fPreviousID
fPreviousID = block->previous_transaction->id;
fHasParent ? 'p' : '-', fTransactionID, fPreviousID);
int32 fPreviousID;
fCPU, fPreviousID);
thread_id PreviousThreadID() const { return fPreviousID; }
thread_id fPreviousID;
fPreviousID(previous->id),