Virtuoso supports all 4 isolation levels from dirty read to serializable, for both relational and RDF data.

The recommended default isolation is read-committed, which offers a clean historical read of data that has uncommitted updates. This mode is similar to the Oracle default isolation and guarantees that no uncommitted data is seen, and that no read will block waiting for a lock held by another client.

There is transaction logging and roll forward recovery, with two phase commit used in Virtuoso Cluster if an update transaction modifies more than one server.

For RDF workloads which typically are not transactional and have large bulk loads, we recommend running in a "row autocommit" mode without transaction logging. This virtually eliminates log contention but still guarantees consistent results of multithreaded bulk loads.

Setting this up requires some consultancy and custom development but is well worthwhile for large projects.