Ledger database
A database type optimized for an immutable, verifiable transaction history — like a digital ledger. Every change is a new entry, nothing is overwritten. Use case: financial accounting, audit trails, systems where "who changed what when" must be provable.
Examples: Amazon QLDB (being retired 2025), TigerBeetle (open source, optimized for financial transactions, millions/sec), immudb. Cryptographic verifiability: often a hash chain/Merkle tree so tampering is detectable. Distinct from a regular DB with an audit table: the immutability is built in and provable, not dependent on an admin not changing things. Double-entry bookkeeping is modeled naturally. TigerBeetle is especially hot for fintech 2024+ (debit/credit primitives, deterministic). Distinct from a blockchain: centralized, no consensus between untrusted parties.