The txnabort command causes an abnormal termination of the
transaction.
The log is played backwards and any necessary recovery operations are
performed. After recovery is completed, all locks held by the
transaction are acquired by the parent transaction in the case of a
nested transaction or released in the case of a non-nested transaction.
As is the case for txncommit, applications that require strict
two-phase locking should not explicitly release any locks.
In the case of nested transactions, aborting the parent transaction
causes all children of that transaction to be aborted.
Once txnabort has been called, regardless of its return, the
txn handle may not be accessed again.
The txnabort command returns 0 on success, and in the case of error, a Tcl error
is thrown.