diff --git a/Gemfile b/Gemfile
index 9236d99478e..4cc989816b0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -113,6 +113,9 @@ gem 'kgio', '2.10.0'
 # TODO: AO3-6297 Update the download code so we can remove mimemagic.
 gem "mimemagic", "0.3.10"
 
+# Library for helping run pt-online-schema-change commands:
+gem "departure", "~> 6.5"
+
 group :test do
   gem "rspec-rails", "~> 4.0.1"
   gem 'pickle'
diff --git a/Gemfile.lock b/Gemfile.lock
index 420e80799d3..4959418eebd 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -205,6 +205,10 @@ GEM
     database_cleaner-core (2.0.1)
     delorean (2.1.0)
       chronic
+    departure (6.5.0)
+      activerecord (>= 5.2.0, < 7.1, != 7.0.0)
+      mysql2 (>= 0.4.0, <= 0.5.5)
+      railties (>= 5.2.0, < 7.1, != 7.0.0)
     devise (4.8.1)
       bcrypt (~> 3.0)
       orm_adapter (~> 0.1)
@@ -624,6 +628,7 @@ DEPENDENCIES
   dalli
   database_cleaner
   delorean
+  departure (~> 6.5)
   devise
   devise-async
   elasticsearch (= 7.17.1)
diff --git a/config/config.yml b/config/config.yml
index 6625b10062e..e52da538648 100644
--- a/config/config.yml
+++ b/config/config.yml
@@ -518,3 +518,14 @@ WRANGLING_REPORT_LIMIT: 1000
 # After this window, all comments are disabled. Setting this value to
 # something below 1 -- or commenting it out -- will turn off comment disabling.
 ADMIN_POST_COMMENTING_EXPIRATION_DAYS: 14
+
+# The arguments to pass to pt-online-schema-change:
+PERCONA_ARGS: >
+  --chunk-size=5k
+  --max-flow-ctl 0
+  --pause-file /tmp/pauseme
+  --max-load Threads_running=15
+  --critical-load Threads_running=100
+  --set-vars innodb_lock_wait_timeout=2
+  --alter-foreign-keys-method=auto
+  --no-check-unique-key-change
diff --git a/config/initializers/departure.rb b/config/initializers/departure.rb
new file mode 100644
index 00000000000..f201a5630d4
--- /dev/null
+++ b/config/initializers/departure.rb
@@ -0,0 +1,10 @@
+Departure.configure do |config|
+  # Disable departure by default. To use pt-online-schema-change for a
+  # migration, call
+  #     uses_departure! if Rails.env.staging? || Rails.env.production?
+  # in the migration file.
+  config.enabled_by_default = false
+
+  # Set the arguments based on the config file:
+  config.global_percona_args = ArchiveConfig.PERCONA_ARGS.squish
+end
diff --git a/db/migrate/20230610162442_add_indices_to_tag_set_associations.rb b/db/migrate/20230610162442_add_indices_to_tag_set_associations.rb
new file mode 100644
index 00000000000..be9ff0658a9
--- /dev/null
+++ b/db/migrate/20230610162442_add_indices_to_tag_set_associations.rb
@@ -0,0 +1,14 @@
+class AddIndicesToTagSetAssociations < ActiveRecord::Migration[6.1]
+  uses_departure! if Rails.env.staging? || Rails.env.production?
+
+  def change
+    change_table :tag_set_associations do |t|
+      t.index :tag_id
+      t.index :parent_tag_id
+
+      t.index [:owned_tag_set_id, :parent_tag_id, :tag_id],
+              name: :index_tag_set_associations_on_tag_set_and_parent_and_tag,
+              unique: true
+    end
+  end
+end