Added trigram indexes for various searched columns

This allows the LIKE condition to use an index. Without a GIN + trigram
index LIKE queries using a wildcard at the start _won't_ use an index
and instead perform a sequence scan.

db/migrate/20160226114608_add_trigram_indexes_for_searching.rb

+class AddTrigramIndexesForSearching < ActiveRecord::Migration
+  disable_ddl_transaction!
+
+  def up
+    return unless Gitlab::Database.postgresql?
+
+    unless trigrams_enabled?
+      raise 'You must enable the pg_trgm extension as a PostgreSQL super user'
+    end
+
+    # trigram indexes are case-insensitive so we can just index the column
+    # instead of indexing lower(column)
+    to_index.each do |table, columns|
+      columns.each do |column|
+        execute "CREATE INDEX CONCURRENTLY index_#{table}_on_#{column}_trigram ON #{table} USING gin(#{column} gin_trgm_ops);"
+      end
+    end
+  end
+
+  def down
+    return unless Gitlab::Database.postgresql?
+
+    to_index.each do |table, columns|
+      columns.each do |column|
+        remove_index table, name: "index_#{table}_on_#{column}_trigram"
+      end
+    end
+  end
+
+  def trigrams_enabled?
+    res = execute("SELECT true AS enabled FROM pg_available_extensions WHERE name = 'pg_trgm' AND installed_version IS NOT NULL;")
+    row = res.first
+
+    row && row['enabled'] == 't' ? true : false
+  end
+
+  def to_index
+    {
+      ci_runners:     [:token, :description],
+      issues:         [:title, :description],
+      merge_requests: [:title, :description],
+      milestones:     [:title, :description],
+      namespaces:     [:name, :path],
+      notes:          [:note],
+      projects:       [:name, :path, :description],
+      snippets:       [:title, :file_name],
+      users:          [:username, :name, :email]
+    }
+  end
+end

db/schema.rb

@@ -15,6 +15,7 @@ ActiveRecord::Schema.define(version: 20160309140734) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
+  enable_extension "pg_trgm"
 
   create_table "abuse_reports", force: :cascade do |t|
     t.integer  "reporter_id"
@@ -258,6 +259,9 @@ ActiveRecord::Schema.define(version: 20160309140734) do
     t.string   "architecture"
   end
 
+  add_index "ci_runners", ["description"], name: "index_ci_runners_on_description_trigram", using: :gin
+  add_index "ci_runners", ["token"], name: "index_ci_runners_on_token_trigram", using: :gin
+
   create_table "ci_services", force: :cascade do |t|
     t.string   "type"
     t.string   "title"
@@ -417,11 +421,13 @@ ActiveRecord::Schema.define(version: 20160309140734) do
   add_index "issues", ["author_id"], name: "index_issues_on_author_id", 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", ["description"], name: "index_issues_on_description_trigram", using: :gin
   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
 
   create_table "keys", force: :cascade do |t|
     t.integer  "user_id"
@@ -543,12 +549,14 @@ ActiveRecord::Schema.define(version: 20160309140734) do
   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", ["description"], name: "index_merge_requests_on_description_trigram", using: :gin
   add_index "merge_requests", ["milestone_id"], name: "index_merge_requests_on_milestone_id", using: :btree
   add_index "merge_requests", ["source_branch"], name: "index_merge_requests_on_source_branch", using: :btree
   add_index "merge_requests", ["source_project_id"], name: "index_merge_requests_on_source_project_id", using: :btree
   add_index "merge_requests", ["target_branch"], name: "index_merge_requests_on_target_branch", using: :btree
   add_index "merge_requests", ["target_project_id", "iid"], name: "index_merge_requests_on_target_project_id_and_iid", unique: true, using: :btree
   add_index "merge_requests", ["title"], name: "index_merge_requests_on_title", using: :btree
+  add_index "merge_requests", ["title"], name: "index_merge_requests_on_title_trigram", using: :gin
 
   create_table "milestones", force: :cascade do |t|
     t.string   "title",       null: false
@@ -562,10 +570,12 @@ ActiveRecord::Schema.define(version: 20160309140734) do
   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
   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
 
   create_table "namespaces", force: :cascade do |t|
     t.string   "name",                     null: false
@@ -580,8 +590,10 @@ ActiveRecord::Schema.define(version: 20160309140734) do
 
   add_index "namespaces", ["created_at", "id"], name: "index_namespaces_on_created_at_and_id", 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
   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
   add_index "namespaces", ["type"], name: "index_namespaces_on_type", using: :btree
 
   create_table "notes", force: :cascade do |t|
@@ -607,6 +619,7 @@ ActiveRecord::Schema.define(version: 20160309140734) do
   add_index "notes", ["created_at"], name: "index_notes_on_created_at", using: :btree
   add_index "notes", ["is_award"], name: "index_notes_on_is_award", 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
   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
@@ -705,9 +718,12 @@ ActiveRecord::Schema.define(version: 20160309140734) do
   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", ["creator_id"], name: "index_projects_on_creator_id", using: :btree
+  add_index "projects", ["description"], name: "index_projects_on_description_trigram", using: :gin
   add_index "projects", ["last_activity_at"], name: "index_projects_on_last_activity_at", using: :btree
+  add_index "projects", ["name"], name: "index_projects_on_name_trigram", using: :gin
   add_index "projects", ["namespace_id"], name: "index_projects_on_namespace_id", using: :btree
   add_index "projects", ["path"], name: "index_projects_on_path", using: :btree
+  add_index "projects", ["path"], name: "index_projects_on_path_trigram", using: :gin
   add_index "projects", ["runners_token"], name: "index_projects_on_runners_token", using: :btree
   add_index "projects", ["star_count"], name: "index_projects_on_star_count", using: :btree
   add_index "projects", ["visibility_level"], name: "index_projects_on_visibility_level", using: :btree
@@ -785,7 +801,9 @@ ActiveRecord::Schema.define(version: 20160309140734) do
   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
   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
   add_index "snippets", ["updated_at"], name: "index_snippets_on_updated_at", using: :btree
   add_index "snippets", ["visibility_level"], name: "index_snippets_on_visibility_level", using: :btree
 
@@ -919,9 +937,12 @@ ActiveRecord::Schema.define(version: 20160309140734) do
   add_index "users", ["created_at", "id"], name: "index_users_on_created_at_and_id", 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
   add_index "users", ["name"], name: "index_users_on_name", using: :btree
+  add_index "users", ["name"], name: "index_users_on_name_trigram", using: :gin
   add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree
   add_index "users", ["username"], name: "index_users_on_username", using: :btree
+  add_index "users", ["username"], name: "index_users_on_username_trigram", using: :gin
 
   create_table "users_star_projects", force: :cascade do |t|
     t.integer  "project_id", null: false