# JSR

> @mikehall314/cushion on JSR: A CouchDB-style document database for Deno.

- **Website:** https://jsr.io/@mikehall314/cushion
- **Pricing:** unknown
- **Categories:** Writing & Content, Design
- **Tags:** writing-content, design
- **Platforms:** Web
- **Last verified:** 2026-09-10
- **Canonical page:** https://linkrena.com/tools/jsr

## About

A CouchDB-style document database for Deno. Cushion gives you documents with optimistic concurrency, map-reduce views, and a query builder - powered by PouchDB and backed by Deno KV.

Cushion implements the PouchDB adapter interface directly against Deno KV. It gets you a real PouchDB: rev trees, conflict resolution, map/reduce views, and replication, backed by Deno's built-in database.

Revisions are tracked automatically, giving you optimistic concurrency for free: if two writers update the same document concurrently, the loser gets a 409 and should re-read and retry.

Two helpers to make the map-reduce API a little more ergonomic to work with.

Deno KV imposes a 64 KiB limit per value, so a single document revision (or attachment) larger than that will fail to write. Deno KV atomic operations are also capped at 1000 mutations and roughly 800 KiB total; cushion chunks large bulkDocs batches across multiple atomic commits, which means a very large batch is not atomic as a whole. Batches under ~100 document writes commit in one atomic operation.

Writes within a process are serialised, and cross-process writers are handled with an optimistic versionstamp check and retry (3 attempts). Under sustained contention from many processes a write can fail with a 409 after retries are exhausted.

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