Memory - GC freeze after startup to save CPU cycles and improve memory management (#4351)

changedetectionio/flask_app.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 
 import flask_login
+import gc
 import hashlib
 import locale
 import os
@@ -1095,6 +1096,15 @@ def changedetection_app(config=None, datastore_o=None):
                        "snapshot reads are NOT confined to the watch data directory. "
                        "This disables protection against path traversal via restored backups (GHSA-8757-69j2-hx56).")
 
+    # Memory/CPU management -
+    # Freeze the startup object graph into the "permanent generation" so that the cyclic
+    # garbage collector never traverses it again, this allows more of the app to swap into 'cold' RAM
+    if 'pytest' not in sys.modules and 'PYTEST_CURRENT_TEST' not in os.environ \
+            and not strtobool(os.getenv('DISABLE_GC_FREEZE', 'no')):
+        gc.collect()
+        gc.freeze()
+        logger.debug(f"GC: froze {gc.get_freeze_count()} startup objects into the permanent generation")
+
     # Start the async workers during app initialization
     # Can be overridden by ENV or use the default settings
     n_workers = int(os.getenv("FETCH_WORKERS", datastore.data['settings']['requests']['workers']))