You can see the usage of distributed transaction slots in V$RESOURCE_USAGE under 8i. You can also see the distributed transaction branches in V$TRANSACTION but they are not easy to distinguish from other transactions. You could join the address to X$K2GTE (the global transaction mapping table) but perhaps an easier solution is just to look for sessions holding DX enqueue locks.

Remember that distributed queries use distributed transaction slots and so need to be followed by a commit (much as I hate telling people to commit lest they go overboard and cause LGWR performance problems).

I am getting the error message: too many distributed transactions.

How do I determine the number of active distributed transactions and the sessions that are keeping them?