_metcd/etcd_store.go
func (s *etcdStore) Compact(ctx context.Context, req *etcdserverpb.CompactionRequest) (*etcdserverpb.CompactionResponse, error) {
	// We don't have snapshotting yet, so compact just puts us in a bad state.
	// TODO(pb): fix this when we implement snapshotting.
	return nil, errors.New("not implemented")
}
func (s *etcdStore) Compact(ctx context.Context, req *etcdserverpb.CompactionRequest) (*etcdserverpb.CompactionResponse, error) {
	// We don't have snapshotting yet, so compact just puts us in a bad state.
	// TODO(pb): fix this when we implement snapshotting.
	return nil, errors.New("not implemented")
}
// Compact implements gRPC KVServer.
// Compact compacts the event history in s. User should compact the
// event history periodically, or it will grow infinitely.