Exemple #1
0
def do_eval_and_report_stats(
    config: ConfigSchema,
    model: Optional[MultiRelationEmbedder] = None,
    evaluator: Optional[AbstractBatchProcessor] = None,
    subprocess_init: Optional[Callable[[], None]] = None,
) -> Generator[Tuple[Optional[int], Optional[Bucket], Stats], None, None]:
    """Computes eval metrics (mr/mrr/r1/r10/r50) for a checkpoint with trained
       embeddings.
    """
    tag_logs_with_process_name(f"Evaluator")

    if evaluator is None:
        evaluator = RankingEvaluator(
            loss_fn=LOSS_FUNCTIONS.get_class(
                config.loss_fn)(margin=config.margin),
            relation_weights=[
                relation.weight for relation in config.relations
            ],
        )

    if config.verbose > 0:
        import pprint

        pprint.PrettyPrinter().pprint(config.to_dict())

    checkpoint_manager = CheckpointManager(config.checkpoint_path)

    def load_embeddings(entity: EntityName,
                        part: Partition) -> torch.nn.Parameter:
        embs, _ = checkpoint_manager.read(entity, part)
        assert embs.is_shared()
        return torch.nn.Parameter(embs)

    holder = EmbeddingHolder(config)

    num_workers = get_num_workers(config.workers)
    pool = create_pool(num_workers,
                       subprocess_name="EvalWorker",
                       subprocess_init=subprocess_init)

    if model is None:
        model = make_model(config)
    model.share_memory()

    state_dict, _ = checkpoint_manager.maybe_read_model()
    if state_dict is not None:
        model.load_state_dict(state_dict, strict=False)

    model.eval()

    for entity in holder.lhs_unpartitioned_types | holder.rhs_unpartitioned_types:
        embs = load_embeddings(entity, UNPARTITIONED)
        holder.unpartitioned_embeddings[entity] = embs

    all_stats: List[Stats] = []
    for edge_path_idx, edge_path in enumerate(config.edge_paths):
        logger.info(
            f"Starting edge path {edge_path_idx + 1} / {len(config.edge_paths)} "
            f"({edge_path})")
        edge_storage = EDGE_STORAGES.make_instance(edge_path)

        all_edge_path_stats = []
        # FIXME This order assumes higher affinity on the left-hand side, as it's
        # the one changing more slowly. Make this adaptive to the actual affinity.
        for bucket in create_buckets_ordered_lexicographically(
                holder.nparts_lhs, holder.nparts_rhs):
            tic = time.perf_counter()
            # logger.info(f"{bucket}: Loading entities")

            old_parts = set(holder.partitioned_embeddings.keys())
            new_parts = {(e, bucket.lhs)
                         for e in holder.lhs_partitioned_types
                         } | {(e, bucket.rhs)
                              for e in holder.rhs_partitioned_types}
            for entity, part in old_parts - new_parts:
                del holder.partitioned_embeddings[entity, part]
            for entity, part in new_parts - old_parts:
                embs = load_embeddings(entity, part)
                holder.partitioned_embeddings[entity, part] = embs

            model.set_all_embeddings(holder, bucket)

            # logger.info(f"{bucket}: Loading edges")
            edges = edge_storage.load_edges(bucket.lhs, bucket.rhs)
            num_edges = len(edges)

            load_time = time.perf_counter() - tic
            tic = time.perf_counter()
            # logger.info(f"{bucket}: Launching and waiting for workers")
            future_all_bucket_stats = pool.map_async(
                call,
                [
                    partial(
                        process_in_batches,
                        batch_size=config.batch_size,
                        model=model,
                        batch_processor=evaluator,
                        edges=edges[s],
                    ) for s in split_almost_equally(num_edges,
                                                    num_parts=num_workers)
                ],
            )
            all_bucket_stats = get_async_result(future_all_bucket_stats, pool)

            compute_time = time.perf_counter() - tic
            logger.info(
                f"{bucket}: Processed {num_edges} edges in {compute_time:.2g} s "
                f"({num_edges / compute_time / 1e6:.2g}M/sec); "
                f"load time: {load_time:.2g} s")

            total_bucket_stats = Stats.sum(all_bucket_stats)
            all_edge_path_stats.append(total_bucket_stats)
            mean_bucket_stats = total_bucket_stats.average()
            logger.info(
                f"Stats for edge path {edge_path_idx + 1} / {len(config.edge_paths)}, "
                f"bucket {bucket}: {mean_bucket_stats}")

            model.clear_all_embeddings()

            yield edge_path_idx, bucket, mean_bucket_stats

        total_edge_path_stats = Stats.sum(all_edge_path_stats)
        all_stats.append(total_edge_path_stats)
        mean_edge_path_stats = total_edge_path_stats.average()
        logger.info("")
        logger.info(
            f"Stats for edge path {edge_path_idx + 1} / {len(config.edge_paths)}: "
            f"{mean_edge_path_stats}")
        logger.info("")

