
   add_index "todos", ["user_id"], name: "index_todos_on_user_id", using: :btree
 
@@ -1106,7 +1059,7 @@ ActiveRecord::Schema.define(version: 20160810102349) do
   add_index "users", ["admin"], name: "index_users_on_admin", using: :btree
   add_index "users", ["authentication_token"], name: "index_users_on_authentication_token", unique: true, using: :btree
   add_index "users", ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true, using: :btree
-  add_index "users", ["created_at", "id"], name: "index_users_on_created_at_and_id", using: :btree
+  add_index "users", ["created_at"], name: "index_users_on_created_at", using: :btree
   add_index "users", ["current_sign_in_at"], name: "index_users_on_current_sign_in_at", using: :btree
   add_index "users", ["email"], name: "index_users_on_email", unique: true, using: :btree
   add_index "users", ["email"], name: "index_users_on_email_trigram", using: :gin, opclasses: {"email"=>"gin_trgm_ops"}
@@ -1146,7 +1099,6 @@ ActiveRecord::Schema.define(version: 20160810102349) do
     t.string   "token"
   end
 
-  add_index "web_hooks", ["created_at", "id"], name: "index_web_hooks_on_created_at_and_id", using: :btree
   add_index "web_hooks", ["project_id"], name: "index_web_hooks_on_project_id", using: :btree
 
   add_foreign_key "personal_access_tokens", "users"