hetero_rgcn.py

"""
This script is a GraphBolt counterpart of
``/examples/core/rgcn/hetero_rgcn.py``. It demonstrates how to use GraphBolt
to train a R-GCN model for node classification on the Open Graph Benchmark
(OGB) dataset "ogbn-mag" and "ogb-lsc-mag240m". For more details on "ogbn-mag",
please refer to the OGB website: (https://ogb.stanford.edu/docs/linkprop/). For
more details on "ogb-lsc-mag240m", please refer to the OGB website:
(https://ogb.stanford.edu/docs/lsc/mag240m/).

Paper [Modeling Relational Data with Graph Convolutional Networks]
(https://arxiv.org/abs/1703.06103).

This example highlights the user experience of GraphBolt while the model and
training/evaluation procedures are almost identical to the original DGL
implementation. Please refer to original DGL implementation for more details.

This flowchart describes the main functional sequence of the provided example.
main
│
├───> load_dataset
│     │
│     └───> Load dataset
│
├───> rel_graph_embed [HIGHLIGHT]
│     │
│     └───> Generate graph embeddings
│
├───> Instantiate RGCN model
│     │
│     ├───> RelGraphConvLayer (input to hidden)
│     │
│     └───> RelGraphConvLayer (hidden to output)
│
└───> run
      │
      │
      └───> Training loop
            │
            ├───> EntityClassify.forward (RGCN model forward pass)
            │
            └───> validate and test
                  │
                  └───> EntityClassify.evaluate
"""

import argparse
import itertools
import sys
import time

import dgl
import dgl.graphbolt as gb
import dgl.nn as dglnn

import psutil

import torch
import torch.nn as nn
import torch.nn.functional as F
from dgl.nn import HeteroEmbedding
from ogb.lsc import MAG240MEvaluator
from ogb.nodeproppred import Evaluator
from tqdm import tqdm


def load_dataset(dataset_name):
    """Load the dataset and return the graph, features, train/valid/test sets
    and the number of classes.

    Here, we use `BuiltInDataset` to load the dataset which returns graph,
    features, train/valid/test sets and the number of classes.
    """
    dataset = gb.BuiltinDataset(dataset_name).load()
    print(f"Loaded dataset: {dataset.tasks[0].metadata['name']}")

    graph = dataset.graph
    features = dataset.feature
    train_set = dataset.tasks[0].train_set
    valid_set = dataset.tasks[0].validation_set
    test_set = dataset.tasks[0].test_set
    num_classes = dataset.tasks[0].metadata["num_classes"]

    return (
        graph,
        features,
        train_set,
        valid_set,
        test_set,
        num_classes,
    )


def create_dataloader(
    name,
    graph,
    features,
    item_set,
    device,
    batch_size,
    fanouts,
    shuffle,
    num_workers,
):
    """Create a GraphBolt dataloader for training, validation or testing."""

    ###########################################################################
    # Initialize the ItemSampler to sample mini-batches from the dataset.
    # `item_set`:
    #   The set of items to sample from. This is typically the
    #   training, validation or test set.
    # `batch_size`:
    #   The number of nodes to sample in each mini-batch.
    # `shuffle`:
    #   Whether to shuffle the items in the dataset before sampling.
    datapipe = gb.ItemSampler(item_set, batch_size=batch_size, shuffle=shuffle)

    # Move the mini-batch to the appropriate device.
    # `device`:
    #   The device to move the mini-batch to.
    datapipe = datapipe.copy_to(device, extra_attrs=["seeds"])

    # Sample neighbors for each seed node in the mini-batch.
    # `graph`:
    #   The graph(FusedCSCSamplingGraph) from which to sample neighbors.
    # `fanouts`:
    #   The number of neighbors to sample for each node in each layer.
    datapipe = datapipe.sample_neighbor(graph, fanouts=fanouts)

