>> Can you please elaborate what is not supported
The idea is to prevent dirty reads. As I understand it, it's possible in a distributed transaction to get a non-repeatable read bnecause the read consistency does not work across databases.
In the serializable
transaction isolation level non-repeatable
reads are not possible.
From the docs, read about "in question" transactions:http://docs.oracle.com/cd/B10501_01/server...521/ds_txns.htm