Fix specifying cache factors via env vars with * in name.

docs/sample_config.yaml

@@ -643,6 +643,12 @@ caches:
    # takes priority over setting through the config file.
    # Ex. SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0
    #
+   # Some caches have '*' and other characters that are not
+   # alphanumeric or underscores. These caches can be named with or
+   # without the special characters stripped. For example, to specify
+   # the cache factor for `*stateGroupCache*` via an environment
+   # variable would be `SYNAPSE_CACHE_FACTOR_STATEGROUPCACHE=2`.
+   #
    per_cache_factors:
      #get_users_who_share_room_with_user: 2.0
 

synapse/config/cache.py

@@ -126,6 +126,12 @@ def generate_config_section(self, **kwargs):
            # takes priority over setting through the config file.
            # Ex. SYNAPSE_CACHE_FACTOR_GET_USERS_WHO_SHARE_ROOM_WITH_USER=2.0
            #
+           # Some caches have '*' and other characters that are not
+           # alphanumeric or underscores. These caches can be named with or
+           # without the special characters stripped. For example, to specify
+           # the cache factor for `*stateGroupCache*` via an environment
+           # variable would be `SYNAPSE_CACHE_FACTOR_STATEGROUPCACHE=2`.
+           #
            per_cache_factors:
              #get_users_who_share_room_with_user: 2.0
         """