Specify length of index in schema.rb manually for resolving mysql errors

db/migrate/20180428200509_add_index_to_ci_builds_artifacts_file.rb

@@ -9,11 +9,7 @@ class AddIndexToCiBuildsArtifactsFile < ActiveRecord::Migration
     # 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.mysql?
-      add_concurrent_index :ci_builds, :artifacts_file, length: 65535 - 1
-    else
-      add_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''"
-    end
+    add_concurrent_index :ci_builds, :artifacts_file, where: "artifacts_file <> ''", length: 20
   end
 
   def down

db/schema.rb

@@ -331,7 +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", ["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