04 / case study 02
Ledger Core
- Role
- Tech lead
- Team
- Four engineers
- Year
- 2025
Drop architecture diagram or product shot
- 42ms
- p99 write latency
- 9.4B
- events per month
- 0
- reconciliation breaks
the problem
Balances were computed from a mutable table. Every incident ended the same way — three people, one spreadsheet, and a guess about which number was true.
the approach
Append-only entries, deterministic replay, and a reconciler running continuously instead of at month end. The ledger became the source of truth, not a report of it.