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Unlike most SQL databases, which default to weaker isolation levels for performance reasons, Volt DB chooses to provide strict serializable isolation by default: the combination of serializability’s multi-object atomicity, and linearizability’s real-time constraints.
Serializability is the strongest of the four ANSI SQL isolation levels: transactions must appear to execute in some order, one at a time.
Volt DB targets these applications—and offers them the strongest claims of any database we’ve tested with Jepsen: strict serializable isolation.
In this work, we aim to verify those safety claims.
Volt DB’s engineers confirm this interpretation: it should provide strict serializability.
Because strict serializable systems are also linearizable, we can use Jepsen’s existing linearizability checker to verify Volt DB’s correctness—both on single objects in the database, and on systems of multiple rows.
Volt DB’s documentation explicitly claims serializability, but implicitly claims strict serializability as well.
For instance, their transaction whitepaper asserts: Because Volt DB always performs synchronous replication of read-write transactions within a partition, end-users are guaranteed to read the results of prior writes even when reads bypass the SPI sequencer The guarantee that prior writes are visible to clients suggests that Volt DB’s transactions obey linearizability’s real-time constraint.
Serializability requires transactions appear to execute in may always return 0, regardless of the number of users currently in the table, because when the table was first created, it had no contents.Volt DB can shard tables into logical for redundancy.Transactions which only interact with data in a single partition can be executed by that partition’s SPI, without coordinating with other partitions.In contrast to updates, pure-read transactions are ordered by the SPI, and read local state directly off any replica.Operations across multiple partitions are ordered by a single Multi-Partition Initiator (MPI) for the entire cluster, which issues operations to relevant SPIs for execution on their partitions.