Add migration to swap ci_builds.stage_id column

Add new post-deployment migration that will cutover to the bigint
version of the ci_builds.stage_id column.

Changelog: changed

db/post_migrate/20210701141346_finalize_ci_builds_stage_id_bigint_conversion.rb

+# frozen_string_literal: true
+
+class FinalizeCiBuildsStageIdBigintConversion < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  TABLE_NAME = 'ci_builds'
+
+  def up
+    ensure_batched_background_migration_is_finished(
+      job_class_name: 'CopyColumnUsingBackgroundMigrationJob',
+      table_name: TABLE_NAME,
+      column_name: 'id',
+      job_arguments: [%w[id stage_id], %w[id_convert_to_bigint stage_id_convert_to_bigint]]
+    )
+
+    swap_columns
+  end
+
+  def down
+    swap_columns
+  end
+
+  private
+
+  def swap_columns
+    # Create a copy of the original column's index on the new column
+    add_concurrent_index TABLE_NAME, :stage_id_convert_to_bigint, name: :index_ci_builds_on_converted_stage_id # rubocop:disable Migration/PreventIndexCreation
+
+    # Create a copy of the original column's FK on the new column
+    add_concurrent_foreign_key TABLE_NAME, :ci_stages, column: :stage_id_convert_to_bigint, on_delete: :cascade,
+      reverse_lock_order: true
+
+    with_lock_retries(raise_on_exhaustion: true) do
+      quoted_table_name = quote_table_name(TABLE_NAME)
+      quoted_referenced_table_name = quote_table_name(:ci_stages)
+
+      # Acquire locks up-front, not just to the build table but the FK's referenced table
+      execute "LOCK TABLE #{quoted_referenced_table_name}, #{quoted_table_name} IN ACCESS EXCLUSIVE MODE"
+
+      # Swap the column names of the two columns
+      temporary_name = 'stage_id_tmp'
+      execute "ALTER TABLE #{quoted_table_name} RENAME COLUMN #{quote_column_name(:stage_id)} TO #{quote_column_name(temporary_name)}"
+      execute "ALTER TABLE #{quoted_table_name} RENAME COLUMN #{quote_column_name(:stage_id_convert_to_bigint)} TO #{quote_column_name(:stage_id)}"
+      execute "ALTER TABLE #{quoted_table_name} RENAME COLUMN #{quote_column_name(temporary_name)} TO #{quote_column_name(:stage_id_convert_to_bigint)}"
+
+      # Reset the function so PG drops the plan cache for the incorrect integer type
+      function_name = Gitlab::Database::UnidirectionalCopyTrigger.on_table(TABLE_NAME)
+        .name([:id, :stage_id], [:id_convert_to_bigint, :stage_id_convert_to_bigint])
+      execute "ALTER FUNCTION #{quote_table_name(function_name)} RESET ALL"
+
+      # Remove the original column index, and rename the new column index to the original name
+      execute 'DROP INDEX index_ci_builds_on_stage_id'
+      rename_index TABLE_NAME, :index_ci_builds_on_converted_stage_id, :index_ci_builds_on_stage_id
+
+      # Remove the original column foreign key, and rename the new column foreign key to the original name
+      remove_foreign_key TABLE_NAME, name: concurrent_foreign_key_name(TABLE_NAME, :stage_id)
+      rename_constraint(
+        TABLE_NAME,
+        concurrent_foreign_key_name(TABLE_NAME, :stage_id_convert_to_bigint),
+        concurrent_foreign_key_name(TABLE_NAME, :stage_id))
+    end
+  end
+end

db/schema_migrations/20210701141346

+da16754bf484ba9a585f9de055f242dbee311d7cf7d0ce67c834ebaed61b96d4
\ No newline at end of file

db/structure.sql

@@ -11371,7 +11371,7 @@ CREATE TABLE ci_builds (
     coverage_regex character varying,
     auto_canceled_by_id integer,
     retried boolean,
-    stage_id integer,
+    stage_id_convert_to_bigint integer,
     protected boolean,
     failure_reason integer,
     scheduled_at timestamp with time zone,
@@ -11382,7 +11382,7 @@ CREATE TABLE ci_builds (
     processed boolean,
     scheduling_type smallint,
     id_convert_to_bigint bigint DEFAULT 0 NOT NULL,
-    stage_id_convert_to_bigint bigint,
+    stage_id bigint,
     CONSTRAINT check_1e2fbd1b39 CHECK ((lock_version IS NOT NULL))
 );