        yield edge_path_idx, None, mean_edge_path_stats

    mean_stats = Stats.sum(all_stats).average()
    logger.info("")
    logger.info(f"Stats: {mean_stats}")
    logger.info("")

    yield None, None, mean_stats

    pool.close()
    pool.join()
    def __init__(  # noqa
        self,
        config: ConfigSchema,
        model: Optional[MultiRelationEmbedder] = None,
        trainer: Optional[AbstractBatchProcessor] = None,
        evaluator: Optional[AbstractBatchProcessor] = None,
        rank: Rank = SINGLE_TRAINER,
        subprocess_init: Optional[Callable[[], None]] = None,
        stats_handler: StatsHandler = NOOP_STATS_HANDLER,
    ):
        """Each epoch/pass, for each partition pair, loads in embeddings and edgelist
        from disk, runs HOGWILD training on them, and writes partitions back to disk.
        """
        tag_logs_with_process_name(f"Trainer-{rank}")
        self.config = config
        if config.verbose > 0:
            import pprint

            pprint.PrettyPrinter().pprint(config.to_dict())

        logger.info("Loading entity counts...")
        entity_storage = ENTITY_STORAGES.make_instance(config.entity_path)
        entity_counts: Dict[str, List[int]] = {}
        for entity, econf in config.entities.items():
            entity_counts[entity] = []
            for part in range(econf.num_partitions):
                entity_counts[entity].append(entity_storage.load_count(entity, part))

        # Figure out how many lhs and rhs partitions we need
        holder = self.holder = EmbeddingHolder(config)

        logger.debug(
            f"nparts {holder.nparts_lhs} {holder.nparts_rhs} "
            f"types {holder.lhs_partitioned_types} {holder.rhs_partitioned_types}"
        )

        # We know ahead of time that we wil need 1-2 storages for each embedding type,
        # as well as the max size of this storage (num_entities x D).
        # We allocate these storages n advance in `embedding_storage_freelist`.
        # When we need storage for an entity type, we pop it from this free list,
        # and then add it back when we 'delete' the embedding table.
        embedding_storage_freelist: Dict[
            EntityName, Set[torch.FloatStorage]
        ] = defaultdict(set)
        for entity_type, counts in entity_counts.items():
            max_count = max(counts)
            num_sides = (
                (1 if entity_type in holder.lhs_partitioned_types else 0)
                + (1 if entity_type in holder.rhs_partitioned_types else 0)
                + (
                    1
                    if entity_type
                    in (holder.lhs_unpartitioned_types | holder.rhs_unpartitioned_types)
                    else 0
                )
            )
            for _ in range(num_sides):
                embedding_storage_freelist[entity_type].add(
                    allocate_shared_tensor(
                        (max_count, config.entity_dimension(entity_type)),
                        dtype=torch.float,
                    ).storage()
                )

        # create the handlers, threads, etc. for distributed training
        if config.num_machines > 1 or config.num_partition_servers > 0:
            if not 0 <= rank < config.num_machines:
                raise RuntimeError("Invalid rank for trainer")
            if not td.is_available():
                raise RuntimeError(
                    "The installed PyTorch version doesn't provide "
                    "distributed training capabilities."
                )
            ranks = ProcessRanks.from_num_invocations(
                config.num_machines, config.num_partition_servers
            )

            num_ps_groups = config.num_groups_for_partition_server
            groups: List[List[int]] = [ranks.trainers]  # barrier group
            groups += [
                ranks.trainers + ranks.partition_servers
            ] * num_ps_groups  # ps groups
            group_idxs_for_partition_servers = range(1, len(groups))

            if rank == SINGLE_TRAINER:
                logger.info("Setup lock server...")
                start_server(
                    LockServer(
                        num_clients=len(ranks.trainers),
                        nparts_lhs=holder.nparts_lhs,
                        nparts_rhs=holder.nparts_rhs,
                        entities_lhs=holder.lhs_partitioned_types,
                        entities_rhs=holder.rhs_partitioned_types,
                        entity_counts=entity_counts,
                        init_tree=config.distributed_tree_init_order,
                        stats_handler=stats_handler,
                    ),
                    process_name="LockServer",
                    init_method=config.distributed_init_method,
                    world_size=ranks.world_size,
                    server_rank=ranks.lock_server,
                    groups=groups,
                    subprocess_init=subprocess_init,
                )

            self.bucket_scheduler = DistributedBucketScheduler(
                server_rank=ranks.lock_server, client_rank=ranks.trainers[rank]
            )

            logger.info("Setup param server...")
            start_server(
                ParameterServer(num_clients=len(ranks.trainers)),
                process_name=f"ParamS-{rank}",
                init_method=config.distributed_init_method,
                world_size=ranks.world_size,
                server_rank=ranks.parameter_servers[rank],
                groups=groups,
                subprocess_init=subprocess_init,
            )

