If a hot key expires, you can stampede your DB. race_condition_ttl lets one process recompute while others serve stale content briefly. This is a reliability pattern masquerading as caching.

ETags are a simple high-impact performance lever: they reduce bandwidth and controller CPU. Use stale? with a stable ETag component list and last_modified so intermediary caches and browsers can do conditional GET.

Authorization filters often become string-SQL soup. Use Arel to build composable scopes that are still readable and safe. This snippet shows a “visible_to(member)” scope with a join and a condition that can evolve without turning into interpolated SQL

Enqueueing jobs inside a transaction can create “ghost jobs” when the transaction rolls back. Use after_commit or after_create_commit to enqueue work only after the DB commit succeeds.

Counter caches drift (deleted records, backfills, manual SQL). A repair job that recomputes counts safely is invaluable. It’s the kind of operational code you’re glad you wrote the first time a dashboard is wrong.

OFFSET gets slower as tables grow and becomes inconsistent under writes. Keyset pagination is stable and fast: paginate by (created_at, id) cursor. This is a common “senior Rails” upgrade for activity feeds.

For apps with replicas, route read-only code paths to reading role and enforce prevent_writes. This is a strong reliability move: accidental writes on replicas become exceptions instead of silent data loss.

I instrument services because I don’t want performance and reliability to be a guessing game. In Service instrumentation, I wrap the work in ActiveSupport::Notifications.instrument and emit a stable payload (things like IDs and counts, not giant blobs

I use ActiveSupport::CurrentAttributes any time I need request-scoped context without turning my app into a tangle of thread-local globals. In Current, I define the attributes I care about (member, request_id, remote_ip) and I use the resets hook to c

I wrapped external HTTP calls once I realized most “flaky APIs” were actually my fault: no timeouts, unclear retries, and logs that didn’t tell a story. In Client with timeouts, I centralize a Faraday connection with explicit open_timeout and timeout,

I’ve had endpoints where the same lookups get repeated across helpers and partials, and I didn’t want to pay for query caching on every request. In Scoped query cache, I wrap only the expensive report build in ActiveRecord::Base.cache, so the cache li

I enable strict loading when I want N+1 bugs to fail loudly during development instead of quietly shipping to production. In Enable strict_loading on associations, I mark the relationships that routinely get iterated (has_many :line_items and belongs_