DataLoader

class dgl.dataloading.DataLoader(graph, indices, graph_sampler, device=None, use_ddp=False, ddp_seed=0, batch_size=1, drop_last=False, shuffle=False, use_prefetch_thread=None, use_alternate_streams=None, pin_prefetcher=None, use_uva=False, **kwargs)[source]

Bases: torch.utils.data.dataloader.DataLoader

Sampled graph data loader. Wrap a DGLGraph and a Sampler into an iterable over mini-batches of samples.

DGL’s DataLoader extends PyTorch’s DataLoader by handling creation and transmission of graph samples. It supports iterating over a set of nodes, edges or any kinds of indices to get samples in the form of DGLGraph, message flow graphs (MFGS), or any other structures necessary to train a graph neural network.

Parameters

  • graph (DGLGraph) – The graph.

  • indices (Tensor or dict[ntype, Tensor]) –

    The set of indices. It can either be a tensor of integer indices or a dictionary of types and indices.

    The actual meaning of the indices is defined by the sample() method of graph_sampler.

  • graph_sampler (dgl.dataloading.Sampler) – The subgraph sampler.

  • device (device context, optional) –

    The device of the generated MFGs in each iteration, which should be a PyTorch device object (e.g., torch.device).

    By default this value is None. If use_uva is True, MFGs and graphs will generated in torch.cuda.current_device(), otherwise generated in the same device of g.

  • use_ddp (boolean, optional) –

    If True, tells the DataLoader to split the training set for each participating process appropriately using torch.utils.data.distributed.DistributedSampler.

    Overrides the sampler argument of torch.utils.data.DataLoader.

  • ddp_seed (int, optional) –

    The seed for shuffling the dataset in torch.utils.data.distributed.DistributedSampler.

    Only effective when use_ddp is True.

  • use_uva (bool, optional) –

    Whether to use Unified Virtual Addressing (UVA) to directly sample the graph and slice the features from CPU into GPU. Setting it to True will pin the graph and feature tensors into pinned memory.

    If True, requires that indices must have the same device as the device argument.

    Default: False.

  • use_prefetch_thread (bool, optional) –

    (Advanced option) Spawns a new Python thread to perform feature slicing asynchronously. Can make things faster at the cost of GPU memory.

    Default: True if the graph is on CPU and device is CUDA. False otherwise.

  • use_alternate_streams (bool, optional) –

    (Advanced option) Whether to slice and transfers the features to GPU on a non-default stream.

    Default: True if the graph is on CPU, device is CUDA, and use_uva is False. False otherwise.

  • pin_prefetcher (bool, optional) –

    (Advanced option) Whether to pin the feature tensors into pinned memory.

    Default: True if the graph is on CPU and device is CUDA. False otherwise.

  • kwargs (dict) –

    Key-word arguments to be passed to the parent PyTorch torch.utils.data.DataLoader class. Common arguments are:

    • batch_size (int): The number of indices in each batch.

    • drop_last (bool): Whether to drop the last incomplete batch.

    • shuffle (bool): Whether to randomly shuffle the indices at each epoch.

Examples

To train a 3-layer GNN for node classification on a set of nodes train_nid on a homogeneous graph where each node takes messages from 15 neighbors on the first layer, 10 neighbors on the second, and 5 neighbors on the third (assume the backend is PyTorch):

>>> sampler = dgl.dataloading.MultiLayerNeighborSampler([15, 10, 5])
>>> dataloader = dgl.dataloading.DataLoader(
...     g, train_nid, sampler,
...     batch_size=1024, shuffle=True, drop_last=False, num_workers=4)
>>> for input_nodes, output_nodes, blocks in dataloader:
...     train_on(input_nodes, output_nodes, blocks)

Using with Distributed Data Parallel

If you are using PyTorch’s distributed training (e.g. when using torch.nn.parallel.DistributedDataParallel), you can train the model by turning on the use_ddp option:

>>> sampler = dgl.dataloading.MultiLayerNeighborSampler([15, 10, 5])
>>> dataloader = dgl.dataloading.DataLoader(
...     g, train_nid, sampler, use_ddp=True,
...     batch_size=1024, shuffle=True, drop_last=False, num_workers=4)
>>> for epoch in range(start_epoch, n_epochs):
...     for input_nodes, output_nodes, blocks in dataloader:
...         train_on(input_nodes, output_nodes, blocks)

Notes

Please refer to Minibatch Training Tutorials and User Guide Section 6 for usage.

Tips for selecting the proper device

  • If the input graph g is on GPU, the output device device must be the same GPU and num_workers must be zero. In this case, the sampling and subgraph construction will take place on the GPU. This is the recommended setting when using a single-GPU and the whole graph fits in GPU memory.

  • If the input graph g is on CPU while the output device device is GPU, then depending on the value of use_uva:

    • If use_uva is set to True, the sampling and subgraph construction will happen on GPU even if the GPU itself cannot hold the entire graph. This is the recommended setting unless there are operations not supporting UVA. num_workers must be 0 in this case.

    • Otherwise, both the sampling and subgraph construction will take place on the CPU.