type Backend interface {
	ReadTx() backend.ReadTx
}

type ConsistentIndexer interface {
	// ConsistentIndex returns the consistent index of current executing entry.
	ConsistentIndex() uint64

	// ConsistentApplyingIndex returns the consistent applying index of current executing entry.
	ConsistentApplyingIndex() (uint64, uint64)

	// UnsafeConsistentIndex is similar to ConsistentIndex, but it doesn't lock the transaction.
	UnsafeConsistentIndex() uint64

	// SetConsistentIndex set the consistent index of current executing entry.
	SetConsistentIndex(v uint64, term uint64)

	// SetConsistentApplyingIndex set the consistent applying index of current executing entry.
	SetConsistentApplyingIndex(v uint64, term uint64)

	// UnsafeSave must be called holding the lock on the tx.
	// It saves consistentIndex to the underlying stable storage.
	UnsafeSave(tx backend.UnsafeReadWriter)

	// SetBackend set the available backend.BatchTx for ConsistentIndexer.
	SetBackend(be Backend)
}