perf(backend): replace per-file sleep(480) deletion timers with a single janitor thread

backend/routers/sync.py

@@ -61,6 +61,7 @@
 from utils.other.storage import (
     get_syncing_file_temporal_signed_url,
     delete_syncing_temporal_file,
+    schedule_syncing_temporal_file_deletion,
     upload_syncing_temporal_file,
     download_syncing_temporal_file,
     download_audio_chunks_and_merge,
@@ -1016,12 +1017,7 @@ def process_segment(
 ):
     try:
         url = get_syncing_file_temporal_signed_url(path)
-
-        def delete_file():
-            time.sleep(480)
-            delete_syncing_temporal_file(path)
-
-        submit_with_context(storage_executor, delete_file)
+        schedule_syncing_temporal_file_deletion(path)
 
         # Apply user transcription preferences (vocabulary, language, model)
         prefs = transcription_prefs or {}

backend/test.sh

@@ -65,6 +65,7 @@ pytest tests/unit/test_storage_upload_audio_chunk_data_protection.py -v
 pytest tests/unit/test_storage_opus_encoding.py -v
 pytest tests/unit/test_speech_profile_existence.py -v
 pytest tests/unit/test_storage_fanout_limits.py -v
+pytest tests/unit/test_deferred_blob_janitor.py -v
 pytest tests/unit/test_people_conversations_500s.py -v
 pytest tests/unit/test_firestore_read_ops_cache.py -v
 pytest tests/unit/test_ws_auth_handshake.py -v

backend/tests/unit/test_deferred_blob_janitor.py

@@ -0,0 +1,118 @@
+"""
+Tests for the deferred-deletion janitor (utils/other/deferred_delete.py).
+
+One janitor thread + a due-time heap replace the previous per-file
+time.sleep(480) on storage_executor, which parked ~70% of the pool's 128
+threads as idle timers (#7531).
+
+Behavioral tests exercise the real DeferredDeleter (the module has no heavy
+imports). Structural tests verify the four former sleep-sites now use the
+scheduler.
+"""
+
+import os
+import threading
+import time
+
+from utils.other.deferred_delete import DeferredDeleter
+
+
+def _read_source(rel_path):
+    base = os.path.join(os.path.dirname(__file__), '..', '..')
+    with open(os.path.join(base, rel_path), encoding='utf-8') as f:
+        return f.read()
+
+
+def _wait_for(predicate, timeout=2.0):
+    deadline = time.monotonic() + timeout
+    while time.monotonic() < deadline:
+        if predicate():
+            return True
+        time.sleep(0.01)
+    return predicate()
+
+
+class TestDeferredDeleterBehavior:
+    def test_deletes_after_delay(self):
+        deleted = []
+        d = DeferredDeleter(deleted.append)
+        d.schedule('a.wav', 0.05)
+        assert not deleted, 'must not delete before the delay elapses'
+        assert _wait_for(lambda: deleted == ['a.wav'])
+        assert d.pending_count() == 0
+
+    def test_out_of_order_schedules_delete_in_due_order(self):
+        deleted = []
+        lock = threading.Lock()
+
+        def record(path):
+            with lock:
+                deleted.append(path)
+
+        d = DeferredDeleter(record)
+        d.schedule('later.wav', 0.3)
+        d.schedule('sooner.wav', 0.05)
+        assert _wait_for(lambda: len(deleted) == 2)
+        assert deleted == ['sooner.wav', 'later.wav']
+
+    def test_earlier_schedule_interrupts_long_wait(self):
+        """A near-term schedule arriving while the janitor waits on a far-future
+        item must fire on time, not after the far-future wait."""
+        deleted = []
+        d = DeferredDeleter(deleted.append)
+        d.schedule('far.wav', 30)
+        d.schedule('near.wav', 0.05)
+        assert _wait_for(lambda: 'near.wav' in deleted)
+        assert 'far.wav' not in deleted
+        assert d.pending_count() == 1
+
+    def test_failing_delete_does_not_kill_janitor(self):
+        deleted = []
+
+        def flaky(path):
+            if path == 'boom.wav':
+                raise RuntimeError('gcs down')
+            deleted.append(path)
+
+        d = DeferredDeleter(flaky)
+        d.schedule('boom.wav', 0.02)
+        d.schedule('ok.wav', 0.05)
+        assert _wait_for(lambda: deleted == ['ok.wav'])
+
+    def test_single_thread_reused_across_schedules(self):
+        d = DeferredDeleter(lambda path: None)
+        d.schedule('a.wav', 0.01)
+        first_thread = d._thread
+        assert _wait_for(lambda: d.pending_count() == 0)
+        d.schedule('b.wav', 0.01)
+        assert d._thread is first_thread
+        assert _wait_for(lambda: d.pending_count() == 0)
+
+    def test_many_pending_use_one_thread(self):
+        before = threading.active_count()
+        d = DeferredDeleter(lambda path: None)
+        for i in range(200):
+            d.schedule(f'{i}.wav', 60)
+        assert d.pending_count() == 200
+        assert threading.active_count() <= before + 1, '200 pending deletions must cost exactly one thread'
+
+
+class TestSleepPatternRemoved:
+    def test_no_sleep_480_remains_in_backend(self):
+        for rel in ('routers/sync.py', 'utils/chat.py'):
+            assert 'time.sleep(480)' not in _read_source(rel), f'{rel} still parks threads as deletion timers'
+
+    def test_sync_uses_scheduler(self):
+        assert 'schedule_syncing_temporal_file_deletion(path)' in _read_source('routers/sync.py')
+
+    def test_chat_uses_scheduler_at_all_three_sites(self):
+        assert _read_source('utils/chat.py').count('schedule_syncing_temporal_file_deletion(path)') == 3
+
+    def test_storage_defines_scheduler_with_480_default(self):
+        src = _read_source('utils/other/storage.py')
+        assert 'SYNCING_TEMPORAL_DELETE_DELAY_SECONDS = 480' in src
+        assert 'def schedule_syncing_temporal_file_deletion' in src
+
+    def test_precache_sem_restored(self):
+        # 4 → 2 was load-shedding while the pool was full of sleepers (#7526)
+        assert '_PRECACHE_FILE_SEM = threading.BoundedSemaphore(4)' in _read_source('utils/other/storage.py')

