func (txn *Txn) Discard() {
	if txn.discarded { // Avoid a re-run.
		return
	}
	if atomic.LoadInt32(&txn.numIterators) > 0 {
		panic("Unclosed iterator at time of Txn.Discard.")
	}
	txn.discarded = true
	if !txn.db.orc.isManaged {
		txn.db.orc.readMark.Done(txn.readTs)
	}
	if txn.update {
		txn.db.orc.decrRef()
	}
}
func (txn *Txn) Discard() {
	if txn.discarded { // Avoid a re-run.
		return
	}
	if atomic.LoadInt32(&txn.numIterators) > 0 {
		panic("Unclosed iterator at time of Txn.Discard.")
	}
	txn.discarded = true
	if !txn.db.orc.isManaged {
		txn.db.orc.readMark.Done(txn.readTs)
	}
	if txn.update {
		txn.db.orc.decrRef()
	}
}
// Discard discards a created transaction. This method is very important and must be called. Commit
// method calls this internally, however, calling this multiple times doesn't cause any issues. So,
// this can safely be called via a defer right when transaction is created.
//
// NOTE: If any operations are run on a discarded transaction, ErrDiscardedTxn is returned.