That "Download CSV" button works fine until your database hits a few million rows. Then exports time out, workers get OOM-killed, and files arrive truncated. This guide covers the streaming, async job, and query optimization patterns that fix large Rails CSV exports for good, plus what every Rails team needs to know about Active Storage security after CVE-2026-66066.

Every extra second between a click and a response costs you trust. Here’s how we think about Rails background jobs in practice: Active Job, Solid Queue vs Sidekiq, the transactional race condition that catches almost everyone once, and what actually belongs in a job versus what doesn’t.

A single unscoped query can hand one customer's data to another, and no amount of marketing undoes that. Four concrete data isolation problems we see in real multi-tenant Rails work, including one we've hit and fixed ourselves, and the patterns that prevent them.