backend/tests/unit/test_storage_fanout_limits.py

@@ -90,10 +90,14 @@ def test_precache_file_semaphore_exists(self):
         src = _read_source('utils/other/storage.py')
         assert '_PRECACHE_FILE_SEM' in src
 
-    def test_precache_file_semaphore_is_2(self):
-        """Global precache file semaphore must be BoundedSemaphore(2)."""
+    def test_precache_file_semaphore_is_4(self):
+        """Global precache file semaphore must be BoundedSemaphore(4).
+
+        Was 2 while storage_executor was saturated by per-file sleep(480)
+        deletion timers; restored to 4 once the janitor thread took those
+        over (see test_deferred_blob_janitor.py)."""
         src = _read_source('utils/other/storage.py')
-        assert 'BoundedSemaphore(2)' in src
+        assert '_PRECACHE_FILE_SEM = threading.BoundedSemaphore(4)' in src
 
     def test_precache_conversation_audio_uses_semaphore(self):
         """precache_conversation_audio must gate submissions with _PRECACHE_FILE_SEM."""

backend/tests/unit/test_sync_silent_failure.py

@@ -655,6 +655,7 @@ def setup_class(cls):
         sys.modules['pydub'].AudioSegment = MagicMock()
         sys.modules['utils.other.endpoints'].get_current_user_uid = MagicMock()
         sys.modules['utils.other.storage'].get_syncing_file_temporal_signed_url = MagicMock(return_value='https://fake')
+        sys.modules['utils.other.storage'].schedule_syncing_temporal_file_deletion = MagicMock()
         sys.modules['utils.other.storage'].delete_syncing_temporal_file = MagicMock()
         sys.modules['utils.other.storage'].download_audio_chunks_and_merge = MagicMock()
         sys.modules['utils.other.storage'].get_or_create_merged_audio = MagicMock()
@@ -1050,9 +1051,6 @@ class TestVoiceMessageRuntimeErrorHandling:
     """Tests that voice message functions in utils/chat.py handle RuntimeError from prerecorded."""
 