    # Fetch the features for each node in the mini-batch.
    # `features`:
    #   The feature store from which to fetch the features.
    # `node_feature_keys`:
    #   The node features to fetch. This is a dictionary where the keys are
    #   node types and the values are lists of feature names.
    node_feature_keys = {"paper": ["feat"]}
    if name == "ogb-lsc-mag240m":
        node_feature_keys["author"] = ["feat"]
        node_feature_keys["institution"] = ["feat"]
    datapipe = datapipe.fetch_feature(features, node_feature_keys)

    # Create a DataLoader from the datapipe.
    # `num_workers`:
    #   The number of worker processes to use for data loading.
    return gb.DataLoader(datapipe, num_workers=num_workers)


def extract_embed(node_embed, input_nodes):
    emb = node_embed(
        {ntype: input_nodes[ntype] for ntype in input_nodes if ntype != "paper"}
    )
    return emb


def extract_node_features(name, block, data, node_embed, device):
    """Extract the node features from embedding layer or raw features."""
    if name == "ogbn-mag":
        input_nodes = {
            k: v.to(device) for k, v in block.srcdata[dgl.NID].items()
        }
        # Extract node embeddings for the input nodes.
        node_features = extract_embed(node_embed, input_nodes)
        # Add the batch's raw "paper" features. Corresponds to the content
        # in the function `rel_graph_embed` comment.
        node_features.update(
            {"paper": data.node_features[("paper", "feat")].to(device)}
        )
    else:
        node_features = {
            ntype: data.node_features[(ntype, "feat")]
            for ntype in block.srctypes
        }
        # Original feature data are stored in float16 while model weights are
        # float32, so we need to convert the features to float32.
        node_features = {
            k: v.to(device).float() for k, v in node_features.items()
        }
    return node_features


def rel_graph_embed(graph, embed_size):
    """Initialize a heterogenous embedding layer for all node types in the
    graph, except for the "paper" node type.

    The function constructs a dictionary 'node_num', where the keys are node
    types (ntype) and the values are the number of nodes for each type. This
    dictionary is used to create a HeteroEmbedding instance.

    (HIGHLIGHT)
    A HeteroEmbedding instance holds separate embedding layers for each node
    type, each with its own feature space of dimensionality
    (node_num[ntype], embed_size), where 'node_num[ntype]' is the number of
    nodes of type 'ntype' and 'embed_size' is the embedding dimension.

    The "paper" node type is specifically excluded, possibly because these nodes
    might already have predefined feature representations, and therefore, do not
    require an additional embedding layer.

    Parameters
    ----------
    graph : FusedCSCSamplingGraph
        The graph for which to create the heterogenous embedding layer.
    embed_size : int
        The size of the embedding vectors.

    Returns
    --------
    HeteroEmbedding
        A heterogenous embedding layer for all node types in the graph, except
        for the "paper" node type.
    """
    node_num = {}
    node_type_to_id = graph.node_type_to_id
    node_type_offset = graph.node_type_offset
    for ntype, ntype_id in node_type_to_id.items():
        # Skip the "paper" node type.
        if ntype == "paper":
            continue
        node_num[ntype] = (
            node_type_offset[ntype_id + 1] - node_type_offset[ntype_id]
        )
    print(f"node_num for rel_graph_embed: {node_num}")
    return HeteroEmbedding(node_num, embed_size)


class RelGraphConvLayer(nn.Module):
    def __init__(
        self,
        in_size,
        out_size,
        ntypes,
        relation_names,
        activation=None,
        dropout=0.0,
    ):
        super(RelGraphConvLayer, self).__init__()
        self.in_size = in_size
        self.out_size = out_size
        self.ntypes = ntypes
        self.relation_names = relation_names
        self.activation = activation

        ########################################################################
        # (HIGHLIGHT) HeteroGraphConv is a graph convolution operator over
        # heterogeneous graphs. A dictionary is passed where the key is the
        # relation name and the value is the instance of GraphConv. norm="right"
        # is to divide the aggregated messages by each node’s in-degrees, which
        # is equivalent to averaging the received messages. weight=False and
        # bias=False as we will use our own weight matrices defined later.
        ########################################################################
        self.conv = dglnn.HeteroGraphConv(
            {
                rel: dglnn.GraphConv(
                    in_size, out_size, norm="right", weight=False, bias=False
                )
                for rel in relation_names
            }
        )

