The onstat -x utility is useful for determining whether a global transaction is executing in loosely-coupled or tightly-coupled mode. The second position of the flags column displays the flags for global transactions. The T flag indicates tightly-coupled mode and the L flag indicates loosely-coupled mode.
Loosely-coupled mode means that the different database servers coordinate transactions but do not share locks. Each branch in a global transaction has a separate transaction XID. The records from all branches display as separate transactions in the logical log.
Tightly-coupled mode means that the different database servers coordinate transactions and share resources such as locking and logging. In a global transaction, all branches that access the same database share the same transaction XID. Log records for branches with the same XID appear under the same session ID. MTS uses tightly-coupled mode.
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