The design library
Building blocks, complete architectures, and variations worth comparing. Search by the problem you want to solve or a component you want to understand.
Building blockOfficial
Positions written to a cell-based index with a short expiry, so "who is near me" is a small read and anything that stops reporting disappears on its own.
Building blockOfficial
A bucket of tokens per key, refilled at a fixed rate, with refill-and-take done atomically in one place so every server agrees.
Building blockOfficial
Push new items into followers' timelines at write time, except for accounts with huge followings, whose posts are pulled and merged at read time.
Building blockOfficial
The service reads the cache first and fills it on a miss, so the cache holds only what is actually asked for and an outage degrades to slow rather than down.