        # Create a separate Linear layer for each relationship. Each
        # relationship has its own weights which will be applied to the node
        # features before performing convolution.
        self.weight = nn.ModuleDict(
            {
                rel_name: nn.Linear(in_size, out_size, bias=False)
                for rel_name in self.relation_names
            }
        )

        # Create a separate Linear layer for each node type.
        # loop_weights are used to update the output embedding of each target node
        # based on its own features, thereby allowing the model to refine the node
        # representations. Note that this does not imply the existence of self-loop
        # edges in the graph. It is similar to residual connection.
        self.loop_weights = nn.ModuleDict(
            {
                ntype: nn.Linear(in_size, out_size, bias=True)
                for ntype in self.ntypes
            }
        )

        self.loop_weights = nn.ModuleDict(
            {
                ntype: nn.Linear(in_size, out_size, bias=True)
                for ntype in self.ntypes
            }
        )

        self.dropout = nn.Dropout(dropout)
        # Initialize parameters of the model.
        self.reset_parameters()

    def reset_parameters(self):
        for layer in self.weight.values():
            layer.reset_parameters()

        for layer in self.loop_weights.values():
            layer.reset_parameters()

    def forward(self, g, inputs):
        """
        Parameters
        ----------
        g : DGLGraph
            Input graph.
        inputs : dict[str, torch.Tensor]
            Node feature for each node type.

        Returns
        -------
        dict[str, torch.Tensor]
            New node features for each node type.
        """
        # Create a deep copy of the graph g with features saved in local
        # frames to prevent side effects from modifying the graph.
        g = g.local_var()

        # Create a dictionary of weights for each relationship. The weights
        # are retrieved from the Linear layers defined earlier.
        weight_dict = {
            rel_name: {"weight": self.weight[rel_name].weight.T}
            for rel_name in self.relation_names
        }

        # Create a dictionary of node features for the destination nodes in
        # the graph. We slice the node features according to the number of
        # destination nodes of each type. This is necessary because when
        # incorporating the effect of self-loop edges, we perform computations
        # only on the destination nodes' features. By doing so, we ensure the
        # feature dimensions match and prevent any misuse of incorrect node
        # features.
        inputs_dst = {
            k: v[: g.number_of_dst_nodes(k)] for k, v in inputs.items()
        }
        # Apply the convolution operation on the graph. mod_kwargs are
        # additional arguments for each relation function defined in the
        # HeteroGraphConv. In this case, it's the weights for each relation.
        hs = self.conv(g, inputs, mod_kwargs=weight_dict)

        def _apply(ntype, h):
            # Apply the `loop_weight` to the input node features, effectively
            # acting as a residual connection. This allows the model to refine
            # node embeddings based on its current features.
            h = h + self.loop_weights[ntype](inputs_dst[ntype])
            if self.activation:
                h = self.activation(h)
            return self.dropout(h)

        # Apply the function defined above for each node type. This will update
        # the node features using the `loop_weights`, apply the activation
        # function and dropout.
        return {ntype: _apply(ntype, h) for ntype, h in hs.items()}


class EntityClassify(nn.Module):
    def __init__(self, graph, in_size, out_size):
        super(EntityClassify, self).__init__()
        self.in_size = in_size
        self.hidden_size = 64
        self.out_size = out_size

        # Generate and sort a list of unique edge types from the input graph.
        # eg. ['writes', 'cites']
        etypes = list(graph.edge_type_to_id.keys())
        etypes = [gb.etype_str_to_tuple(etype)[1] for etype in etypes]
        self.relation_names = etypes
        self.relation_names.sort()
        self.dropout = 0.5
        ntypes = list(graph.node_type_to_id.keys())
        self.layers = nn.ModuleList()

