Optimizing Shiny App Performance

Make an existing Shiny for R app faster without changing what it does. The typical user has an app that worked fine for one or two developers and is now too slow or must support more users. Keep all app logic intact; prefer code changes over deployment tuning; resist rewrites.

Order of preference for every fix:

1. Eliminate work that isn't needed (don't compute outputs nobody is looking at; don't compute with inputs that aren't ready).
2. Reuse work that repeats (shared reactives, caching).
3. Accelerate unavoidable work (faster data formats, vectorized code).
4. Relocate work that blocks (async / background tasks) — last resort; it buys concurrency, not raw speed.

Workflow

1. Understand the complaint