Remove AddIndexToCiBuildsArtifactsFile. Add temporary index in background migration class.

db/migrate/20180428200509_add_index_to_ci_builds_artifacts_file.rb

-class AddIndexToCiBuildsArtifactsFile < ActiveRecord::Migration
-  include Gitlab::Database::MigrationHelpers
-
-  DOWNTIME = false
-
-  disable_ddl_transaction!
-
-  def up
-    # We add an temporary index to `ci_builds.artifacts_file` column to avoid statements timeout in legacy artifacts migrations
-    # This index is to be removed after we have cleaned up background migrations
-    # https://gitlab.com/gitlab-org/gitlab-ce/issues/46866
-    if Gitlab::Database.postgresql?
-      add_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''"
-    elsif Gitlab::Database.mysql?
-      add_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''", length: 20
-    end
-  end
-
-  def down
-    if Gitlab::Database.postgresql?
-      remove_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''"
-    elsif Gitlab::Database.mysql?
-      remove_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''", length: 20
-    end
-  end
-end

db/post_migrate/20180430161409_migrate_legacy_artifacts_to_job_artifacts.rb

@@ -4,10 +4,28 @@ class MigrateLegacyArtifactsToJobArtifacts < ActiveRecord::Migration
   DOWNTIME = false
   MIGRATION = 'MigrateLegacyArtifacts'.freeze
   BATCH_SIZE = 2000
-
+  TMP_INDEX = 'tmp_index_ci_builds_on_present_artifacts_file'.freeze
+  
   disable_ddl_transaction!
 
   def up
+    ##
+    # We add a temporary index to `artifacts_file`. Without having this,
+    # queries generated by `each_batch` by statement timeout.
+    #
+    # This is only neccessary when we collect target rows, because in backgroun migrartions
+    # it's filitered by `BETWEEN` clause (e.g. 'id BETWEEN 0 AND 2000'), so it's fast enough without this temporary index.
+    #
+    # Mysql doesn't support partial indexies. Also, it requires the index to specify `length` only if the type is `TEXT`, `VARCHAR`, etc.
+    # Therefore we need to treat this id generation differently by database type.
+    unless index_exists_by_name?(:ci_builds, TMP_INDEX)
+      if Gitlab::Database.postgresql?
+        add_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''", name: TMP_INDEX
+      elsif Gitlab::Database.mysql?
+        add_concurrent_index :ci_builds, :artifacts_file, length: 20, name: TMP_INDEX
+      end
+    end
+
     ::Gitlab::BackgroundMigration::MigrateLegacyArtifacts::Build
       .with_legacy_artifacts.without_new_artifacts.tap do |relation|
       queue_background_migration_jobs_by_range_at_intervals(relation,
@@ -15,9 +33,13 @@ class MigrateLegacyArtifactsToJobArtifacts < ActiveRecord::Migration
                                                             5.minutes,
                                                             batch_size: BATCH_SIZE)
     end
+
+    remove_concurrent_index_by_name(:ci_builds, TMP_INDEX)
   end
 
   def down
-    # no-op
+    if index_exists_by_name?(:ci_builds, TMP_INDEX)
+      remove_concurrent_index_by_name(:ci_builds, TMP_INDEX)
+    end
   end
 end

db/schema.rb

@@ -331,7 +331,6 @@ 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)", length: 20, 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
@@ -1233,7 +1232,6 @@ ActiveRecord::Schema.define(version: 20180603190921) do
     t.integer "latest_merge_request_diff_id"
     t.string "rebase_commit_sha"
     t.boolean "allow_collaboration"
-    t.boolean "squash", default: false, null: false
   end
 
   add_index "merge_requests", ["assignee_id"], name: "index_merge_requests_on_assignee_id", using: :btree