Add temporary index to ci_builds.artifacts_file to speed up SELECT query

db/migrate/20180427160409_add_legacy_path_to_ci_job_artifacts.rb → db/migrate/20180427160409_add_file_location_to_ci_job_artifacts.rb

-class AddLegacyPathToCiJobArtifacts < ActiveRecord::Migration
+class AddFileLocationToCiJobArtifacts < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
   DOWNTIME = false

db/post_migrate/20180427161409_migrate_legacy_artifacts_to_job_artifacts.rb

@@ -3,7 +3,7 @@ class MigrateLegacyArtifactsToJobArtifacts < ActiveRecord::Migration
   DOWNTIME = false
   MIGRATION = 'MigrateLegacyArtifacts'.freeze
-  BATCH_SIZE = 500
+  BATCH_SIZE = 2000
   disable_ddl_transaction!
@@ -30,7 +30,12 @@ class MigrateLegacyArtifactsToJobArtifacts < ActiveRecord::Migration
   end
   def up
-    disable_statement_timeout
+    # We add an temporary index to `ci_builds.artifacts_file` column to avoid statements timeout
+    # This index is to be removed after we have cleaned up background migrations
+    # https://gitlab.com/gitlab-org/gitlab-ce/issues/46866
+    unless index_exists?(:ci_builds, :artifacts_file)
+      add_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''"
+    end
     MigrateLegacyArtifactsToJobArtifacts::Build.legacy_artifacts.without_new_artifacts.tap do |relation|
       queue_background_migration_jobs_by_range_at_intervals(relation,
@@ -41,6 +46,8 @@ class MigrateLegacyArtifactsToJobArtifacts < ActiveRecord::Migration
   end
   def down
-    # There's nothing to revert for this migration.
+    if index_exists?(:ci_builds, :artifacts_file)
+      remove_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''"
+    end
   end
 end

db/schema.rb

@@ -331,6 +331,7 @@ ActiveRecord::Schema.define(version: 20180603190921) do
   end
   add_index "ci_builds", ["artifacts_expire_at"], name: "index_ci_builds_on_artifacts_expire_at", where: "(artifacts_file <> ''::text)", using: :btree
+  add_index "ci_builds", ["artifacts_file"], name: "index_ci_builds_on_artifacts_file", where: "(artifacts_file <> ''::text)", using: :btree
   add_index "ci_builds", ["auto_canceled_by_id"], name: "index_ci_builds_on_auto_canceled_by_id", using: :btree
   add_index "ci_builds", ["commit_id", "stage_idx", "created_at"], name: "index_ci_builds_on_commit_id_and_stage_idx_and_created_at", using: :btree
   add_index "ci_builds", ["commit_id", "status", "type"], name: "index_ci_builds_on_commit_id_and_status_and_type", using: :btree