Facet: point-in-time restore for thousands of SQLite databases at $0.0034 per tenant

Facet described a point-in-time restore system for per-creator SQLite databases, using chains of signed snapshots and WAL segments in Cloudflare R2. At 100,000 tenants, R2 costs are projected at about $342 a month, or roughly $0.0034 per tenant. The team also fixed a bug where restore could pick a stale chain.

• One 32 GB box holds 500 tenants warm at about 6.6 MB RAM each
• The shipper runs inside the same Go process and does its own checkpoints
• About 17 write operations per tenant per day, ~$342/month at 100,000 tenants
• Bug: restore picked the chain by epoch number instead of time