StreamingDataset: Cleanup chunks right away if the dataset doesn't fit within the cache

src/lightning/data/streaming/config.py

@@ -64,7 +64,7 @@ def __init__(
         self._downloader = None
 
         if remote_dir:
-            self._downloader = get_downloader_cls(remote_dir)(remote_dir, cache_dir, self._chunks)
+            self._downloader = get_downloader_cls(remote_dir, cache_dir, self._chunks)
 
     def download_chunk_from_index(self, chunk_index: int) -> None:
         chunk_filename = self._chunks[chunk_index]["filename"]
@@ -85,6 +85,12 @@ def intervals(self) -> List[Tuple[int, int]]:
             raise RuntimeError("The intervals should be defined.")
         return self._intervals
 
+    @property
+    def num_bytes(self) -> int:
+        if self._config is None:
+            raise RuntimeError("The config should be defined.")
+        return sum(c["chunk_bytes"] for c in self._chunks)
+
     @property
     def data_format(self) -> Any:
         if self._config is None:
@@ -146,7 +152,7 @@ def load(
         cache_index_filepath = os.path.join(cache_dir, _INDEX_FILENAME)
 
         if isinstance(remote_dir, str):
-            downloader = get_downloader_cls(remote_dir)(remote_dir, cache_dir, [])
+            downloader = get_downloader_cls(remote_dir, cache_dir, [])
             downloader.download_file(os.path.join(remote_dir, _INDEX_FILENAME), cache_index_filepath)
 
         if not os.path.exists(cache_index_filepath):

src/lightning/data/streaming/downloader.py

@@ -12,8 +12,8 @@
 # limitations under the License.
 import os
 import shutil
-from abc import ABC, abstractmethod
-from typing import Any, Dict, List, Type
+from abc import ABC
+from typing import Any, Dict, List
 from urllib import parse
 
 from lightning.data.streaming.client import S3Client
@@ -31,28 +31,27 @@ def download_chunk_from_index(self, chunk_index: int) -> None:
         remote_chunkpath = os.path.join(self._remote_dir, chunk_filename)
         self.download_file(remote_chunkpath, local_chunkpath)
 
-    @abstractmethod
     def download_file(self, remote_chunkpath: str, local_chunkpath: str) -> None:
         pass
 
 
 class S3Downloader(Downloader):
-    @classmethod
-    def download_file(cls, remote_filepath: str, local_filepath: str) -> None:
+    def __init__(self, remote_dir: str, cache_dir: str, chunks: List[Dict[str, Any]]):
+        super().__init__(remote_dir, cache_dir, chunks)
+        self._client = S3Client()
+
+    def download_file(self, remote_filepath: str, local_filepath: str) -> None:
         obj = parse.urlparse(remote_filepath)
 
         if obj.scheme != "s3":
             raise ValueError(f"Expected obj.scheme to be `s3`, instead, got {obj.scheme} for remote={remote_filepath}")
 
-        # TODO: Add caching to avoid re-creating it
-        s3 = S3Client()
-
         from boto3.s3.transfer import TransferConfig
 
         extra_args: Dict[str, Any] = {}
 
         # Issue: https://github.com/boto/boto3/issues/3113
-        s3.client.download_file(
+        self._client.client.download_file(
             obj.netloc,
             obj.path.lstrip("/"),
             local_filepath,
@@ -62,8 +61,7 @@ def download_file(cls, remote_filepath: str, local_filepath: str) -> None:
 
 
 class LocalDownloader(Downloader):
-    @classmethod
-    def download_file(cls, remote_filepath: str, local_filepath: str) -> None:
+    def download_file(self, remote_filepath: str, local_filepath: str) -> None:
         if not os.path.exists(remote_filepath):
             raise FileNotFoundError(f"The provided remote_path doesn't exist: {remote_filepath}")
         if remote_filepath != local_filepath:
@@ -73,8 +71,8 @@ def download_file(cls, remote_filepath: str, local_filepath: str) -> None:
 _DOWNLOADERS = {"s3://": S3Downloader, "": LocalDownloader}
 
 
-def get_downloader_cls(remote_dir: str) -> Type[Downloader]:
+def get_downloader_cls(remote_dir: str, cache_dir: str, chunks: List[Dict[str, Any]]) -> Downloader:
     for k, cls in _DOWNLOADERS.items():
         if str(remote_dir).startswith(k):
-            return cls
+            return cls(remote_dir, cache_dir, chunks)
     raise ValueError(f"The provided `remote_dir` {remote_dir} doesn't have a downloader associated.")

src/lightning/data/streaming/item_loader.py

@@ -90,7 +90,7 @@ def load_item_from_chunk(self, index: int, chunk_index: int, chunk_filepath: str
             first_exists = exists = os.path.exists(chunk_filepath)
 
             while not exists:
-                sleep(0.01)
+                sleep(0.1)
                 exists = os.path.exists(chunk_filepath)
 
