Reduce CPU/lock contention under concurrent uploads: split cache lock, in-memory stats, dict copy, lightweight request IDs, defaultdict metrics

app/__init__.py

@@ -1,13 +1,13 @@
 from __future__ import annotations
 
 import html as html_module
+import itertools
 import logging
 import mimetypes
 import os
 import shutil
 import sys
 import time
-import uuid
 from logging.handlers import RotatingFileHandler
 from pathlib import Path
 from datetime import timedelta
@@ -39,6 +39,8 @@ from .storage import ObjectStorage, StorageError
 from .version import get_version
 from .website_domains import WebsiteDomainStore
 
+_request_counter = itertools.count(1)
+
 
 def _migrate_config_file(active_path: Path, legacy_paths: List[Path]) -> Path:
     """Migrate config file from legacy locations to the active path.
@@ -481,7 +483,7 @@ def _configure_logging(app: Flask) -> None:
 
     @app.before_request
     def _log_request_start() -> None:
-        g.request_id = uuid.uuid4().hex
+        g.request_id = f"{os.getpid():x}{next(_request_counter):012x}"
         g.request_started_at = time.perf_counter()
         g.request_bytes_in = request.content_length or 0
         app.logger.info(
@@ -616,7 +618,7 @@ def _configure_logging(app: Flask) -> None:
         duration_ms = 0.0
         if hasattr(g, "request_started_at"):
             duration_ms = (time.perf_counter() - g.request_started_at) * 1000
-        request_id = getattr(g, "request_id", uuid.uuid4().hex)
+        request_id = getattr(g, "request_id", f"{os.getpid():x}{next(_request_counter):012x}")
         response.headers.setdefault("X-Request-ID", request_id)
         app.logger.info(
             "Request completed",

app/operation_metrics.py

@@ -5,6 +5,7 @@ import logging
 import random
 import threading
 import time
+from collections import defaultdict
 from dataclasses import dataclass, field
 from datetime import datetime, timezone
 from pathlib import Path
@@ -138,8 +139,8 @@ class OperationMetricsCollector:
         self.interval_seconds = interval_minutes * 60
         self.retention_hours = retention_hours
         self._lock = threading.Lock()
-        self._by_method: Dict[str, OperationStats] = {}
+        self._by_method: Dict[str, OperationStats] = defaultdict(OperationStats)
-        self._by_endpoint: Dict[str, OperationStats] = {}
+        self._by_endpoint: Dict[str, OperationStats] = defaultdict(OperationStats)
         self._by_status_class: Dict[str, int] = {}
         self._error_codes: Dict[str, int] = {}
         self._totals = OperationStats()
@@ -211,8 +212,8 @@ class OperationMetricsCollector:
             self._prune_old_snapshots()
             self._save_history()
 
-            self._by_method.clear()
+            self._by_method = defaultdict(OperationStats)
-            self._by_endpoint.clear()
+            self._by_endpoint = defaultdict(OperationStats)
             self._by_status_class.clear()
             self._error_codes.clear()
             self._totals = OperationStats()
@@ -232,12 +233,7 @@ class OperationMetricsCollector:
         status_class = f"{status_code // 100}xx"
 
         with self._lock:
-            if method not in self._by_method:
-                self._by_method[method] = OperationStats()
             self._by_method[method].record(latency_ms, success, bytes_in, bytes_out)
-
-            if endpoint_type not in self._by_endpoint:
-                self._by_endpoint[endpoint_type] = OperationStats()
             self._by_endpoint[endpoint_type].record(latency_ms, success, bytes_in, bytes_out)
 
             self._by_status_class[status_class] = self._by_status_class.get(status_class, 0) + 1

app/storage.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import copy
 import hashlib
 import json
 import os
@@ -196,7 +195,9 @@ class ObjectStorage:
         self.root.mkdir(parents=True, exist_ok=True)
         self._ensure_system_roots()
         self._object_cache: OrderedDict[str, tuple[Dict[str, ObjectMeta], float, float]] = OrderedDict()
-        self._cache_lock = threading.Lock()
+        self._obj_cache_lock = threading.Lock()
+        self._meta_cache_lock = threading.Lock()
+        self._registry_lock = threading.Lock()
         self._bucket_locks: Dict[str, threading.Lock] = {}
         self._cache_version: Dict[str, int] = {}
         self._bucket_config_cache: Dict[str, tuple[dict[str, Any], float]] = {}
@@ -209,10 +210,14 @@ class ObjectStorage:
         self._meta_read_cache: OrderedDict[tuple, Optional[Dict[str, Any]]] = OrderedDict()
         self._meta_read_cache_max = 2048
         self._cleanup_executor = ThreadPoolExecutor(max_workers=1, thread_name_prefix="ParentCleanup")
+        self._stats_mem: Dict[str, Dict[str, int]] = {}
+        self._stats_serial: Dict[str, int] = {}
+        self._stats_lock = threading.Lock()
+        self._stats_dirty: set[str] = set()
+        self._stats_flush_timer: Optional[threading.Timer] = None
 