            parameter_sharer = ParameterSharer(
                process_name=f"ParamC-{rank}",
                client_rank=ranks.parameter_clients[rank],
                all_server_ranks=ranks.parameter_servers,
                init_method=config.distributed_init_method,
                world_size=ranks.world_size,
                groups=groups,
                subprocess_init=subprocess_init,
            )

            if config.num_partition_servers == -1:
                start_server(
                    ParameterServer(
                        num_clients=len(ranks.trainers),
                        group_idxs=group_idxs_for_partition_servers,
                        log_stats=True,
                    ),
                    process_name=f"PartS-{rank}",
                    init_method=config.distributed_init_method,
                    world_size=ranks.world_size,
                    server_rank=ranks.partition_servers[rank],
                    groups=groups,
                    subprocess_init=subprocess_init,
                )

            groups = init_process_group(
                rank=ranks.trainers[rank],
                world_size=ranks.world_size,
                init_method=config.distributed_init_method,
                groups=groups,
            )
            trainer_group, *groups_for_partition_servers = groups
            self.barrier_group = trainer_group

            if len(ranks.partition_servers) > 0:
                partition_client = PartitionClient(
                    ranks.partition_servers,
                    groups=groups_for_partition_servers,
                    log_stats=True,
                )
            else:
                partition_client = None
        else:
            self.barrier_group = None
            self.bucket_scheduler = SingleMachineBucketScheduler(
                holder.nparts_lhs, holder.nparts_rhs, config.bucket_order, stats_handler
            )
            parameter_sharer = None
            partition_client = None
            hide_distributed_logging()

        # fork early for HOGWILD threads
        logger.info("Creating workers...")
        self.num_workers = get_num_workers(config.workers)
        self.pool = create_pool(
            self.num_workers,
            subprocess_name=f"TWorker-{rank}",
            subprocess_init=subprocess_init,
        )

        checkpoint_manager = CheckpointManager(
            config.checkpoint_path,
            rank=rank,
            num_machines=config.num_machines,
            partition_client=partition_client,
            subprocess_name=f"BackgRW-{rank}",
            subprocess_init=subprocess_init,
        )
        self.checkpoint_manager = checkpoint_manager
        checkpoint_manager.register_metadata_provider(ConfigMetadataProvider(config))
        if rank == 0:
            checkpoint_manager.write_config(config)

        num_edge_chunks = get_num_edge_chunks(config)

        self.iteration_manager = IterationManager(
            config.num_epochs,
            config.edge_paths,
            num_edge_chunks,
            iteration_idx=checkpoint_manager.checkpoint_version,
        )
        checkpoint_manager.register_metadata_provider(self.iteration_manager)

        logger.info("Initializing global model...")
        if model is None:
            model = make_model(config)
        model.share_memory()
        loss_fn = LOSS_FUNCTIONS.get_class(config.loss_fn)(margin=config.margin)
        relation_weights = [relation.weight for relation in config.relations]
        if trainer is None:
            trainer = Trainer(
                model_optimizer=make_optimizer(config, model.parameters(), False),
                loss_fn=loss_fn,
                relation_weights=relation_weights,
            )
        if evaluator is None:
            eval_overrides = {}
            if config.eval_num_batch_negs is not None:
                eval_overrides["num_batch_negs"] = config.eval_num_batch_negs
            if config.eval_num_uniform_negs is not None:
                eval_overrides["num_uniform_negs"] = config.eval_num_uniform_negs

            evaluator = RankingEvaluator(
                loss_fn=loss_fn,
                relation_weights=relation_weights,
                overrides=eval_overrides,
            )

        if config.init_path is not None:
            self.loadpath_manager = CheckpointManager(config.init_path)
        else:
            self.loadpath_manager = None

        # load model from checkpoint or loadpath, if available
        state_dict, optim_state = checkpoint_manager.maybe_read_model()
        if state_dict is None and self.loadpath_manager is not None:
            state_dict, optim_state = self.loadpath_manager.maybe_read_model()
        if state_dict is not None:
            model.load_state_dict(state_dict, strict=False)
        if optim_state is not None:
            trainer.model_optimizer.load_state_dict(optim_state)

        logger.debug("Loading unpartitioned entities...")
        for entity in holder.lhs_unpartitioned_types | holder.rhs_unpartitioned_types:
            count = entity_counts[entity][0]
            s = embedding_storage_freelist[entity].pop()
            dimension = config.entity_dimension(entity)
            embs = torch.FloatTensor(s).view(-1, dimension)[:count]
            embs, optimizer = self._load_embeddings(entity, UNPARTITIONED, out=embs)
            holder.unpartitioned_embeddings[entity] = embs
            trainer.unpartitioned_optimizers[entity] = optimizer

