This module lets you average tensors in a decentralized manner.

class hivemind.averaging.DecentralizedAverager(averaged_tensors: Sequence[torch.Tensor], dht: DHT, *, start: bool, prefix: str, target_group_size: int, min_group_size: int = 2, initial_group_bits: Optional[str] = None, averaging_expiration: float = 15, request_timeout: float = 3, averaging_alpha: float = 1.0, part_size_bytes: int = 1048576, allreduce_timeout: Optional[float] = None, compression_type: runtime_pb2.CompressionType = 0, bandwidth: Optional[float] = None, min_vector_size: int = 0, auxiliary: bool = False, allow_state_sharing: Optional[bool] = None, client_mode: bool = False, listen_on: Endpoint = '*', daemon: bool = True, announced_host: Optional[str] = None, channel_options: Sequence[Tuple[str, Any]] = (), shutdown_timeout: float = 5, **kwargs)[source]

Parameter averaging service. A trainer can run this service in background to periodically average his parameters with other trainers. The averaging pattern is chosen so that (1) you only need to average with a small group of peers at a time, but (2) all trainers will converge to global average in a logarithmic number of steps.

  • averaged_tensors – a sequence of pytorch tensors that will be averaged in each all-reduce
  • dht – a DHT node that will be used to find groups
  • start – if True, starts the background process immediately
  • prefix – a shared prefix for all group keys
  • target_group_size – attempts to form groups with up to this many peers (recommended: a power of 2, e.g. 16)
  • initial_group_bits – a string of bits (‘0’ and ‘1’) that define the initial group key (bucket index)
  • averaging_expiration – attempt to find a group for this many seconds, otherwise try again note - this expiration time only applies to looking for group, passing tensors in allreduce may take more time
  • compression_type – optionally compress tensors with this compression algorithm before sending them to peers
  • allreduce_timeout – spend at most this many seconds for allreduce (after group is formed)
  • averaging_alpha – optional “learning rate” for averaging. If specified, local parameters will be shifted towards the (estimated) average by this coefficient. By default, local parameters are set equal to average.
  • request_timeout – when looking for group, wait for a response from leader for at most this many seconds.
  • part_size_bytes – tensors for AllReduce are processed in parts of up to this size (after compression)
  • bandwidth – if specified, this value represents the network bandwidth available to averager. By default, the averager is assumed to have the average bandwidth of his group. If bandwidth == 0, averager will rely on its groupmates to do all the averaging.
  • client_mode – if False (default), this averager will accept incoming requests from other peers if True, the averager will only join existing groups where at least one peer has client_mode=False
  • listen_on – network interface, e.g. “” or “localhost:” ( means pick any port) or “[::]:7654”
  • announced_host – visible IP address the averager will announce for external connections from other peers. If None, the address will be chosen from p2p.get_visible_maddrs() (global IPv4 addresses are preferred)
  • channel_options – options for grpc.aio.insecure_channel, e.g. [(‘grpc.enable_retries’, 0)] see for a list of all options
  • kwargs – extra parameters forwarded to grpc.aio.server
  • auxiliary – if this flag is specified, averager.step will only assist others without sending local tensors for averaging
  • allow_state_sharing – if set to True, other peers can download this peer’s state. Can be overwritten with averager.allow_state_sharing = True / False
  • shutdown_timeout – when calling .shutdown, wait for up to this many seconds before terminating

request_timeout must be smaller than averaging_expiration to avoid potential deadlocks.


>>> averager = DecentralizedAverager(...)
>>> with averager.get_tensors() as tensors:
>>>     # run some code, modify tensors if necessary
>>>     tensors[0] += 1
>>> # do not use tensors after the lock is released
>>> metadata = averager.step(gather=dict(my_batch_size=32))
>>> # run averaging once (in-place), gather metadata from groupmates
>>> with averager.get_tensors() as tensors_after_averaging:
>>>     pass # use the averaged tensors

alias of hivemind.utils.serializer.MSGPackSerializer


if set to True, other peers can download this peer’s state


Run averager function in a background thread; this is needed to avoid a heisenbug with broken OMP on fork Turns out, using a non-main thread creates a separate OMP pool that works even if the original pool is corrupted Read more:

run_in_background(await_ready=True, timeout=None)[source]

Starts averager in a background process. if await_ready, this method will wait until background dht is ready to process incoming requests or for :timeout: seconds max.

shutdown() → None[source]

Shut down the averager process

step(gather: Optional[Any] = None, weight: Optional[float] = None, timeout: Optional[float] = None, allow_retries: bool = True, wait: bool = True) → Union[Dict[str, Any], None, hivemind.utils.mpfuture.MPFuture][source]

Set up the averager to look for a group and run one round of averaging, return True on success, False on failure

  • gather – optionally send this informaton to all peers in the next group and gather it from every groupmate (this operation is known as all-gather). The gathered data will be available as the output of this function.
  • weight – averaging weight for this peer, int or float, must be strictly positive
  • allow_retries – if averager fails to run one round of allreduce, this option will allow it to try again within the specified timeout
  • timeout – if averager was unable to find a group in this many seconds, consider allreduce failedK
  • wait – if True (default), return when finished. Otherwise return MPFuture and run in background.

on success, update averaged_tensors and return group info; on failure, return None

get_current_state() → Tuple[Any, Sequence[torch.Tensor]][source]

Get current state and send it to a peer. executed in the host process. Meant to be overriden. :returns: a tuple of (small metadata, sequence of torch tensors) :note: metadata must be seriablizable with self.serializer (default = MSGPackSerializer)

load_state_from_peers(wait=True) → Optional[Tuple[Any, Sequence[torch.Tensor]]][source]

Try to download the latest optimizer state one of the existing peer. :returns: on success, return a 2-tuple with (metadata, tensors), where

  • metadata is a small object containing metadata (e.g. hyperparameters, scalars, etc)
  • tensors is a sequence of pytorch tensors meant to contain peer’s model weights and optimizer statistics

The exact contents of both metadata and tensors are determined by get_current_state method

rpc_download_state(request: averaging_pb2.DownloadRequest, context: grpc.ServicerContext) → AsyncIterator[averaging_pb2.DownloadData][source]

Get the up-to-date trainer state from a peer. The state consists of two parts: (serialized_metadata, tensors)

  • serialized_metadata is a small serialized bytestring meant to store scalars and hyperparameters
  • tensors is a sequence of pytorch tensors that represent model parameters or optimizer statistics
get_group_bits(wait: bool = True)[source]
Parameters:wait – if True, return bits immediately. Otherwise return awaitable MPFuture
Returns:averager’s current group key bits (without prefix)
set_group_bits(group_bits: str, wait: bool = True)[source]
  • group_bits – group bits (string of ‘0’ or ‘1’) to be used in averager’s group key
  • wait – if True, wait until the update is confirmed by the averager. Otherwise return immediately