Wallet Ledger Systems — how they work and why they matter

Overview

Wallet systems hinge on an auditable, double‑entry ledger. Every change in balance must have a counterpart entry to keep the system consistent.

Key Concepts

• Double‑entry: debit one account, credit another, sums to zero
• Atomic transfers: either the whole transfer happens or none of it
• Invariants: balances derived from the ledger, never stored separately
• Idempotent operations: safe retries using transfer keys

Architecture Notes

1. Command API for writes; Query API for reads (CQRS)
2. Ledger store with normalized entries and indexes
3. Transfer service enforces invariants and idempotency
4. Read replicas for statements and balances

Why it matters

• Prevents drift in balances
• Enables reconciliation and audit at any time
• Scales with read replicas while protecting write consistency