Physix FrontierPhysix Frontier · News Briefing Card (Hacker News · Oct 13, 2026)
Perplexity ships in-house CobbleDB, AI agents helped build it
KEY FACTS
- Perplexity built CobbleDB, its own key-value store, to replace DynamoDB, completing the work with two engineers over two months.
- CobbleDB spans roughly 40,000 lines of Rust code and already carries part of Perplexity's production search traffic.
- Hundreds of coding agents took part in development, but none were allowed to run the production database.
- After the switch, median batch read latency fell from 31.4 milliseconds to 5.6 milliseconds, and p99 dropped from 123 milliseconds to 24.2 milliseconds.
- Perplexity expects CobbleDB to cost at least 20% less than DynamoDB and plans to open-source it in the future.
KEY DATA
about 40,000 linesLines of code
5.6 millisecondsMedian batch read latency
24.2 millisecondsp99 latency
at least 20%Expected cost reduction
PHYSIX OBSERVATION
AI agents can write code but cannot touch the production database, and that boundary deserves more attention than the latency numbers. Perplexity replaced a managed service with two people in two months, showing that AI assistance is making it feasible for small teams to build their own infrastructure; but the savings on the bill do not account for long-term maintenance costs, and the ledger on a self-built database has to be reckoned in years.
Source: Hacker News report