        # First layer: transform input features to hidden features. Use ReLU
        # as the activation function and apply dropout for regularization.
        self.layers.append(
            RelGraphConvLayer(
                self.in_size,
                self.hidden_size,
                ntypes,
                self.relation_names,
                activation=F.relu,
                dropout=self.dropout,
            )
        )

        # Second layer: transform hidden features to output features. No
        # activation function is applied at this stage.
        self.layers.append(
            RelGraphConvLayer(
                self.hidden_size,
                self.out_size,
                ntypes,
                self.relation_names,
                activation=None,
            )
        )

    def reset_parameters(self):
        # Reset the parameters of each layer.
        for layer in self.layers:
            layer.reset_parameters()

    def forward(self, blocks, h):
        for layer, block in zip(self.layers, blocks):
            h = layer(block, h)
        return h


@torch.no_grad()
def evaluate(
    name,
    g,
    model,
    node_embed,
    device,
    item_set,
    features,
    num_workers,
):
    # Switches the model to evaluation mode.
    model.eval()
    category = "paper"
    # An evaluator for the dataset.
    if name == "ogbn-mag":
        evaluator = Evaluator(name=name)
    else:
        evaluator = MAG240MEvaluator()

    num_etype = len(g.num_edges)
    data_loader = create_dataloader(
        name,
        g,
        features,
        item_set,
        device,
        batch_size=4096,
        fanouts=[torch.full((num_etype,), 25), torch.full((num_etype,), 10)],
        shuffle=False,
        num_workers=num_workers,
    )

    # To store the predictions.
    y_hats = list()
    y_true = list()

    for data in tqdm(data_loader, desc="Inference"):
        # Convert MiniBatch to DGL Blocks and move them to the target device.
        blocks = [block.to(device) for block in data.blocks]
        node_features = extract_node_features(
            name, blocks[0], data, node_embed, device
        )

        # Generate predictions.
        logits = model(blocks, node_features)

        logits = logits[category]

        # Apply softmax to the logits and get the prediction by selecting the
        # argmax.
        y_hat = logits.log_softmax(dim=-1).argmax(dim=1, keepdims=True)
        y_hats.append(y_hat.cpu())
        y_true.append(data.labels[category].long())

    y_pred = torch.cat(y_hats, dim=0)
    y_true = torch.cat(y_true, dim=0)
    y_true = torch.unsqueeze(y_true, 1)

    if name == "ogb-lsc-mag240m":
        y_pred = y_pred.view(-1)
        y_true = y_true.view(-1)

    return evaluator.eval({"y_true": y_true, "y_pred": y_pred})["acc"]


def train(
    name,
    g,
    model,
    node_embed,
    optimizer,
    train_set,
    valid_set,
    device,
    features,
    num_workers,
    num_epochs,
):
    print("Start to train...")
    category = "paper"

    num_etype = len(g.num_edges)
    data_loader = create_dataloader(
        name,
        g,
        features,
        train_set,
        device,
        batch_size=1024,
        fanouts=[torch.full((num_etype,), 25), torch.full((num_etype,), 10)],
        shuffle=True,
        num_workers=num_workers,
    )

    # Typically, the best Validation performance is obtained after
    # the 1st or 2nd epoch. This is why the max epoch is set to 3.
    for epoch in range(num_epochs):
        num_train = len(train_set)
        t0 = time.time()
        model.train()

        total_loss = 0

        for data in tqdm(data_loader, desc=f"Training~Epoch {epoch + 1:02d}"):
            # Convert MiniBatch to DGL Blocks and move them to the target
            # device.
            blocks = [block.to(device) for block in data.blocks]

            # Fetch the number of seed nodes in the batch.
            num_seeds = blocks[-1].num_dst_nodes(category)

            # Extract the node features from embedding layer or raw features.
            node_features = extract_node_features(
                name, blocks[0], data, node_embed, device
            )