        # start communicating shared parameters with the parameter server
        if parameter_sharer is not None:
            shared_parameters: Set[int] = set()
            for name, param in model.named_parameters():
                if id(param) in shared_parameters:
                    continue
                shared_parameters.add(id(param))
                key = f"model.{name}"
                logger.info(
                    f"Adding {key} ({param.numel()} params) to parameter server"
                )
                parameter_sharer.set_param(key, param.data)
            for entity, embs in holder.unpartitioned_embeddings.items():
                key = f"entity.{entity}"
                logger.info(f"Adding {key} ({embs.numel()} params) to parameter server")
                parameter_sharer.set_param(key, embs.data)

        # store everything in self
        self.model = model
        self.trainer = trainer
        self.evaluator = evaluator
        self.rank = rank
        self.entity_counts = entity_counts
        self.embedding_storage_freelist = embedding_storage_freelist
        self.stats_handler = stats_handler

        self.strict = False
Exemple #3
0
def train_and_report_stats(
    config: ConfigSchema,
    model: Optional[MultiRelationEmbedder] = None,
    trainer: Optional[AbstractBatchProcessor] = None,
    evaluator: Optional[AbstractBatchProcessor] = None,
    rank: Rank = RANK_ZERO,
    subprocess_init: Optional[Callable[[], None]] = None,
) -> Generator[Tuple[int, Optional[Stats], Stats, Optional[Stats]], None, None]:
    """Each epoch/pass, for each partition pair, loads in embeddings and edgelist
    from disk, runs HOGWILD training on them, and writes partitions back to disk.
    """
    tag_logs_with_process_name(f"Trainer-{rank}")

    if config.verbose > 0:
        import pprint
        pprint.PrettyPrinter().pprint(config.to_dict())

    logger.info("Loading entity counts...")
    entity_storage = ENTITY_STORAGES.make_instance(config.entity_path)
    entity_counts: Dict[str, List[int]] = {}
    for entity, econf in config.entities.items():
        entity_counts[entity] = []
        for part in range(econf.num_partitions):
            entity_counts[entity].append(entity_storage.load_count(entity, part))

    # Figure out how many lhs and rhs partitions we need
    holder = EmbeddingHolder(config)
    logger.debug(
        f"nparts {holder.nparts_lhs} {holder.nparts_rhs} "
        f"types {holder.lhs_partitioned_types} {holder.rhs_partitioned_types}")
    total_buckets = holder.nparts_lhs * holder.nparts_rhs

    sync: AbstractSynchronizer
    bucket_scheduler: AbstractBucketScheduler
    parameter_sharer: Optional[ParameterSharer]
    partition_client: Optional[PartitionClient]
    if config.num_machines > 1:
        if not 0 <= rank < config.num_machines:
            raise RuntimeError("Invalid rank for trainer")
        if not td.is_available():
            raise RuntimeError("The installed PyTorch version doesn't provide "
                               "distributed training capabilities.")
        ranks = ProcessRanks.from_num_invocations(
            config.num_machines, config.num_partition_servers)

        if rank == RANK_ZERO:
            logger.info("Setup lock server...")
            start_server(
                LockServer(
                    num_clients=len(ranks.trainers),
                    nparts_lhs=holder.nparts_lhs,
                    nparts_rhs=holder.nparts_rhs,
                    entities_lhs=holder.lhs_partitioned_types,
                    entities_rhs=holder.rhs_partitioned_types,
                    entity_counts=entity_counts,
                    init_tree=config.distributed_tree_init_order,
                ),
                process_name="LockServer",
                init_method=config.distributed_init_method,
                world_size=ranks.world_size,
                server_rank=ranks.lock_server,
                groups=[ranks.trainers],
                subprocess_init=subprocess_init,
            )

        bucket_scheduler = DistributedBucketScheduler(
            server_rank=ranks.lock_server,
            client_rank=ranks.trainers[rank],
        )

        logger.info("Setup param server...")
        start_server(
            ParameterServer(num_clients=len(ranks.trainers)),
            process_name=f"ParamS-{rank}",
            init_method=config.distributed_init_method,
            world_size=ranks.world_size,
            server_rank=ranks.parameter_servers[rank],
            groups=[ranks.trainers],
            subprocess_init=subprocess_init,
        )

        parameter_sharer = ParameterSharer(
            process_name=f"ParamC-{rank}",
            client_rank=ranks.parameter_clients[rank],
            all_server_ranks=ranks.parameter_servers,
            init_method=config.distributed_init_method,
            world_size=ranks.world_size,
            groups=[ranks.trainers],
            subprocess_init=subprocess_init,
        )

        if config.num_partition_servers == -1:
            start_server(
                ParameterServer(num_clients=len(ranks.trainers), log_stats=True),
                process_name=f"PartS-{rank}",
                init_method=config.distributed_init_method,
                world_size=ranks.world_size,
                server_rank=ranks.partition_servers[rank],
                groups=[ranks.trainers],
                subprocess_init=subprocess_init,
            )

