Support large/infinite training corpora (#7208)

* Support infinite generators for training corpora

Support a training corpus with an infinite generator in the `spacy
train` training loop:

* Revert `create_train_batches` to the state where an infinite generator
can be used as the in the first epoch of exactly one epoch without
resulting in a memory leak (`max_epochs != 1` will still result in a
memory leak)
* Move the shuffling for the first epoch into the corpus reader,
renaming it to `spacy.Corpus.v2`.

* Switch to training option for shuffling in memory

Training loop:

* Add option `training.shuffle_train_corpus_in_memory` that controls
whether the corpus is loaded in memory once and shuffled in the training
loop
  * Revert changes to `create_train_batches` and rename to
`create_train_batches_with_shuffling` for use with `spacy.Corpus.v1` and
a corpus that should be loaded in memory
  * Add `create_train_batches_without_shuffling` for a corpus that
should not be shuffled in the training loop: the corpus is merely
batched during training

Corpus readers:

* Restore `spacy.Corpus.v1`
* Add `spacy.ShuffledCorpus.v1` for a corpus shuffled in memory in the
reader instead of the training loop
  * In combination with `shuffle_train_corpus_in_memory = False`, each
epoch could result in a different augmentation

* Refactor create_train_batches, validation

* Rename config setting to `training.shuffle_train_corpus`
* Refactor to use a single `create_train_batches` method with a
`shuffle` option
* Only validate `get_examples` in initialize step if:
  * labels are required
  * labels are not provided

* Switch back to max_epochs=-1 for streaming train corpus

* Use first 100 examples for stream train corpus init

* Always check validate_get_examples in initialize

spacy/default_config.cfg

@@ -70,6 +70,9 @@ dropout = 0.1
 accumulate_gradient = 1
 # Controls early-stopping. 0 disables early stopping.
 patience = 1600
+# Number of epochs. 0 means unlimited. If >= 0, train corpus is loaded once in
+# memory and shuffled within the training loop. -1 means stream train corpus
+# rather than loading in memory with no shuffling within the training loop.
 max_epochs = 0
 max_steps = 20000
 eval_frequency = 200

spacy/training/corpus.py

@@ -2,6 +2,7 @@ import warnings
 from typing import Union, List, Iterable, Iterator, TYPE_CHECKING, Callable
 from typing import Optional
 from pathlib import Path
+import random
 import srsly
 
 from .. import util
@@ -96,6 +97,7 @@ class Corpus:
         Defaults to 0, which indicates no limit.
     augment (Callable[Example, Iterable[Example]]): Optional data augmentation
         function, to extrapolate additional examples from your annotations.
+    shuffle (bool): Whether to shuffle the examples.
 
     DOCS: https://spacy.io/api/corpus
     """
@@ -108,12 +110,14 @@ class Corpus:
         gold_preproc: bool = False,
         max_length: int = 0,
         augmenter: Optional[Callable] = None,
+        shuffle: bool = False,
     ) -> None:
         self.path = util.ensure_path(path)
         self.gold_preproc = gold_preproc
         self.max_length = max_length
         self.limit = limit
         self.augmenter = augmenter if augmenter is not None else dont_augment
+        self.shuffle = shuffle
 
     def __call__(self, nlp: "Language") -> Iterator[Example]:
         """Yield examples from the data.
@@ -124,6 +128,10 @@ class Corpus:
         DOCS: https://spacy.io/api/corpus#call
         """
         ref_docs = self.read_docbin(nlp.vocab, walk_corpus(self.path, FILE_TYPE))
+        if self.shuffle:
+            ref_docs = list(ref_docs)
+            random.shuffle(ref_docs)
+
         if self.gold_preproc:
             examples = self.make_examples_gold_preproc(nlp, ref_docs)
         else:

spacy/training/initialize.py

@@ -8,6 +8,7 @@ import tarfile
 import gzip
 import zipfile
 import tqdm
+from itertools import islice
 
 from .pretrain import get_tok2vec_ref
 from ..lookups import Lookups
@@ -68,7 +69,11 @@ def init_nlp(config: Config, *, use_gpu: int = -1) -> "Language":
     # Make sure that listeners are defined before initializing further
     nlp._link_components()
     with nlp.select_pipes(disable=[*frozen_components, *resume_components]):
-        nlp.initialize(lambda: train_corpus(nlp), sgd=optimizer)
+        if T["max_epochs"] == -1:
+            logger.debug("Due to streamed train corpus, using only first 100 examples for initialization. If necessary, provide all labels in [initialize]. More info: https://spacy.io/api/cli#init_labels")
+            nlp.initialize(lambda: islice(train_corpus(nlp), 100), sgd=optimizer)
+        else:
+            nlp.initialize(lambda: train_corpus(nlp), sgd=optimizer)
         logger.info(f"Initialized pipeline components: {nlp.pipe_names}")
     # Detect components with listeners that are not frozen consistently
     for name, proc in nlp.pipeline:

spacy/training/loop.py

@@ -78,7 +78,7 @@ def train(
     training_step_iterator = train_while_improving(
         nlp,
         optimizer,
-        create_train_batches(train_corpus(nlp), batcher, T["max_epochs"]),
+        create_train_batches(nlp, train_corpus, batcher, T["max_epochs"]),
         create_evaluation_callback(nlp, dev_corpus, score_weights),
         dropout=T["dropout"],
         accumulate_gradient=T["accumulate_gradient"],
@@ -290,17 +290,22 @@ def create_evaluation_callback(
 
 
 def create_train_batches(
-    iterator: Iterator[Example],
+    nlp: "Language",
+    corpus: Callable[["Language"], Iterable[Example]],
     batcher: Callable[[Iterable[Example]], Iterable[Example]],
     max_epochs: int,
 ):
     epoch = 0
-    examples = list(iterator)
-    if not examples:
-        # Raise error if no data
-        raise ValueError(Errors.E986)
+    if max_epochs >= 0:
+        examples = list(corpus(nlp))
+        if not examples:
+            # Raise error if no data
+            raise ValueError(Errors.E986)
     while max_epochs < 1 or epoch != max_epochs:
-        random.shuffle(examples)
+        if max_epochs >= 0:
+            random.shuffle(examples)
+        else:
+            examples = corpus(nlp)
         for batch in batcher(examples):
             yield epoch, batch
         epoch += 1