Not all distributed transactions require two-phase commit. For example, a transaction that does not update, or that updates only one database, requires no coordination between databases. In this case, Ingres Star uses a single-phase commit that consists of sending commit messages to each database.

Sometimes a distributed transaction cannot use the two-phase commit protocol because one of the databases involved does not support it. For example, the following do not support two-phase commit:

Such databases may still participate in a distributed transaction if their data is not updated, or if the databases are at the only site that is updated in a transaction. If only one site not capable of two-phase commit is involved in a multi-site update, Ingres Star will simulate two-phase commit using the protocol described in the Simulated Two-Phase Commit section.