     def _get_bucket_lock(self, bucket_id: str) -> threading.Lock:
-        """Get or create a lock for a specific bucket. Reduces global lock contention."""
+        with self._registry_lock:
-        with self._cache_lock:
             if bucket_id not in self._bucket_locks:
                 self._bucket_locks[bucket_id] = threading.Lock()
             return self._bucket_locks[bucket_id]
@@ -260,26 +265,20 @@ class ObjectStorage:
         self._system_bucket_root(bucket_path.name).mkdir(parents=True, exist_ok=True)
 
     def bucket_stats(self, bucket_name: str, cache_ttl: int = 60) -> dict[str, int]:
-        """Return object count and total size for the bucket (cached).
-
-        Args:
-            bucket_name: Name of the bucket
-            cache_ttl: Cache time-to-live in seconds (default 60)
-        """
         bucket_path = self._bucket_path(bucket_name)
         if not bucket_path.exists():
             raise BucketNotFoundError("Bucket does not exist")
 
+        with self._stats_lock:
+            if bucket_name in self._stats_mem:
+                return dict(self._stats_mem[bucket_name])
+
         cache_path = self._system_bucket_root(bucket_name) / "stats.json"
         cached_stats = None
-        cache_fresh = False
 
         if cache_path.exists():
             try:
-                cache_fresh = time.time() - cache_path.stat().st_mtime < cache_ttl
                 cached_stats = json.loads(cache_path.read_text(encoding="utf-8"))
-                if cache_fresh:
-                    return cached_stats
             except (OSError, json.JSONDecodeError):
                 pass
 
@@ -348,6 +347,11 @@ class ObjectStorage:
             "_cache_serial": existing_serial,
         }
 
+        with self._stats_lock:
+            if bucket_name not in self._stats_mem:
+                self._stats_mem[bucket_name] = stats
+                self._stats_serial[bucket_name] = existing_serial
+
         try:
             cache_path.parent.mkdir(parents=True, exist_ok=True)
             cache_path.write_text(json.dumps(stats), encoding="utf-8")
@@ -357,7 +361,10 @@ class ObjectStorage:
         return stats
 
     def _invalidate_bucket_stats_cache(self, bucket_id: str) -> None:
-        """Invalidate the cached bucket statistics."""
+        with self._stats_lock:
+            self._stats_mem.pop(bucket_id, None)
+            self._stats_serial[bucket_id] = self._stats_serial.get(bucket_id, 0) + 1
+            self._stats_dirty.discard(bucket_id)
         cache_path = self._system_bucket_root(bucket_id) / "stats.json"
         try:
             cache_path.unlink(missing_ok=True)
@@ -373,29 +380,48 @@ class ObjectStorage:
         version_bytes_delta: int = 0,
         version_count_delta: int = 0,
     ) -> None:
-        """Incrementally update cached bucket statistics instead of invalidating.
+        with self._stats_lock:
+            if bucket_id not in self._stats_mem:
+                self._stats_mem[bucket_id] = {
+                    "objects": 0, "bytes": 0, "version_count": 0,
+                    "version_bytes": 0, "total_objects": 0, "total_bytes": 0,
+                    "_cache_serial": 0,
+                }
+            data = self._stats_mem[bucket_id]
+            data["objects"] = max(0, data["objects"] + objects_delta)
+            data["bytes"] = max(0, data["bytes"] + bytes_delta)
+            data["version_count"] = max(0, data["version_count"] + version_count_delta)
+            data["version_bytes"] = max(0, data["version_bytes"] + version_bytes_delta)
+            data["total_objects"] = max(0, data["total_objects"] + objects_delta + version_count_delta)
+            data["total_bytes"] = max(0, data["total_bytes"] + bytes_delta + version_bytes_delta)
+            data["_cache_serial"] = data["_cache_serial"] + 1
+            self._stats_serial[bucket_id] = self._stats_serial.get(bucket_id, 0) + 1
+            self._stats_dirty.add(bucket_id)
+            self._schedule_stats_flush()
 
