The Write Last, Read First Rule
12 days ago
- #database
- #consistency
- #transactions
- TigerBeetle is a financial transactions database designed for correctness, focusing on double-entry bookkeeping with accounts and transfers.
- The system separates master data (stored in Postgres) from transaction data (stored in TigerBeetle) to scale independently and meet different security and compliance needs.
- Transactions in TigerBeetle are atomic, but composing transactions across systems (Postgres and TigerBeetle) requires coordination to maintain consistency.
- The system must uphold safety properties like consistency (every account in Postgres has a corresponding account in TigerBeetle and vice versa) and traceability (every account in TigerBeetle with a positive balance corresponds to an account in Postgres).
- TigerBeetle is designated as the system of record, meaning it determines the existence of an account, while Postgres is the system of reference.
- The 'Write Last, Read First' principle ensures consistency: write to the system of reference first, then the system of record; read from the system of record first.
- Operations must be idempotent to handle disruptions and ensure eventual completion, leveraging frameworks like Resonate's Distributed Async Await.
- The application layer interprets subsystem responses (Postgres and TigerBeetle) to enforce application-level semantics and detect violations like ordering conflicts or data inconsistencies.
- Correctness is achieved through careful design, durable executions, intentional ordering, and idempotent operations, even in the absence of transactions.