             # Wait to avoid any corruption when the file appears
@@ -166,7 +166,6 @@ def generate_intervals(self) -> List[Tuple[int, int]]:
     def _load_chunk(self, chunk_index: int, chunk_filepath: str) -> None:
         if chunk_index in self._mmaps:
             return
-
         chunk = self._chunks[chunk_index]
 
         # Skip the header
@@ -192,7 +191,7 @@ def load_item_from_chunk(self, index: int, chunk_index: int, chunk_filepath: str
             first_exists = exists = os.path.exists(chunk_filepath)
 
             while not exists:
-                sleep(0.01)
+                sleep(0.1)
                 exists = os.path.exists(chunk_filepath)
 
             # Wait to avoid any corruption when the file appears
@@ -202,7 +201,6 @@ def load_item_from_chunk(self, index: int, chunk_index: int, chunk_filepath: str
             self._chunk_filepaths[chunk_filepath] = True
 
         self._load_chunk(chunk_index, chunk_filepath)
-
         assert self._dtype
 
         buffer: bytes = self._buffers[chunk_index]

src/lightning/data/streaming/reader.py

@@ -18,7 +18,6 @@
 from logging import Logger
 from queue import Empty
 from threading import Thread
-from time import sleep
 from typing import Any, Dict, List, Optional, Tuple, Union
 
 from lightning.data.streaming.config import ChunksConfig
@@ -30,14 +29,18 @@
 
 warnings.filterwarnings("ignore", message=".*The given buffer is not writable.*")
 
-
 if _TORCH_GREATER_EQUAL_2_1_0:
     pass
 
 
 logger = Logger(__name__)
 
 
+_END_TOKEN = "END"
+_DEFAULT_TIMEOUT = 0.1
+_LONG_DEFAULT_TIMEOUT = 5
+
+
 class PrepareChunksThread(Thread):
     """This thread is responsible to download the chunks associated to a given worker."""
 
@@ -59,22 +62,7 @@ def __init__(
         self._parent_cache_dir = os.path.dirname(self._config._cache_dir)
         self._to_download_queue: multiprocessing.Queue = multiprocessing.Queue()
         self._to_delete_queue: multiprocessing.Queue = multiprocessing.Queue()
-        self._to_stop_queue: multiprocessing.Queue = multiprocessing.Queue()
-
-        # populate back the queues with existing items. As they already exists, this is almost a no-op
-        for chunk_index in self._collect_ordered_chunk_indexes_from_cache():
-            self._to_download_queue.put(chunk_index)
-            self._to_delete_queue.put(chunk_index)
-
-    def _collect_ordered_chunk_indexes_from_cache(self) -> List[int]:
-        """List the chunks available in the cache, order them based on their creation time and retrieves their
-        indexes."""
-        chunk_indexes = [
-            [self._config._get_chunk_index_from_filename(f), os.path.getctime(os.path.join(self._config._cache_dir, f))]
-            for f in os.listdir(self._config._cache_dir)
-            if f.endswith(".bin")
-        ]
-        return [int(x[0]) for x in sorted(chunk_indexes, key=lambda x: x[1])]
+        self._delete_chunks_when_processed = self._config.num_bytes > max_cache_size if max_cache_size else False
 
     def download(self, chunk_indexes: List[int]) -> None:
         """Receive the list of the chunk indices to download for the current epoch."""
@@ -93,10 +81,17 @@ def _delete(self, chunk_index: int) -> None:
 
     def stop(self) -> None:
         """Receive the list of the chunk indices to download for the current epoch."""
-        self._to_stop_queue.put(True)
+        self._to_download_queue.put(_END_TOKEN)
 
     def _maybe_delete_chunks(self) -> None:
-        chunk_index = _get_from_queue(self._to_delete_queue)
+        reached_pre_download = self._pre_download_counter == self._max_pre_download
+
+        # we have already pre-downloaded some chunks, we just need to wait for them to be processed.
+        # Note: The timeout here should not be too short. We need to prevent the caller from aggressively
+        # querying the queue and consuming too many CPU cycles.
+        chunk_index = _get_from_queue(
+            self._to_delete_queue, timeout=_LONG_DEFAULT_TIMEOUT if reached_pre_download else _DEFAULT_TIMEOUT
+        )
 
         if chunk_index is not None:
             self._pre_download_counter -= 1
@@ -105,22 +100,30 @@ def _maybe_delete_chunks(self) -> None:
             self._chunks_index_to_be_deleted.append(chunk_index)
 
         # Get the current cache size and decide whether we need to start cleanup. Otherwise, keep track of it
-        while (
-            self._max_cache_size
-            and self._chunks_index_to_be_deleted
-            and _get_folder_size(self._parent_cache_dir) >= self._max_cache_size
-        ):
+        while self._max_cache_size and self._chunks_index_to_be_deleted and self._can_delete_chunk():
             # Delete the oldest chunk
             self._delete(self._chunks_index_to_be_deleted.pop(0))
 