        if len(ranks.partition_servers) > 0:
            partition_client = PartitionClient(ranks.partition_servers, log_stats=True)
        else:
            partition_client = None

        groups = init_process_group(
            rank=ranks.trainers[rank],
            world_size=ranks.world_size,
            init_method=config.distributed_init_method,
            groups=[ranks.trainers],
        )
        trainer_group, = groups
        sync = DistributedSynchronizer(trainer_group)

    else:
        sync = DummySynchronizer()
        bucket_scheduler = SingleMachineBucketScheduler(
            holder.nparts_lhs, holder.nparts_rhs, config.bucket_order)
        parameter_sharer = None
        partition_client = None
        hide_distributed_logging()

    # fork early for HOGWILD threads
    logger.info("Creating workers...")
    num_workers = get_num_workers(config.workers)
    pool = create_pool(
        num_workers,
        subprocess_name=f"TWorker-{rank}",
        subprocess_init=subprocess_init,
    )

    def make_optimizer(params: Iterable[torch.nn.Parameter], is_emb: bool) -> Optimizer:
        params = list(params)
        if len(params) == 0:
            optimizer = DummyOptimizer()
        elif is_emb:
            optimizer = RowAdagrad(params, lr=config.lr)
        else:
            if config.relation_lr is not None:
                lr = config.relation_lr
            else:
                lr = config.lr
            optimizer = Adagrad(params, lr=lr)
        optimizer.share_memory()
        return optimizer

    # background_io is only supported in single-machine mode
    background_io = config.background_io and config.num_machines == 1

    checkpoint_manager = CheckpointManager(
        config.checkpoint_path,
        background=background_io,
        rank=rank,
        num_machines=config.num_machines,
        partition_client=partition_client,
        subprocess_name=f"BackgRW-{rank}",
        subprocess_init=subprocess_init,
    )
    checkpoint_manager.register_metadata_provider(ConfigMetadataProvider(config))
    if rank == 0:
        checkpoint_manager.write_config(config)

    if config.num_edge_chunks is not None:
        num_edge_chunks = config.num_edge_chunks
    else:
        num_edge_chunks = get_num_edge_chunks(
            config.edge_paths, config.max_edges_per_chunk)
    iteration_manager = IterationManager(
        config.num_epochs, config.edge_paths, num_edge_chunks,
        iteration_idx=checkpoint_manager.checkpoint_version)
    checkpoint_manager.register_metadata_provider(iteration_manager)

    if config.init_path is not None:
        loadpath_manager = CheckpointManager(config.init_path)
    else:
        loadpath_manager = None

    def load_embeddings(
        entity: EntityName,
        part: Partition,
        strict: bool = False,
        force_dirty: bool = False,
    ) -> Tuple[torch.nn.Parameter, Adagrad]:
        if strict:
            embs, optim_state = checkpoint_manager.read(entity, part,
                                                        force_dirty=force_dirty)
        else:
            # Strict is only false during the first iteration, because in that
            # case the checkpoint may not contain any data (unless a previous
            # run was resumed) so we fall back on initial values.
            embs, optim_state = checkpoint_manager.maybe_read(entity, part,
                                                              force_dirty=force_dirty)
            if embs is None and loadpath_manager is not None:
                embs, optim_state = loadpath_manager.maybe_read(entity, part)
            if embs is None:
                embs, optim_state = init_embs(entity, entity_counts[entity][part],
                                              config.dimension, config.init_scale)
        assert embs.is_shared()
        embs = torch.nn.Parameter(embs)
        optimizer = make_optimizer([embs], True)
        if optim_state is not None:
            optimizer.load_state_dict(optim_state)
        return embs, optimizer

    logger.info("Initializing global model...")

    if model is None:
        model = make_model(config)
    model.share_memory()
    if trainer is None:
        trainer = Trainer(
            model_optimizer=make_optimizer(model.parameters(), False),
            loss_fn=config.loss_fn,
            margin=config.margin,
            relations=config.relations,
        )
    if evaluator is None:
        evaluator = TrainingRankingEvaluator(
            override_num_batch_negs=config.eval_num_batch_negs,
            override_num_uniform_negs=config.eval_num_uniform_negs,
        )
    eval_batch_size = round_up_to_nearest_multiple(config.batch_size, config.eval_num_batch_negs)

    state_dict, optim_state = checkpoint_manager.maybe_read_model()

    if state_dict is None and loadpath_manager is not None:
        state_dict, optim_state = loadpath_manager.maybe_read_model()
    if state_dict is not None:
        model.load_state_dict(state_dict, strict=False)
    if optim_state is not None:
        trainer.model_optimizer.load_state_dict(optim_state)

    logger.debug("Loading unpartitioned entities...")
    for entity in holder.lhs_unpartitioned_types | holder.rhs_unpartitioned_types:
        embs, optimizer = load_embeddings(entity, Partition(0))
        holder.unpartitioned_embeddings[entity] = embs
        trainer.unpartitioned_optimizers[entity] = optimizer

