Data & Connections

Turso, an extension of libSQL (a SQLite fork), modifies the consistency model due to its network-accessible and replicated nature, deviating from SQLite’s strictly serializable standard.

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Establishing Connections

Database operations begin with a client establishing either an HTTP or websocket connection to a server instance. Following this, an internal SQLite database connection is set up within the server to facilitate the operations.

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Data Consistency

Database operations are tightly controlled to maintain order and data integrity, with primary instances handling all writes in a serialized manner and replicas managing local reads.

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Primary Database Operations

• All operations are linearizable, maintaining an ordered history.
• Writes are fully serialized, with subsequent writes awaiting transaction completion.
• Users should exercise caution with long-running or abandoned transactions to prevent blocking other writes.

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Replica Operations & Reads

• Forwarding Writes to the Primary:
  • All writes are forwarded to the primary, ensuring serialized application.
• Replication Process:
  • Changes from the primary are eventually propagated to each replica, with a latency of 200-300ms.
  • New connections may encounter stale data until a write operation updates the replication index.
  • Replicas do not guarantee immediate reflection of primary’s changes, leading to potential data differences across replicas.
  • Monotonic reads are maintained, ensuring read operations retrieve data newer than previously accessed data on the same instance.
• Immediate Read-After-Write Consistency:
  • Replication index tracking enables immediate read-after-write consistency.
  • Clients track replication frames to ensure awareness of the most recent data state across replicas.
  • Replicas manage requests based on the client’s replication index, ensuring consistent data access.
  • Developers can utilize a driver to track replication frames, guaranteeing consistency between read and write operations.

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Transactional Consistency

• Transactions in libSQL, encompassing both batch and interactive transactions, adhere to SQLite’s transaction semantics.
• libSQL provides snapshot isolation for read operations, ensuring immediate visibility of writes within the same process. This guarantees serializability and isolation from other transactions.