-        This avoids expensive full directory scans on every PUT/DELETE by
+    def _schedule_stats_flush(self) -> None:
-        adjusting the cached values directly. Also signals cross-process cache
+        if self._stats_flush_timer is None or not self._stats_flush_timer.is_alive():
-        invalidation by incrementing _cache_serial.
+            self._stats_flush_timer = threading.Timer(3.0, self._flush_stats)
-        """
+            self._stats_flush_timer.daemon = True
-        cache_path = self._system_bucket_root(bucket_id) / "stats.json"
+            self._stats_flush_timer.start()
-        try:
+
-            cache_path.parent.mkdir(parents=True, exist_ok=True)
+    def _flush_stats(self) -> None:
-            if cache_path.exists():
+        with self._stats_lock:
-                data = json.loads(cache_path.read_text(encoding="utf-8"))
+            dirty = list(self._stats_dirty)
-            else:
+            self._stats_dirty.clear()
-                data = {"objects": 0, "bytes": 0, "version_count": 0, "version_bytes": 0, "total_objects": 0, "total_bytes": 0, "_cache_serial": 0}
+            snapshots = {b: dict(self._stats_mem[b]) for b in dirty if b in self._stats_mem}
-            data["objects"] = max(0, data.get("objects", 0) + objects_delta)
+        for bucket_id, data in snapshots.items():
-            data["bytes"] = max(0, data.get("bytes", 0) + bytes_delta)
+            cache_path = self._system_bucket_root(bucket_id) / "stats.json"
-            data["version_count"] = max(0, data.get("version_count", 0) + version_count_delta)
+            try:
-            data["version_bytes"] = max(0, data.get("version_bytes", 0) + version_bytes_delta)
+                cache_path.parent.mkdir(parents=True, exist_ok=True)
-            data["total_objects"] = max(0, data.get("total_objects", 0) + objects_delta + version_count_delta)
+                cache_path.write_text(json.dumps(data), encoding="utf-8")
-            data["total_bytes"] = max(0, data.get("total_bytes", 0) + bytes_delta + version_bytes_delta)
+            except OSError:
-            data["_cache_serial"] = data.get("_cache_serial", 0) + 1
+                pass
-            cache_path.write_text(json.dumps(data), encoding="utf-8")
+
-        except (OSError, json.JSONDecodeError):
+    def shutdown_stats(self) -> None:
-            pass
+        if self._stats_flush_timer is not None:
+            self._stats_flush_timer.cancel()
+        self._flush_stats()
 
     def delete_bucket(self, bucket_name: str) -> None:
         bucket_path = self._bucket_path(bucket_name)
@@ -413,13 +439,18 @@ class ObjectStorage:
         self._remove_tree(self._system_bucket_root(bucket_id))
         self._remove_tree(self._multipart_bucket_root(bucket_id))
         self._bucket_config_cache.pop(bucket_id, None)
-        with self._cache_lock:
+        with self._obj_cache_lock:
             self._object_cache.pop(bucket_id, None)
             self._cache_version.pop(bucket_id, None)
             self._sorted_key_cache.pop(bucket_id, None)
+        with self._meta_cache_lock:
             stale = [k for k in self._meta_read_cache if k[0] == bucket_id]
             for k in stale:
                 del self._meta_read_cache[k]
+        with self._stats_lock:
+            self._stats_mem.pop(bucket_id, None)
+            self._stats_serial.pop(bucket_id, None)
+            self._stats_dirty.discard(bucket_id)
 
     def list_objects(
         self,
@@ -2131,7 +2162,7 @@ class ObjectStorage:
         now = time.time()
         current_stats_mtime = self._get_cache_marker_mtime(bucket_id)
 
-        with self._cache_lock:
+        with self._obj_cache_lock:
             cached = self._object_cache.get(bucket_id)
             if cached:
                 objects, timestamp, cached_stats_mtime = cached
@@ -2143,7 +2174,7 @@ class ObjectStorage:
         bucket_lock = self._get_bucket_lock(bucket_id)
         with bucket_lock:
             current_stats_mtime = self._get_cache_marker_mtime(bucket_id)
-            with self._cache_lock:
+            with self._obj_cache_lock:
                 cached = self._object_cache.get(bucket_id)
                 if cached:
                     objects, timestamp, cached_stats_mtime = cached
@@ -2154,7 +2185,7 @@ class ObjectStorage:
             objects = self._build_object_cache(bucket_path)
             new_stats_mtime = self._get_cache_marker_mtime(bucket_id)
 