     _saved_modules = {}
-    _storage_executor = None
-    _storage_executor_had_submit = False
-    _storage_executor_submit = None
     _transcribe_fn = None
     _process_fn = None
     _process_stream_fn = None
@@ -1070,6 +1068,7 @@ def setup_class(cls):
         sys.modules['fal_client'].submit = MagicMock()
         sys.modules['utils.other.endpoints'].timeit = lambda f: f
         sys.modules['utils.other.storage'].get_syncing_file_temporal_signed_url = MagicMock(return_value='https://fake')
+        sys.modules['utils.other.storage'].schedule_syncing_temporal_file_deletion = MagicMock()
         sys.modules['utils.other.storage'].delete_syncing_temporal_file = MagicMock()
         sys.modules['utils.notifications'].send_notification = MagicMock()
         sys.modules['utils.retrieval.graph'].execute_graph_chat = MagicMock()
@@ -1116,26 +1115,12 @@ def setup_class(cls):
         )
         import utils.chat as chat_mod
 
-        cls._storage_executor = chat_mod.storage_executor
-        cls._storage_executor_had_submit = 'submit' in getattr(chat_mod.storage_executor, '__dict__', {})
-        cls._storage_executor_submit = chat_mod.storage_executor.submit
-        chat_mod.storage_executor.submit = MagicMock()
-
         cls._transcribe_fn = staticmethod(transcribe_voice_message_segment)
         cls._process_fn = staticmethod(process_voice_message_segment)
         cls._process_stream_fn = staticmethod(process_voice_message_segment_stream)
 
     @classmethod
     def teardown_class(cls):
-        if cls._storage_executor is not None:
-            if cls._storage_executor_had_submit:
-                cls._storage_executor.submit = cls._storage_executor_submit
-            elif 'submit' in getattr(cls._storage_executor, '__dict__', {}):
-                delattr(cls._storage_executor, 'submit')
-            cls._storage_executor = None
-            cls._storage_executor_submit = None
-            cls._storage_executor_had_submit = False
-
         sys.modules.pop('utils.chat', None)
         for name, orig in cls._saved_modules.items():
             if orig is None:
@@ -1149,7 +1134,7 @@ def test_transcribe_voice_message_handles_runtime_error(self):
         with patch(
             'utils.chat.prerecorded',
             side_effect=RuntimeError('Deepgram transcription failed after 2 attempts: timeout'),
-        ), patch('utils.chat.time.sleep'):
+        ):
             result = self._transcribe_fn('/tmp/test.wav', 'uid', language='en')
 
         assert result == (None, 'en'), f"Expected (None, 'en'), got {result}"
@@ -1159,7 +1144,7 @@ def test_process_voice_message_handles_runtime_error(self):
         with patch(
             'utils.chat.prerecorded',
             side_effect=RuntimeError('Deepgram transcription failed after 2 attempts: timeout'),
-        ), patch('utils.chat.time.sleep'):
+        ):
             result = self._process_fn('/tmp/test.wav', 'uid', language='en')
 
         assert result == [], f"Expected [], got {result}"
@@ -1173,7 +1158,7 @@ async def run():
             with patch(
                 'utils.chat.prerecorded',
                 side_effect=RuntimeError('Deepgram transcription failed after 2 attempts: timeout'),
-            ), patch('utils.chat.time.sleep'):
+            ):
                 async for chunk in self._process_stream_fn('/tmp/test.wav', 'uid', language='en'):
                     chunks.append(chunk)
             return chunks

backend/utils/chat.py

@@ -1,11 +1,8 @@
-import time
 import base64
 import uuid
 from datetime import datetime, timezone
 from typing import AsyncGenerator, List, Optional, Tuple
 