+        return
+
+    def _can_delete_chunk(self) -> bool:
+        if self._delete_chunks_when_processed:
+            return self._pre_download_counter == self._max_pre_download - 1
+        return self._max_cache_size is not None and _get_folder_size(self._parent_cache_dir) >= self._max_cache_size
+
     def _pre_load_chunk(self, chunk_index: int) -> None:
         chunk_filepath, _, _ = self._config[ChunkedIndex(index=-1, chunk_index=chunk_index)]
         self._item_loader.pre_load_chunk(chunk_index, chunk_filepath)
 
     def run(self) -> None:
         while True:
             if self._pre_download_counter <= self._max_pre_download:
+                # Note: The timeout here should not be too short. We need to prevent the caller from aggressively
+                # querying the queue and consuming too many CPU cycles.
                 chunk_index = _get_from_queue(self._to_download_queue)
+                if chunk_index == _END_TOKEN:
+                    return
+
                 if chunk_index is not None:
                     self._config.download_chunk_from_index(chunk_index)
 
@@ -135,11 +138,6 @@ def run(self) -> None:
             if self._max_cache_size:
                 self._maybe_delete_chunks()
 
-            if _get_from_queue(self._to_stop_queue):
-                return
-
-            sleep(0.05)
-
 
 class BinaryReader:
     def __init__(
@@ -238,6 +236,9 @@ def read(self, index: ChunkedIndex) -> Any:
                 assert self._prepare_thread
                 self._prepare_thread.download([index.chunk_index])
 
+            if self._last_chunk_index is None:
+                self._last_chunk_index = index.chunk_index
+
         # Fetch the element
         chunk_filepath, begin, _ = self.config[index]
         item = self._item_loader.load_item_from_chunk(index.index, index.chunk_index, chunk_filepath, begin)
@@ -246,9 +247,10 @@ def read(self, index: ChunkedIndex) -> Any:
         # Otherwise, this could trigger segmentation fault error depending on the item loader used.
         if self._config and self._config._remote_dir and index.chunk_index != self._last_chunk_index:
             assert self._prepare_thread
-            if self._last_chunk_index is not None:
-                # inform the chunk has been completely consumed
-                self._prepare_thread.delete([self._last_chunk_index])
+            assert self._last_chunk_index is not None
+
+            # inform the chunk has been completely consumed
+            self._prepare_thread.delete([self._last_chunk_index])
 
             # track the new chunk index as the latest one
             self._last_chunk_index = index.chunk_index
@@ -294,11 +296,9 @@ def _get_folder_size(path: str) -> int:
     return size
 
 
-def _get_from_queue(queue: multiprocessing.Queue) -> Optional[Any]:
+def _get_from_queue(queue: multiprocessing.Queue, timeout: float = _DEFAULT_TIMEOUT) -> Optional[Any]:
     try:
-        # Note: The timeout here should not be too short. We need to prevent the caller from aggressively
-        #   querying the queue and consuming too many CPU cycles.
-        return queue.get(timeout=0.1)
+        return queue.get(timeout=timeout)
     except Empty:
         pass
     except OSError as e:

tests/tests_data/streaming/test_reader.py

@@ -4,11 +4,12 @@
 import numpy as np
 from lightning.data.streaming.cache import Cache
 from lightning.data.streaming.config import ChunkedIndex
-from lightning.data.streaming.reader import _get_folder_size
+from lightning.data.streaming.item_loader import PyTreeLoader
+from lightning.data.streaming.reader import PrepareChunksThread, _get_folder_size
 from lightning_cloud.resolver import Dir
 
 
-def test_reader_chunk_removal(tmpdir, monkeypatch):
+def test_reader_chunk_removal(tmpdir):
     cache_dir = os.path.join(tmpdir, "cache_dir")
     remote_dir = os.path.join(tmpdir, "remote_dir")
     os.makedirs(cache_dir, exist_ok=True)
@@ -79,3 +80,23 @@ def test_get_folder_size(tmpdir):
     np.save(os.path.join(tmpdir, "array_2.npy"), array)
 
     assert _get_folder_size(tmpdir) == 928 * 2
+
+
+def test_prepare_chunks_thread(tmpdir):
+    cache_dir = os.path.join(tmpdir, "cache_dir")
+    os.makedirs(cache_dir, exist_ok=True)
+    cache = Cache(input_dir=cache_dir, chunk_size=2, max_cache_size=28020)
+
+    for i in range(25):
+        cache[i] = i
+
+    cache.done()
+    cache.merge()
+
+    cache._reader._try_load_config()
+
+    thread = PrepareChunksThread(cache._reader.config, item_loader=PyTreeLoader(), max_cache_size=1)
+    assert thread._delete_chunks_when_processed
+
+    thread = PrepareChunksThread(cache._reader.config, item_loader=PyTreeLoader(), max_cache_size=10000)
+    assert not thread._delete_chunks_when_processed