#system-design

2 articles

system-designbackend

The Payment That Charged Twice

A retry is not a duplicate request — until it is. How idempotency keys actually work, why the naive version still double-charges, and the exact Postgres constraint that makes the guarantee real.

September 9th, 20268 min read

backendredis

Cache Invalidation, In Practice

The joke says it's one of the two hard problems. The reality is that most teams never write an invalidation strategy at all — they write a TTL and hope. Here is what the alternatives actually cost.

September 5th, 20269 min read