Make IdsToBigints (mostly!) non-blocking (#5088)

* Make IdsToBigints (mostly!) non-blocking

This pulls in GitLab's MigrationHelpers, which include code to make
column changes in ways that Postgres can do without locking. In general,
this involves creating a new column, adding an index and any foreign
keys as appropriate, adding a trigger to keep it populated alongside
the old column, and then progressively copying data over to the new
column, before removing the old column and replacing it with the new
one.

A few changes to GitLab's MigrationHelpers were necessary:

* Some changes were made to remove dependencies on other GitLab code.
* We explicitly wait for index creation before forging ahead on column
  replacements.
* We use different temporary column names, to avoid running into index
  name length limits.
* We rename the generated indices back to what they "should" be after
  replacing columns.
* We rename the generated foreign keys to use the new column names when
  we had to create them. (This allows the migration to be rolled back
  without incident.)

# Big Scary Warning

There are two things here that may trip up large instances:

1. The change for tables' "id" columns is not concurrent. In
   particular, the stream_entries table may be big, and does not
   concurrently migrate its id column. (On the other hand, x_id type
   columns are all concurrent.)
2. This migration will take a long time to run, *but it should not
   lock tables during that time* (with the exception of the "id"
   columns as described above). That means this should probably be run
   in `screen` or some other session that can be run for a long time.
   Notably, the migration will take *longer* than it would without
   these changes, but the website will still be responsive during that
   time.

These changes were tested on a relatively large statuses table (256k
entries), and the service remained responsive during the migration.
Migrations both forward and backward were tested.

* Rubocop fixes

* MigrationHelpers: Support ID columns in some cases

This doesn't work in cases where the ID column is referred to as a
foreign key by another table.

* MigrationHelpers: support foreign keys for ID cols

Note that this does not yet support foreign keys on non-primary-key
columns, but Mastodon also doesn't yet have any that we've needed to
migrate.

This means we can perform fully "concurrent" migrations to change ID
column types, and the IdsToBigints migration can happen with effectively
no downtime. (A few operations require a transaction, such as renaming
columns or deleting them, but these transactions should not block for
noticeable amounts of time.)

The algorithm for generating foreign key names has changed with this,
and therefore all of those changed in schema.rb.

* Provide status, allow for interruptions

The MigrationHelpers now allow restarting the rename of a column if it
was interrupted, by removing the old "new column" and re-starting the
process.

Along with this, they now provide status updates on the changes which
are happening, as well as indications about when the changes can be
safely interrupted (when there are at least 10 seconds estimated to be
left before copying data is complete).

The IdsToBigints migration now also sorts the columns it migrates by
size, starting with the largest tables. This should provide
administrators a worst-case scenario estimate for the length of
migrations: each successive change will get faster, giving admins a
chance to abort early on if they need to run the migration later. The
idea is that this does not force them to try to time interruptions
between smaller migrations.

* Fix column sorting in IdsToBigints

Not a significant change, but it impacts the order of columns in the
database and db/schema.rb.

* Actually pause before IdsToBigints

15 files changed, 35 insertions, 36 deletions

diff --git a/app/models/account_domain_block.rb b/app/models/account_domain_block.rb
index bdd64c01a..fb695e473 100644
--- a/app/models/account_domain_block.rb
+++ b/app/models/account_domain_block.rb
@@ -3,11 +3,11 @@
 #
 # Table name: account_domain_blocks
 #
-#  id         :integer          not null, primary key
-#  account_id :integer
 #  domain     :string
 #  created_at :datetime         not null
 #  updated_at :datetime         not null
+#  account_id :integer
+#  id         :integer          not null, primary key
 #
 
 class AccountDomainBlock < ApplicationRecord
diff --git a/app/models/block.rb b/app/models/block.rb
index edb0d2d11..a913782ed 100644
--- a/app/models/block.rb
+++ b/app/models/block.rb
@@ -3,11 +3,11 @@
 #
 # Table name: blocks
 #
-#  id                :integer          not null, primary key
-#  account_id        :integer          not null
-#  target_account_id :integer          not null
 #  created_at        :datetime         not null
 #  updated_at        :datetime         not null
+#  account_id        :integer          not null
+#  id                :integer          not null, primary key
+#  target_account_id :integer          not null
 #
 