    # start communicating shared parameters with the parameter server
    if parameter_sharer is not None:
        shared_parameters: Set[int] = set()
        for name, param in model.named_parameters():
            if id(param) in shared_parameters:
                continue
            shared_parameters.add(id(param))
            key = f"model.{name}"
            logger.info(f"Adding {key} ({param.numel()} params) to parameter server")
            parameter_sharer.set_param(key, param.data)
        for entity, embs in holder.unpartitioned_embeddings.items():
            key = f"entity.{entity}"
            logger.info(f"Adding {key} ({embs.numel()} params) to parameter server")
            parameter_sharer.set_param(key, embs.data)

    strict = False

    def swap_partitioned_embeddings(
        old_b: Optional[Bucket],
        new_b: Optional[Bucket],
        old_stats: Optional[BucketStats],
    ) -> int:
        io_bytes = 0
        logger.info(f"Swapping partitioned embeddings {old_b} {new_b}")

        old_parts: Set[Tuple[EntityName, Partition]] = set()
        if old_b is not None:
            old_parts.update((e, old_b.lhs) for e in holder.lhs_partitioned_types)
            old_parts.update((e, old_b.rhs) for e in holder.rhs_partitioned_types)
        new_parts: Set[Tuple[EntityName, Partition]] = set()
        if new_b is not None:
            new_parts.update((e, new_b.lhs) for e in holder.lhs_partitioned_types)
            new_parts.update((e, new_b.rhs) for e in holder.rhs_partitioned_types)

        assert old_parts == holder.partitioned_embeddings.keys()

        if old_b is not None:
            if old_stats is None:
                raise TypeError("Got old bucket but not its stats")
            logger.info("Saving partitioned embeddings to checkpoint")
            for entity, part in old_parts - new_parts:
                logger .debug(f"Saving ({entity} {part})")
                embs = holder.partitioned_embeddings.pop((entity, part))
                optimizer = trainer.partitioned_optimizers.pop((entity, part))
                checkpoint_manager.write(
                    entity, part,
                    embs.detach(), OptimizerStateDict(optimizer.state_dict()))
                io_bytes += embs.numel() * embs.element_size()  # ignore optim state
                # these variables are holding large objects; let them be freed
                del embs
                del optimizer

            bucket_scheduler.release_bucket(old_b, old_stats)

        if new_b is not None:
            logger.info("Loading partitioned embeddings from checkpoint")
            for entity, part in new_parts - old_parts:
                logger.debug(f"Loading ({entity} {part})")
                force_dirty = bucket_scheduler.check_and_set_dirty(entity, part)
                embs, optimizer = load_embeddings(
                    entity, part, strict=strict, force_dirty=force_dirty)
                holder.partitioned_embeddings[entity, part] = embs
                trainer.partitioned_optimizers[entity, part] = optimizer
                io_bytes += embs.numel() * embs.element_size()  # ignore optim state

        assert new_parts == holder.partitioned_embeddings.keys()

        return io_bytes

    if rank == RANK_ZERO:
        for stats_dict in checkpoint_manager.maybe_read_stats():
            index: int = stats_dict["index"]
            stats: Stats = Stats.from_dict(stats_dict["stats"])
            eval_stats_before: Optional[Stats] = None
            if "eval_stats_before" in stats_dict:
                eval_stats_before = Stats.from_dict(stats_dict["eval_stats_before"])
            eval_stats_after: Optional[Stats] = None
            if "eval_stats_after" in stats_dict:
                eval_stats_after = Stats.from_dict(stats_dict["eval_stats_after"])
            yield (index, eval_stats_before, stats, eval_stats_after)

    # Start of the main training loop.
    for epoch_idx, edge_path_idx, edge_chunk_idx in iteration_manager:
        logger.info(
            f"Starting epoch {epoch_idx + 1} / {iteration_manager.num_epochs}, "
            f"edge path {edge_path_idx + 1} / {iteration_manager.num_edge_paths}, "
            f"edge chunk {edge_chunk_idx + 1} / {iteration_manager.num_edge_chunks}")
        edge_storage = EDGE_STORAGES.make_instance(iteration_manager.edge_path)
        logger.info(f"Edge path: {iteration_manager.edge_path}")

        sync.barrier()
        dist_logger.info("Lock client new epoch...")
        bucket_scheduler.new_pass(is_first=iteration_manager.iteration_idx == 0)
        sync.barrier()

