performance

The N+1 query problem is Django's most common performance trap. I use select_related for foreign key and one-to-one relationships (performs SQL JOIN), and prefetch_related for many-to-many and reverse foreign keys (separate queries with Python join).

Computing counts on associations can be expensive when done repeatedly—post.comments.count executes a SELECT COUNT(*) query every time. Counter caches solve this by maintaining a denormalized count column on the parent model that increments/decrements

Rails caching dramatically improves performance by avoiding expensive computations and queries. Fragment caching caches view partials. Russian doll caching nests cache fragments for efficient invalidation. Low-level caching stores arbitrary data. Rail

Some read paths want a denormalized shape without materializing a new table. Postgres views are a clean option. Keep the view definition in a migration and map it with a read-only model.

Indexes dramatically speed up queries but slow down writes. B-tree indexes handle equality and range queries—default for most databases. I create indexes on foreign keys, frequently queried columns, and WHERE/ORDER BY clauses. Composite indexes order

Not all queries benefit from a full-table index, especially when most rows are ‘inactive’ or archived. A partial index lets you index only the subset you care about (like active users or un-deleted records), which shrinks index size and improves cache

For slow endpoints, I like a skeleton placeholder rather than a blank area. Turbo Frames make this easy: render a “loading skeleton” inside the frame tag as the initial content, then set src so Turbo fetches the real content. When the response arrives

Infinite scroll improves perceived performance by loading content as users reach the bottom of the page. I combine Turbo Frames with the Intersection Observer API via a Stimulus controller. The last item in each page has a sentinel element that, when

Prefetching data when users hover over links makes navigation feel instant. React Query's prefetchQuery loads data into cache before users click. When they navigate, the data is already available and renders immediately. I use the onMouseEnter event o

Skeleton screens show content placeholders while data loads, making apps feel faster than spinners. I create skeleton components that match the layout of actual content with subtle pulsing animations. React Query's isLoading flag determines whether to

Long-running requests tie up worker threads and degrade overall application responsiveness. Rack::Timeout enforces request timeouts at the Rack layer, killing requests that exceed configured limits. I set conservative timeouts (15-30 seconds) and hand

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.