Optionally track memory usage of each LruCache (#9881)

This will double count slightly in the presence of interned strings. It's off by default as it can consume a lot of resources.

1 files changed, 11 insertions, 0 deletions

diff --git a/synapse/config/cache.py b/synapse/config/cache.py
index 41b9b3f51f..91165ee1ce 100644
--- a/synapse/config/cache.py
+++ b/synapse/config/cache.py
@@ -17,6 +17,8 @@ import re
 import threading
 from typing import Callable, Dict
 
+from synapse.python_dependencies import DependencyException, check_requirements
+
 from ._base import Config, ConfigError
 
 # The prefix for all cache factor-related environment variables
@@ -189,6 +191,15 @@ class CacheConfig(Config):
                 )
             self.cache_factors[cache] = factor
 
+        self.track_memory_usage = cache_config.get("track_memory_usage", False)
+        if self.track_memory_usage:
+            try:
+                check_requirements("cache_memory")
+            except DependencyException as e:
+                raise ConfigError(
+                    e.message  # noqa: B306, DependencyException.message is a property
+                )
+
         # Resize all caches (if necessary) with the new factors we've loaded
         self.resize_all_caches()