        remaining = total_buckets
        cur_b: Optional[Bucket] = None
        cur_stats: Optional[BucketStats] = None
        while remaining > 0:
            old_b: Optional[Bucket] = cur_b
            old_stats: Optional[BucketStats] = cur_stats
            io_time = 0.
            io_bytes = 0
            cur_b, remaining = bucket_scheduler.acquire_bucket()
            logger.info(f"still in queue: {remaining}")
            if cur_b is None:
                cur_stats = None
                if old_b is not None:
                    # if you couldn't get a new pair, release the lock
                    # to prevent a deadlock!
                    tic = time.time()
                    io_bytes += swap_partitioned_embeddings(old_b, None, old_stats)
                    io_time += time.time() - tic
                time.sleep(1)  # don't hammer td
                continue

            bucket_logger = BucketLogger(logger, bucket=cur_b)

            tic = time.time()

            io_bytes += swap_partitioned_embeddings(old_b, cur_b, old_stats)

            model.set_all_embeddings(holder, cur_b)

            current_index = \
                (iteration_manager.iteration_idx + 1) * total_buckets - remaining

            next_b = bucket_scheduler.peek()
            if next_b is not None and background_io:
                # Ensure the previous bucket finished writing to disk.
                checkpoint_manager.wait_for_marker(current_index - 1)

                bucket_logger.debug("Prefetching")
                for entity in holder.lhs_partitioned_types:
                    checkpoint_manager.prefetch(entity, next_b.lhs)
                for entity in holder.rhs_partitioned_types:
                    checkpoint_manager.prefetch(entity, next_b.rhs)

                checkpoint_manager.record_marker(current_index)

            bucket_logger.debug("Loading edges")
            edges = edge_storage.load_chunk_of_edges(
                cur_b.lhs, cur_b.rhs, edge_chunk_idx, iteration_manager.num_edge_chunks)
            num_edges = len(edges)
            # this might be off in the case of tensorlist or extra edge fields
            io_bytes += edges.lhs.tensor.numel() * edges.lhs.tensor.element_size()
            io_bytes += edges.rhs.tensor.numel() * edges.rhs.tensor.element_size()
            io_bytes += edges.rel.numel() * edges.rel.element_size()

            bucket_logger.debug("Shuffling edges")
            # Fix a seed to get the same permutation every time; have it
            # depend on all and only what affects the set of edges.
            g = torch.Generator()
            g.manual_seed(hash((edge_path_idx, edge_chunk_idx, cur_b.lhs, cur_b.rhs)))

            num_eval_edges = int(num_edges * config.eval_fraction)
            if num_eval_edges > 0:
                edge_perm = torch.randperm(num_edges, generator=g)
                eval_edge_perm = edge_perm[-num_eval_edges:]
                num_edges -= num_eval_edges
                edge_perm = edge_perm[torch.randperm(num_edges)]
            else:
                edge_perm = torch.randperm(num_edges)

            # HOGWILD evaluation before training
            eval_stats_before: Optional[Stats] = None
            if num_eval_edges > 0:
                bucket_logger.debug("Waiting for workers to perform evaluation")
                future_all_eval_stats_before = pool.map_async(call, [
                    partial(
                        process_in_batches,
                        batch_size=eval_batch_size,
                        model=model,
                        batch_processor=evaluator,
                        edges=edges,
                        indices=eval_edge_perm[s],
                    )
                    for s in split_almost_equally(eval_edge_perm.size(0),
                                                  num_parts=num_workers)
                ])
                all_eval_stats_before = \
                    get_async_result(future_all_eval_stats_before, pool)
                eval_stats_before = Stats.sum(all_eval_stats_before).average()
                bucket_logger.info(f"Stats before training: {eval_stats_before}")

            io_time += time.time() - tic
            tic = time.time()
            # HOGWILD training
            bucket_logger.debug("Waiting for workers to perform training")
            # FIXME should we only delay if iteration_idx == 0?
            future_all_stats = pool.map_async(call, [
                partial(
                    process_in_batches,
                    batch_size=config.batch_size,
                    model=model,
                    batch_processor=trainer,
                    edges=edges,
                    indices=edge_perm[s],
                    delay=config.hogwild_delay if epoch_idx == 0 and rank > 0 else 0,
                )
                for rank, s in enumerate(split_almost_equally(edge_perm.size(0),
                                                              num_parts=num_workers))
            ])
            all_stats = get_async_result(future_all_stats, pool)
            stats = Stats.sum(all_stats).average()
            compute_time = time.time() - tic

            bucket_logger.info(
                f"bucket {total_buckets - remaining} / {total_buckets} : "
                f"Processed {num_edges} edges in {compute_time:.2f} s "
                f"( {num_edges / compute_time / 1e6:.2g} M/sec ); "
                f"io: {io_time:.2f} s ( {io_bytes / io_time / 1e6:.2f} MB/sec )")
            bucket_logger.info(f"{stats}")

