Allow configuration of Synapse's cache without using synctl or environment variables (#6391)

docs/sample_config.yaml

@@ -603,6 +603,45 @@ acme:
 
 
 
+## Caching ##
+
+# Caching can be configured through the following options.
+#
+# A cache 'factor' is a multiplier that can be applied to each of
+# Synapse's caches in order to increase or decrease the maximum
+# number of entries that can be stored.
+
+# The number of events to cache in memory. Not affected by
+# caches.global_factor.
+#
+#event_cache_size: 10K
+
+caches:
+   # Controls the global cache factor, which is the default cache factor
+   # for all caches if a specific factor for that cache is not otherwise
+   # set.
+   #
+   # This can also be set by the "SYNAPSE_CACHE_FACTOR" environment
+   # variable. Setting by environment variable takes priority over
+   # setting through the config file.
+   #
+   # Defaults to 0.5, which will half the size of all caches.
+   #
+   #global_factor: 1.0
+
+   # A dictionary of cache name to cache factor for that individual
+   # cache. Overrides the global cache factor for a given cache.
+   #
+   # These can also be set through environment variables comprised
+   # of "SYNAPSE_CACHE_FACTOR_" + the name of the cache in capital
+   # letters and underscores. Setting by environment variable
+   # takes priority over setting through the config file.
+   # Ex. SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0
+   #
+   per_cache_factors:
+     #get_users_who_share_room_with_user: 2.0
+
+
 ## Database ##
 
 # The 'database' setting defines the database that synapse uses to store all of
@@ -646,10 +685,6 @@ database:
   args:
     database: DATADIR/homeserver.db
 
-# Number of events to cache in memory.
-#
-#event_cache_size: 10K
-
 
 ## Logging ##