            # Reset gradients.
            optimizer.zero_grad()
            # Generate predictions.
            logits = model(blocks, node_features)[category]

            y_hat = logits.log_softmax(dim=-1)
            loss = F.nll_loss(y_hat, data.labels[category].long())
            loss.backward()
            optimizer.step()

            total_loss += loss.item() * num_seeds

        t1 = time.time()
        loss = total_loss / num_train

        # Evaluate the model on the val/test set.

        print("Evaluating the model on the validation set.")
        valid_acc = evaluate(
            name, g, model, node_embed, device, valid_set, features, num_workers
        )
        print("Finish evaluating on validation set.")

        print(
            f"Epoch: {epoch + 1:02d}, "
            f"Loss: {loss:.4f}, "
            f"Valid accuracy: {100 * valid_acc:.2f}%, "
            f"Time {t1 - t0:.4f}"
        )


def main(args):
    device = torch.device(
        "cuda" if args.num_gpus > 0 and torch.cuda.is_available() else "cpu"
    )

    # Load dataset.
    (
        g,
        features,
        train_set,
        valid_set,
        test_set,
        num_classes,
    ) = load_dataset(args.dataset)

    # Move the dataset to the pinned memory to enable GPU access.
    if device == torch.device("cuda"):
        g.pin_memory_()
        features.pin_memory_()

    feat_size = features.size("node", "paper", "feat")[0]

    # As `ogb-lsc-mag240m` is a large dataset, features of `author` and
    # `institution` are generated in advance and stored in the feature store.
    # For `ogbn-mag`, we generate the features on the fly.
    embed_layer = None
    if args.dataset == "ogbn-mag":
        # Create the embedding layer and move it to the appropriate device.
        embed_layer = rel_graph_embed(g, feat_size).to(device)
        print(
            "Number of embedding parameters: "
            f"{sum(p.numel() for p in embed_layer.parameters())}"
        )

    # Initialize the entity classification model.
    model = EntityClassify(g, feat_size, num_classes).to(device)

    print(
        "Number of model parameters: "
        f"{sum(p.numel() for p in model.parameters())}"
    )

    if embed_layer is not None:
        embed_layer.reset_parameters()
    model.reset_parameters()

    # `itertools.chain()` is a function in Python's itertools module.
    # It is used to flatten a list of iterables, making them act as
    # one big iterable.
    # In this context, the following code is used to create a single
    # iterable over the parameters of both the model and the embed_layer,
    # which is passed to the optimizer. The optimizer then updates all
    # these parameters during the training process.
    all_params = itertools.chain(
        model.parameters(),
        [] if embed_layer is None else embed_layer.parameters(),
    )
    optimizer = torch.optim.Adam(all_params, lr=0.01)

    expected_max = int(psutil.cpu_count(logical=False))
    if args.num_workers >= expected_max:
        print(
            "[ERROR] You specified num_workers are larger than physical"
            f"cores, please set any number less than {expected_max}",
            file=sys.stderr,
        )

    train(
        args.dataset,
        g,
        model,
        embed_layer,
        optimizer,
        train_set,
        valid_set,
        device,
        features,
        args.num_workers,
        args.num_epochs,
    )

    print("Testing...")
    test_acc = evaluate(
        args.dataset,
        g,
        model,
        embed_layer,
        device,
        test_set,
        features,
        args.num_workers,
    )
    print(f"Test accuracy {test_acc*100:.4f}")


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="GraphBolt RGCN")
    parser.add_argument(
        "--dataset",
        type=str,
        default="ogbn-mag",
        choices=["ogbn-mag", "ogb-lsc-mag240m"],
        help="Dataset name. Possible values: ogbn-mag, ogb-lsc-mag240m",
    )
    parser.add_argument("--num_epochs", type=int, default=3)
    parser.add_argument("--num_workers", type=int, default=0)
    parser.add_argument("--num_gpus", type=int, default=1)

    args = parser.parse_args()

    main(args)