AI-generated editorial illustration; not a documentary photograph.
Perplexity has moved part of its production search traffic from DynamoDB to CobbleDB, a custom Rust key-value store built by two engineers in two months with help from hundreds of coding agents. The New Stack reports that the agents contributed to development but did not control the production database. Perplexity says the move has reduced read latency and expects lower costs, though neither comparison settles the full cost of maintaining the system.
Why Search Needed a Change
A search request can require the serving layer to retrieve batches of stored passages and vector embeddings. Perplexity wanted more control over how those reads were handled: under its DynamoDB setup, a slow replica could delay a batch. The steady volume of large reads and writes also made the managed service increasingly expensive for its workload.
How CobbleDB Fits
Perplexity separated durable document storage from the database serving live searches. Updates pass through a batching layer before reaching CobbleDB, where processed page data is distributed across three replicas per partition. A router can try another replica when one responds slowly, while replicas apply updates independently. That design gives the company control over a read path it could not tune in the same way with DynamoDB.
Results and Caveats
Perplexity measured median batch-read latency of 5.6 milliseconds on CobbleDB, versus 31.4 ms recorded on DynamoDB before the cutover. Its p99 figure fell from 123 ms to 24.2 ms. These were not side-by-side tests against identical traffic, so the figures should not be treated as a controlled comparison.
The company's cost model projects savings of at least 20% against the DynamoDB commitment options it evaluated. That estimate excludes the engineering work required to support a custom database.
Agents Without Production Control
The coding agents helped with fixes and tests, including issues involving restore assumptions and runtime configuration. The two engineers retained responsibility for the architecture and production system. CobbleDB is running for part of Perplexity's traffic, but it is not yet open-source; the company plans to release it later.
Source: Perplexity’s AI agents helped build a database. They weren’t allowed to run it.
SIGNAL TITANS
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