-            with self._cache_lock:
+            with self._obj_cache_lock:
                 current_version = self._cache_version.get(bucket_id, 0)
                 if current_version != cache_version:
                     objects = self._build_object_cache(bucket_path)
@@ -2170,12 +2201,7 @@ class ObjectStorage:
         return objects
 
     def _invalidate_object_cache(self, bucket_id: str) -> None:
-        """Invalidate the object cache and etag index for a bucket.
+        with self._obj_cache_lock:
-
-        Increments version counter to signal stale reads.
-        Cross-process invalidation is handled by checking stats.json mtime.
-        """
-        with self._cache_lock:
             self._object_cache.pop(bucket_id, None)
             self._cache_version[bucket_id] = self._cache_version.get(bucket_id, 0) + 1
 
@@ -2186,22 +2212,10 @@ class ObjectStorage:
             pass
 
     def _get_cache_marker_mtime(self, bucket_id: str) -> float:
-        """Get a cache marker combining serial and object count for cross-process invalidation.
+        return float(self._stats_serial.get(bucket_id, 0))
-
-        Returns a combined value that changes if either _cache_serial or object count changes.
-        This handles cases where the serial was reset but object count differs.
-        """
-        stats_path = self._system_bucket_root(bucket_id) / "stats.json"
-        try:
-            data = json.loads(stats_path.read_text(encoding="utf-8"))
-            serial = data.get("_cache_serial", 0)
-            count = data.get("objects", 0)
-            return float(serial * 1000000 + count)
-        except (OSError, json.JSONDecodeError):
-            return 0
 
     def _update_object_cache_entry(self, bucket_id: str, key: str, meta: Optional[ObjectMeta]) -> None:
-        with self._cache_lock:
+        with self._obj_cache_lock:
             cached = self._object_cache.get(bucket_id)
             if cached:
                 objects, timestamp, stats_mtime = cached
@@ -2359,19 +2373,19 @@ class ObjectStorage:
         return meta_root / parent / "_index.json", entry_name
 
     def _get_meta_index_lock(self, index_path: str) -> threading.Lock:
-        with self._cache_lock:
+        with self._registry_lock:
             if index_path not in self._meta_index_locks:
                 self._meta_index_locks[index_path] = threading.Lock()
             return self._meta_index_locks[index_path]
 
     def _read_index_entry(self, bucket_name: str, key: Path) -> Optional[Dict[str, Any]]:
         cache_key = (bucket_name, str(key))
-        with self._cache_lock:
+        with self._meta_cache_lock:
             hit = self._meta_read_cache.get(cache_key)
             if hit is not None:
                 self._meta_read_cache.move_to_end(cache_key)
                 cached = hit[0]
-                return copy.deepcopy(cached) if cached is not None else None
+                return dict(cached) if cached is not None else None
 
         index_path, entry_name = self._index_file_for_key(bucket_name, key)
         if _HAS_RUST:
@@ -2386,16 +2400,16 @@ class ObjectStorage:
                 except (OSError, json.JSONDecodeError):
                     result = None
 
-        with self._cache_lock:
+        with self._meta_cache_lock:
             while len(self._meta_read_cache) >= self._meta_read_cache_max:
                 self._meta_read_cache.popitem(last=False)
-            self._meta_read_cache[cache_key] = (copy.deepcopy(result) if result is not None else None,)
+            self._meta_read_cache[cache_key] = (dict(result) if result is not None else None,)
 
         return result
 
     def _invalidate_meta_read_cache(self, bucket_name: str, key: Path) -> None:
         cache_key = (bucket_name, str(key))
-        with self._cache_lock:
+        with self._meta_cache_lock:
             self._meta_read_cache.pop(cache_key, None)
 
     def _write_index_entry(self, bucket_name: str, key: Path, entry: Dict[str, Any]) -> None:

app/version.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-APP_VERSION = "0.3.4"
+APP_VERSION = "0.3.5"
 
 
 def get_version() -> str:

tests/conftest.py

@@ -43,6 +43,11 @@ def app(tmp_path: Path):
         }
     )
     yield flask_app
+    storage = flask_app.extensions.get("object_storage")
+    if storage:
+        base = getattr(storage, "storage", storage)
+        if hasattr(base, "shutdown_stats"):
+            base.shutdown_stats()
 
 
 @pytest.fixture()