 class Block < ApplicationRecord
diff --git a/app/models/conversation_mute.rb b/app/models/conversation_mute.rb
index 79299b995..8d2399adf 100644
--- a/app/models/conversation_mute.rb
+++ b/app/models/conversation_mute.rb
@@ -3,9 +3,9 @@
 #
 # Table name: conversation_mutes
 #
-#  id              :integer          not null, primary key
-#  account_id      :integer          not null
 #  conversation_id :integer          not null
+#  account_id      :integer          not null
+#  id              :integer          not null, primary key
 #
 
 class ConversationMute < ApplicationRecord
diff --git a/app/models/domain_block.rb b/app/models/domain_block.rb
index aea8919af..1268290bc 100644
--- a/app/models/domain_block.rb
+++ b/app/models/domain_block.rb
@@ -3,12 +3,12 @@
 #
 # Table name: domain_blocks
 #
-#  id           :integer          not null, primary key
 #  domain       :string           default(""), not null
 #  created_at   :datetime         not null
 #  updated_at   :datetime         not null
 #  severity     :integer          default("silence")
 #  reject_media :boolean          default(FALSE), not null
+#  id           :integer          not null, primary key
 #
 
 class DomainBlock < ApplicationRecord
diff --git a/app/models/favourite.rb b/app/models/favourite.rb
index 53c79ccea..d28d5c05b 100644
--- a/app/models/favourite.rb
+++ b/app/models/favourite.rb
@@ -3,11 +3,11 @@
 #
 # Table name: favourites
 #
-#  id         :integer          not null, primary key
-#  account_id :integer          not null
-#  status_id  :integer          not null
 #  created_at :datetime         not null
 #  updated_at :datetime         not null
+#  account_id :integer          not null
+#  id         :integer          not null, primary key
+#  status_id  :integer          not null
 #
 
 class Favourite < ApplicationRecord
diff --git a/app/models/follow.rb b/app/models/follow.rb
index 62f6fb670..667720a88 100644
--- a/app/models/follow.rb
+++ b/app/models/follow.rb
@@ -3,11 +3,11 @@
 #
 # Table name: follows
 #
-#  id                :integer          not null, primary key
-#  account_id        :integer          not null
-#  target_account_id :integer          not null
 #  created_at        :datetime         not null
 #  updated_at        :datetime         not null
+#  account_id        :integer          not null
+#  id                :integer          not null, primary key
+#  target_account_id :integer          not null
 #
 
 class Follow < ApplicationRecord
diff --git a/app/models/follow_request.rb b/app/models/follow_request.rb
index 458c3a2cd..60036d903 100644
--- a/app/models/follow_request.rb
+++ b/app/models/follow_request.rb
@@ -3,11 +3,11 @@
 #
 # Table name: follow_requests
 #
-#  id                :integer          not null, primary key
-#  account_id        :integer          not null
-#  target_account_id :integer          not null
 #  created_at        :datetime         not null
 #  updated_at        :datetime         not null
+#  account_id        :integer          not null
+#  id                :integer          not null, primary key
+#  target_account_id :integer          not null
 #
 
 class FollowRequest < ApplicationRecord
diff --git a/app/models/import.rb b/app/models/import.rb
index 4656c3af6..8ae7e3a46 100644
--- a/app/models/import.rb
+++ b/app/models/import.rb
@@ -3,8 +3,6 @@
 #
 # Table name: imports
 #
-#  id                :integer          not null, primary key
-#  account_id        :integer          not null
 #  type              :integer          not null
 #  approved          :boolean          default(FALSE), not null
 #  created_at        :datetime         not null
@@ -13,6 +11,8 @@
 #  data_content_type :string
 #  data_file_size    :integer
 #  data_updated_at   :datetime
+#  account_id        :integer          not null
+#  id                :integer          not null, primary key
 #
 
 class Import < ApplicationRecord
diff --git a/app/models/mention.rb b/app/models/mention.rb
index 7450b1b85..3700c781c 100644
--- a/app/models/mention.rb
+++ b/app/models/mention.rb
@@ -3,11 +3,11 @@
 #
 # Table name: mentions
 #
-#  id         :integer          not null, primary key
-#  account_id :integer
 #  status_id  :integer
 #  created_at :datetime         not null
 #  updated_at :datetime         not null
+#  account_id :integer
+#  id         :integer          not null, primary key
 #
 
