Drop id column in ci_build_trace_sections table

This commit drops the id column of the `ci_build_trace_sections`
table, which is about to overflow.

changelogs/unreleased/drop-id-of-ci-trace-sectinos.yml

+---
+title: Drop `id` column from `ci_build_trace_sections` table
+merge_request: 18741
+author:
+type: changed

db/post_migrate/20191017180026_drop_ci_build_trace_sections_id.rb

+# frozen_string_literal: true
+
+class DropCiBuildTraceSectionsId < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def up
+    ##
+    # This column has already been ignored since 12.4
+    # See https://gitlab.com/gitlab-org/gitlab/issues/32569
+    remove_column :ci_build_trace_sections, :id
+  end
+
+  def down
+    ##
+    # We don't backfill serial ids as it's not used in application code
+    # and quite expensive process.
+    add_column :ci_build_trace_sections, :id, :bigint
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_10_17_094449) do
+ActiveRecord::Schema.define(version: 2019_10_17_180026) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -599,7 +599,7 @@ ActiveRecord::Schema.define(version: 2019_10_17_094449) do
     t.index ["project_id", "name"], name: "index_ci_build_trace_section_names_on_project_id_and_name", unique: true
   end
 
-  create_table "ci_build_trace_sections", id: :serial, force: :cascade do |t|
+  create_table "ci_build_trace_sections", id: false, force: :cascade do |t|
     t.integer "project_id", null: false
     t.datetime "date_start", null: false
     t.datetime "date_end", null: false