Function accept_node_epoch 

async fn accept_node_epoch(
    kv_backend: &dyn KvBackend<Error = Error>,
    node_id: u64,
    node_epoch: u64,
) -> Result<bool>

Returns whether node_epoch is not lower than the highest epoch recorded for the datanode, raising the record when it is higher. An epoch too far ahead of this metasrv’s clock is refused, since recording it would fence every later process.