-from utils.executors import storage_executor
-
 import database.chat as chat_db
 import database.notifications as notification_db
 import database.users as user_db
@@ -17,7 +14,7 @@
 from models.transcript_segment import TranscriptSegment
 from utils.conversation_helpers import extract_memory_ids
 from utils.notifications import send_notification
-from utils.other.storage import get_syncing_file_temporal_signed_url, delete_syncing_temporal_file
+from utils.other.storage import get_syncing_file_temporal_signed_url, schedule_syncing_temporal_file_deletion
 from utils.retrieval.graph import execute_graph_chat, execute_graph_chat_stream
 from utils.stt.pre_recorded import (
     get_deepgram_model_for_language,
@@ -63,12 +60,7 @@ def transcribe_voice_message_segment(
     language: str = 'multi',
 ) -> Tuple[Optional[str], Optional[str]]:
     url = get_syncing_file_temporal_signed_url(path)
-
-    def delete_file():
-        time.sleep(480)
-        delete_syncing_temporal_file(path)
-
-    storage_executor.submit(delete_file)
+    schedule_syncing_temporal_file_deletion(path)
 
     if not language:
         language = resolve_voice_message_language(uid, None)
@@ -178,12 +170,7 @@ def process_voice_message_segment(
     language: str = 'multi',
 ):
     url = get_syncing_file_temporal_signed_url(path)
-
-    def delete_file():
-        time.sleep(480)
-        delete_syncing_temporal_file(path)
-
-    storage_executor.submit(delete_file)
+    schedule_syncing_temporal_file_deletion(path)
 
     if not language:
         language = resolve_voice_message_language(uid, None)
@@ -252,12 +239,7 @@ async def process_voice_message_segment_stream(
     language: str = 'multi',
 ) -> AsyncGenerator[str, None]:
     url = get_syncing_file_temporal_signed_url(path)
-
-    def delete_file():
-        time.sleep(480)
-        delete_syncing_temporal_file(path)
-
-    storage_executor.submit(delete_file)
+    schedule_syncing_temporal_file_deletion(path)
 
     if not language:
         language = resolve_voice_message_language(uid, None)

backend/utils/other/deferred_delete.py

@@ -0,0 +1,61 @@
+"""Single-thread deferred-deletion scheduler.
+
+Replaces the previous pattern of parking an executor thread in
+time.sleep(480) per file: at sync volume that kept ~70% of
+storage_executor's 128 threads asleep as ad-hoc timers, which is what
+drove the pool's repeated saturation (#7531). One daemon thread and a
+due-time heap handle any number of pending deletions.
+
+Best-effort by design: pending deletions are lost on process death, same
+as the sleeping threads were; the syncing bucket's lifecycle rule is the
+backstop.
+"""
+
+import heapq
+import logging
+import threading
+import time
+from typing import Callable
+
+logger = logging.getLogger(__name__)
+
+
+class DeferredDeleter:
+    def __init__(self, delete_fn: Callable[[str], None], name: str = 'deferred-delete-janitor'):
+        self._delete_fn = delete_fn
+        self._name = name
+        self._cond = threading.Condition()
+        self._heap = []  # (due_monotonic, seq, path)
+        self._seq = 0
+        self._thread = None
+
+    def schedule(self, path: str, delay_seconds: float) -> None:
+        """Schedule path for deletion after delay_seconds. O(log n), never blocks."""
+        with self._cond:
+            self._seq += 1
+            heapq.heappush(self._heap, (time.monotonic() + delay_seconds, self._seq, path))
+            if self._thread is None:
+                self._thread = threading.Thread(target=self._run, name=self._name, daemon=True)
+                self._thread.start()
+            self._cond.notify()
+
+    def pending_count(self) -> int:
+        with self._cond:
+            return len(self._heap)
+
+    def _run(self):
+        while True:
+            with self._cond:
+                while not self._heap:
+                    self._cond.wait()
+                due, _, path = self._heap[0]
+                delay = due - time.monotonic()
+                if delay > 0:
+                    # A schedule() for an earlier due-time re-notifies and we re-peek
+                    self._cond.wait(timeout=delay)
+                    continue
+                heapq.heappop(self._heap)
+            try:
+                self._delete_fn(path)
+            except Exception as e:
+                logger.warning('deferred delete failed for %s: %s', path, e)