Reload cache factors from disk on SIGHUP

synapse/app/_base.py

@@ -488,15 +488,14 @@ def reload_cache_config(config: HomeServerConfig) -> None:
     # we call this closure.
     assert config is not None
     try:
-        # This will call CacheConfig.read_config, which will automatically call
-        # CacheConfig.resize_all_caches.
         config.reload_config_section("caches")
     except ConfigError as e:
         logger.warning("Failed to reload cache config")
         for f in format_config_error(e):
             logger.warning(f)
     else:
         logger.debug("New cache config: %s", config.caches.__dict__)
+        config.caches.resize_all_caches()
 
 
 def setup_sentry(hs: "HomeServer") -> None:

synapse/app/generic_worker.py

@@ -459,6 +459,7 @@ def start(config_options: List[str]) -> None:
 
     synapse.events.USE_FROZEN_DICTS = config.server.use_frozen_dicts
     synapse.util.caches.TRACK_MEMORY_USAGE = config.caches.track_memory_usage
+    config.caches.resize_all_caches()
 
     if config.server.gc_seconds:
         synapse.metrics.MIN_TIME_BETWEEN_GCS = config.server.gc_seconds

synapse/config/cache.py

@@ -181,6 +181,11 @@ def generate_config_section(self, **kwargs: Any) -> str:
         """
 
     def read_config(self, config: JsonDict, **kwargs: Any) -> None:
+        """Populate this config object with values from `config`.
+
+        This method does NOT resize existing or future caches: use `resize_all_caches`.
+        We use two separate methods so that we can reject bad config before applying it.
+        """
         self.event_cache_size = self.parse_size(
             config.get("event_cache_size", _DEFAULT_EVENT_CACHE_SIZE)
         )
@@ -191,9 +196,6 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         if not isinstance(self.global_factor, (int, float)):
             raise ConfigError("caches.global_factor must be a number.")
 
-        # Set the global one so that it's reflected in new caches
-        properties.default_factor_size = self.global_factor
-
         # Load cache factors from the config
         individual_factors = cache_config.get("per_cache_factors") or {}
         if not isinstance(individual_factors, dict):
@@ -259,19 +261,19 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
             cache_config.get("sync_response_cache_duration", 0)
         )
 
-        # Resize all caches (if necessary) with the new factors we've loaded
-        self.resize_all_caches()
-
-        # Store this function so that it can be called from other classes without
-        # needing an instance of Config
-        properties.resize_all_caches_func = self.resize_all_caches
-
     def resize_all_caches(self) -> None:
-        """Ensure all cache sizes are up to date
+        """Ensure all cache sizes are up-to-date.
 
         For each cache, run the mapped callback function with either
         a specific cache factor or the default, global one.
         """
+        # Set the global factor size, so that new caches are appropriately sized.
+        properties.default_factor_size = self.global_factor
+
+        # Store this function so that it can be called from other classes without
+        # needing an instance of CacheConfig
+        properties.resize_all_caches_func = self.resize_all_caches
+
         # block other threads from modifying _CACHES while we iterate it.
         with _CACHES_LOCK:
             for cache_name, callback in _CACHES.items():