Merge branch 'remove-ci-runner-trigram-indexes' into 'master'

Remove trigram indexes for "ci_runners"

## What does this MR do?

This MR removes two trigram indexes from the `ci_runners` table.

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

No.

## Why was this MR needed?

These indexes are only very rarely used while slowing down any update. See 4baee5d3a2e9e3b49a991db89e335072b911e64c for more information.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [x] ~~API support added~~
- Tests
  - [x] ~~Added for this feature/bug~~
  - [ ] All builds are passing
- [x ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] 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 !5755

CHANGELOG

@@ -39,6 +39,7 @@ v 8.11.0 (unreleased)
   - Retrieve rendered HTML from cache in one request
   - Fix renaming repository when name contains invalid chararacters under project settings
   - Upgrade Grape from 0.13.0 to 0.15.0. !4601
+  - Trigram indexes for the "ci_runners" table have been removed to speed up UPDATE queries
   - Fix devise deprecation warnings.
   - Update version_sorter and use new interface for faster tag sorting
   - Optimize checking if a user has read access to a list of issues !5370

db/migrate/20160810102349_remove_ci_runner_trigram_indexes.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveCiRunnerTrigramIndexes < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  # Disabled for the "down" method so the indexes can be re-created concurrently.
+  disable_ddl_transaction!
+
+  def up
+    return unless Gitlab::Database.postgresql?
+
+    transaction do
+      execute 'DROP INDEX IF EXISTS index_ci_runners_on_token_trigram;'
+      execute 'DROP INDEX IF EXISTS index_ci_runners_on_description_trigram;'
+    end
+  end
+
+  def down
+    return unless Gitlab::Database.postgresql?
+
+    execute 'CREATE INDEX CONCURRENTLY index_ci_runners_on_token_trigram ON ci_runners USING gin(token gin_trgm_ops);'
+    execute 'CREATE INDEX CONCURRENTLY index_ci_runners_on_description_trigram ON ci_runners USING gin(description gin_trgm_ops);'
+  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: 20160804150737) do
+ActiveRecord::Schema.define(version: 20160810102349) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -301,10 +301,8 @@ ActiveRecord::Schema.define(version: 20160804150737) do
     t.boolean  "locked",       default: false, null: false
   end
 
-  add_index "ci_runners", ["description"], name: "index_ci_runners_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
   add_index "ci_runners", ["locked"], name: "index_ci_runners_on_locked", using: :btree
   add_index "ci_runners", ["token"], name: "index_ci_runners_on_token", using: :btree
-  add_index "ci_runners", ["token"], name: "index_ci_runners_on_token_trigram", using: :gin, opclasses: {"token"=>"gin_trgm_ops"}
 
   create_table "ci_services", force: :cascade do |t|
     t.string   "type"