Perplexity’s AI agents helped build a database. They weren’t allowed to run it.

Perplexity decided it was paying too much for DynamoDB and wasn’t getting the control it wanted over read performance. So it built its own database: CobbleDB.

Built by two engineers in two months with help from hundreds of persistent coding agents throughout development, CobbleDB is a roughly 40,000-line Rust key-value store that now handles part of Perplexity’s production search traffic. The company measured median batch-read latency at 5.6 milliseconds after the move, compared with 31.4 ms on DynamoDB before the cutover, while p99 went from 123 ms to 24.2 ms.

It’s expected to cost at least 20% less than DynamoDB and plans to open-source the database at some point.

But the database itself is only part of the story. CMU professor Andy Pavlo argued at Percona Live earlier this year that databases are the hardest and most important challenge for AI agents, in part because mistakes involving production data can be difficult or impossible to reverse.

Perplexity went ahead and used hundreds of agents to help build one anyway, but they weren’t given the keys to production.

It’s expected to cost at least 20% less than DynamoDB and plans to open-source the database at some point.

Why DynamoDB couldn’t keep up

Each search requires the serving layer to retrieve pre-chunked passages and vector embeddings, with a single Search API call fetching 100 to 120 page keys in batches of 10 to 20. Each item averages about 50 KB.

DynamoDB gave…