 class Mention < ApplicationRecord
diff --git a/app/models/mute.rb b/app/models/mute.rb
index 00e5661a7..6e64848c7 100644
--- a/app/models/mute.rb
+++ b/app/models/mute.rb
@@ -3,11 +3,11 @@
 #
 # Table name: mutes
 #
-#  id                :integer          not null, primary key
-#  account_id        :integer          not null
-#  target_account_id :integer          not null
 #  created_at        :datetime         not null
 #  updated_at        :datetime         not null
+#  account_id        :integer          not null
+#  id                :integer          not null, primary key
+#  target_account_id :integer          not null
 #
 
 class Mute < ApplicationRecord
diff --git a/app/models/report.rb b/app/models/report.rb
index 479aa17bb..bffb42b48 100644
--- a/app/models/report.rb
+++ b/app/models/report.rb
@@ -3,15 +3,15 @@
 #
 # Table name: reports
 #
-#  id                         :integer          not null, primary key
-#  account_id                 :integer          not null
-#  target_account_id          :integer          not null
 #  status_ids                 :integer          default([]), not null, is an Array
 #  comment                    :text             default(""), not null
 #  action_taken               :boolean          default(FALSE), not null
 #  created_at                 :datetime         not null
 #  updated_at                 :datetime         not null
+#  account_id                 :integer          not null
 #  action_taken_by_account_id :integer
+#  id                         :integer          not null, primary key
+#  target_account_id          :integer          not null
 #
 
 class Report < ApplicationRecord
diff --git a/app/models/setting.rb b/app/models/setting.rb
index 340552581..a14f156a1 100644
--- a/app/models/setting.rb
+++ b/app/models/setting.rb
@@ -3,13 +3,13 @@
 #
 # Table name: settings
 #
-#  id         :integer          not null, primary key
 #  var        :string           not null
 #  value      :text
 #  thing_type :string
-#  thing_id   :integer
 #  created_at :datetime
 #  updated_at :datetime
+#  id         :integer          not null, primary key
+#  thing_id   :integer
 #
 
 class Setting < RailsSettings::Base
diff --git a/app/models/stream_entry.rb b/app/models/stream_entry.rb
index 44aac39b3..b51fe9ad7 100644
--- a/app/models/stream_entry.rb
+++ b/app/models/stream_entry.rb
@@ -1,16 +1,15 @@
 # frozen_string_literal: true
-
 # == Schema Information
 #
 # Table name: stream_entries
 #
-#  id            :integer          not null, primary key
-#  account_id    :integer
 #  activity_id   :integer
 #  activity_type :string
 #  created_at    :datetime         not null
 #  updated_at    :datetime         not null
 #  hidden        :boolean          default(FALSE), not null
+#  account_id    :integer
+#  id            :integer          not null, primary key
 #
 
 class StreamEntry < ApplicationRecord
diff --git a/app/models/subscription.rb b/app/models/subscription.rb
index 14f1a140c..39860196b 100644
--- a/app/models/subscription.rb
+++ b/app/models/subscription.rb
@@ -3,16 +3,16 @@
 #
 # Table name: subscriptions
 #
-#  id                          :integer          not null, primary key
 #  callback_url                :string           default(""), not null
 #  secret                      :string
 #  expires_at                  :datetime
 #  confirmed                   :boolean          default(FALSE), not null
-#  account_id                  :integer          not null
 #  created_at                  :datetime         not null
 #  updated_at                  :datetime         not null
 #  last_successful_delivery_at :datetime
 #  domain                      :string
+#  account_id                  :integer          not null
+#  id                          :integer          not null, primary key
 #
 
 class Subscription < ApplicationRecord
diff --git a/app/models/web/setting.rb b/app/models/web/setting.rb
index 04a049523..1b0bfb2b7 100644
--- a/app/models/web/setting.rb
+++ b/app/models/web/setting.rb
@@ -3,11 +3,11 @@
 #
 # Table name: web_settings
 #
-#  id         :integer          not null, primary key
-#  user_id    :integer
 #  data       :json
 #  created_at :datetime         not null
 #  updated_at :datetime         not null
+#  id         :integer          not null, primary key
+#  user_id    :integer
 #
 
 class Web::Setting < ApplicationRecord