            # HOGWILD eval after training
            eval_stats_after: Optional[Stats] = None
            if num_eval_edges > 0:
                bucket_logger.debug("Waiting for workers to perform evaluation")
                future_all_eval_stats_after = pool.map_async(call, [
                    partial(
                        process_in_batches,
                        batch_size=eval_batch_size,
                        model=model,
                        batch_processor=evaluator,
                        edges=edges,
                        indices=eval_edge_perm[s],
                    )
                    for s in split_almost_equally(eval_edge_perm.size(0),
                                                  num_parts=num_workers)
                ])
                all_eval_stats_after = \
                    get_async_result(future_all_eval_stats_after, pool)
                eval_stats_after = Stats.sum(all_eval_stats_after).average()
                bucket_logger.info(f"Stats after training: {eval_stats_after}")

            model.clear_all_embeddings()

            yield current_index, eval_stats_before, stats, eval_stats_after

            cur_stats = BucketStats(
                lhs_partition=cur_b.lhs,
                rhs_partition=cur_b.rhs,
                index=current_index,
                train=stats,
                eval_before=eval_stats_before,
                eval_after=eval_stats_after,
            )

        swap_partitioned_embeddings(cur_b, None, cur_stats)

        # Distributed Processing: all machines can leave the barrier now.
        sync.barrier()

        # Preserving a checkpoint requires two steps:
        # - create a snapshot (w/ symlinks) after it's first written;
        # - don't delete it once the following one is written.
        # These two happen in two successive iterations of the main loop: the
        # one just before and the one just after the epoch boundary.
        preserve_old_checkpoint = should_preserve_old_checkpoint(
            iteration_manager, config.checkpoint_preservation_interval)
        preserve_new_checkpoint = should_preserve_old_checkpoint(
            iteration_manager + 1, config.checkpoint_preservation_interval)

        # Write metadata: for multiple machines, write from rank-0
        logger.info(
            f"Finished epoch {epoch_idx + 1} / {iteration_manager.num_epochs}, "
            f"edge path {edge_path_idx + 1} / {iteration_manager.num_edge_paths}, "
            f"edge chunk {edge_chunk_idx + 1} / {iteration_manager.num_edge_chunks}")
        if rank == 0:
            for entity, econfig in config.entities.items():
                if econfig.num_partitions == 1:
                    embs = holder.unpartitioned_embeddings[entity]
                    optimizer = trainer.unpartitioned_optimizers[entity]
                    checkpoint_manager.write(
                        entity, Partition(0),
                        embs.detach(), OptimizerStateDict(optimizer.state_dict()))

            logger.info("Writing the metadata")
            state_dict: ModuleStateDict = ModuleStateDict(model.state_dict())
            checkpoint_manager.write_model(
                state_dict, OptimizerStateDict(trainer.model_optimizer.state_dict()))

            logger.info("Writing the training stats")
            all_stats_dicts: List[Dict[...]] = []
            for stats in bucket_scheduler.get_stats_for_pass():
                stats_dict = {
                    "epoch_idx": epoch_idx,
                    "edge_path_idx": edge_path_idx,
                    "edge_chunk_idx": edge_chunk_idx,
                    "lhs_partition": stats.lhs_partition,
                    "rhs_partition": stats.rhs_partition,
                    "index": stats.index,
                    "stats": stats.train.to_dict(),
                }
                if stats.eval_before is not None:
                    stats_dict["eval_stats_before"] = stats.eval_before.to_dict()
                if stats.eval_after is not None:
                    stats_dict["eval_stats_after"] = stats.eval_after.to_dict()
                all_stats_dicts.append(stats_dict)
            checkpoint_manager.append_stats(all_stats_dicts)

        logger.info("Writing the checkpoint")
        checkpoint_manager.write_new_version(config)

        dist_logger.info("Waiting for other workers to write their parts of the checkpoint")
        sync.barrier()
        dist_logger.info("All parts of the checkpoint have been written")

        logger.info("Switching to the new checkpoint version")
        checkpoint_manager.switch_to_new_version()

        dist_logger.info("Waiting for other workers to switch to the new checkpoint version")
        sync.barrier()
        dist_logger.info("All workers have switched to the new checkpoint version")

        # After all the machines have finished committing
        # checkpoints, we either remove the old checkpoints
        # or we preserve it
        if preserve_new_checkpoint:
            # Add 1 so the index is a multiple of the interval, it looks nicer.
            checkpoint_manager.preserve_current_version(config, epoch_idx + 1)
        if not preserve_old_checkpoint:
            checkpoint_manager.remove_old_version(config)

        # now we're sure that all partition files exist,
        # so be strict about loading them
        strict = True

    # quiescence
    pool.close()
    pool.join()

    sync.barrier()

    checkpoint_manager.close()
    if loadpath_manager is not None:
        loadpath_manager.close()

    # FIXME join distributed workers (not really necessary)

    logger.info("Exiting")