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Catena is a distributed database based on a blockchain, accessible using SQL. Catena timestamps database transactions (SQL) in a decentralized way between nodes that do not or cannot trust each other. A Catena blockchain contains SQL transactions that, when executed in order, lead to the agreed-upon state of the database. The transactions are automatically replicated to, validated by, and replayed on participating clients. A Catena database can be connected to by client applications using the PostgreSQL wire protocol (pq).