The request for Commit][google.spanner.v1.Spanner.Commit].
Required. The transaction in which to commit.
Execute mutations in a temporary transaction. Note that unlike
commit of a previously-started transaction, commit with a
temporary transaction is non-idempotent. That is, if the
CommitRequest is sent to Cloud Spanner more than once (for
instance, due to retries in the application, or in the
transport library), it is possible that the mutations are
executed more than once. If this is undesirable, use
BeginTransaction][google.spanner.v1.Spanner.BeginTransaction]
and Commit][google.spanner.v1.Spanner.Commit] instead.