Rollwire

Rollwire detects ActiveRecord::Rollback exceptions that Rails silently ignores when a nested transaction joins its parent without creating a savepoint.

The problem

Both records are committed in this example:

User.transaction do
  User.create!(name: "Kotori")

  User.transaction do
    User.create!(name: "Nemu")
    raise ActiveRecord::Rollback
  end
end

The inner call joins the existing transaction. Rails catches ActiveRecord::Rollback, but there is no savepoint to roll back and the exception does not reach the outer block. This is documented behavior in Active Record transactions.

Rollwire reports this only when the joined block executes a write (INSERT, UPDATE, DELETE, or SELECT ... FOR UPDATE) before raising the rollback.

Installation

Until version 0.1.0 is published on RubyGems, install from the repository:

gem "rollwire", github: "ydah/rollwire"

Then run:

bundle install

The gem installs its Active Record patches when required.

Configuration

Add an initializer:

Rollwire.configure do |config|
  config.mode = :raise
  config.min_writes = 1
  config.count_writes = true
  config.capture_outer_location = true
  config.backtrace_lines = 10
  config.strict_patching = false
  config.ignore_if = nil
end

The Railtie defaults to :raise in test and :log in other Rails environments. Setting mode explicitly overrides the environment default.

Setting	Default	Purpose
mode	:raise in test, otherwise :log	Select reporting behavior
min_writes	1	Minimum matching SQL statements before reporting
count_writes	true	Disable to report even when no write was observed
capture_outer_location	true	Record the real outer transaction location
backtrace_lines	10	Control the amount of stack inspected for locations
strict_patching	false	Raise instead of warning and disabling on an incompatible Active Record API
ignore_if	nil	Callable that suppresses selected reports

Modes

• :log writes the report to Rails.logger (or stderr). It re-raises the original rollback inside Rails, so application behavior and final database state remain unchanged.
• :notify emits ignored_rollback.rollwire with the report in payload[:report]. Database behavior is unchanged.
• :raise replaces the ignored rollback with Rollwire::IgnoredNestedRollback. This escapes the joined block and rolls back the outer transaction.

:raise is intentionally test-only: it changes the final database state. In the opening example, :log and :notify leave both Kotori and Nemu committed; :raise leaves neither record committed.

Subscribe to notification mode with:

ActiveSupport::Notifications.subscribe(
  "ignored_rollback.rollwire"
) do |*, payload|
  report = payload.fetch(:report)
  ErrorTracker.notify(report.to_s)
end

Suppression

Suppress a known-safe region:

Rollwire.suppress do
  LegacyImporter.call
end

Or ignore reports selectively:

Rollwire.configure do |config|
  config.ignore_if = lambda do |report|
    report.inner_location&.include?("lib/legacy/")
  end
end

Rollwire.disable! and Rollwire.enable! disable or enable detection globally.

Transactional tests and fixtures

Rails transactional tests use a non-joinable outer transaction. This creates an important difference from production:

• An application transaction directly inside the test transaction gets a savepoint. Its rollback works, so there is no ignored rollback for this gem to detect—even if the same single application transaction would be unsafe in production.
• With two application transaction levels (service A calls service B), the first application transaction is a joinable savepoint and the second joins it. Rollwire detects a rollback in the second level.

Installing this gem therefore does not make a single-transaction fixture test prove production behavior. It detects the problem only on execution paths where a joined nested transaction actually occurs.

Reports and safety

A log report identifies the inner and real outer transaction call sites:

Rollwire::IgnoredNestedRollback

ActiveRecord::Rollback was raised inside a transaction
that joined an existing transaction.

The 2 writes executed inside this block will not be rolled back.

Inner transaction:
  app/services/create_user.rb:24

Outer transaction:
  app/services/import_users.rb:61

Use `requires_new: true` to roll back only the inner block,
or propagate the failure to the outer transaction.

Write frames are isolated by Active Support execution context and database connection. SQL classification uses the payload SQL, not its event name, so update_columns and raw execute writes are included.

Reporting failures are converted to warnings. Other than the dedicated exception in :raise mode, instrumentation errors do not replace the original rollback or change transaction behavior.

Isolator

Isolator detects non-atomic side effects and can limit nested transaction depth. Rollwire has a narrower purpose: it detects a rollback that was specifically ignored because a nested Active Record transaction joined its parent. The gems are complementary.

Compatibility

The CI support matrix is:

Ruby	Active Record 7.1	Active Record 7.2	Active Record 8.0
3.1	✓	✓	—
3.2	✓	✓	✓
3.3	✓	✓	✓
3.4	✓	✓	✓
4.0	✓	✓	✓

Ruby 3.1 with Active Record 8.0 is excluded because Active Record 8.0 requires Ruby 3.2 or newer. PostgreSQL and MySQL each have an Active Record 8.0 smoke job. Rails main runs as an allowed-failure forward-compatibility job.

The patches target private Active Record transaction APIs. Unsupported API shapes produce a warning and automatically disable detection unless strict_patching is enabled.

Performance

The non-nested path only checks whether a transaction is already open and then immediately delegates to Active Record.

benchmark/non_nested_transaction.rb measured the following on Ruby 4.0.0, Active Record 8.0.2, and SQLite3:

Case	Iterations/second	Time/iteration
Without Rollwire	31,069.5	32.19 μs
With Rollwire	30,310.6	32.99 μs

The approximately 2.4% difference fell within benchmark-ips measurement error in that run. Reproduce it with:

bundle exec appraisal rails_8_0 ruby benchmark/non_nested_transaction.rb

Development

bundle install
bundle exec rake
bundle exec appraisal rails_7_1 rspec
bundle exec appraisal rails_7_2 rspec
bundle exec appraisal rails_8_0 rspec
bundle exec rake build

License

Rollwire is available under the MIT License.