Document that media purging will be done by the media worker

docs/sample_config.yaml

@@ -1045,12 +1045,16 @@ media_store_path: "DATADIR/media_store"
 
 # Configure media retention settings. Media will be purged if it
 # has not been accessed in at least this amount of time. If the
-# media has never been access, the media's creation time is used
+# media has never been accessed, the media's creation time is used
 # instead. Both thumbnails and the original media will be removed.
 #
 # Media is 'accessed' when loaded in a room in a client, or
 # otherwise downloaded by a local or remote user.
 #
+# Purging the media will be the carried out by the media worker
+# (whichever worker has the 'enable_media_repo' homeserver config
+# option enabled). This may be the main process.
+#
 media_retention:
     # Whether media retention settings should apply. Defaults to
     # false.

synapse/config/repository.py

@@ -308,12 +308,16 @@ def generate_config_section(self, data_dir_path: str, **kwargs: Any) -> str:
 
         # Configure media retention settings. Media will be purged if it
         # has not been accessed in at least this amount of time. If the
-        # media has never been access, the media's creation time is used
+        # media has never been accessed, the media's creation time is used
         # instead. Both thumbnails and the original media will be removed.
         #
         # Media is 'accessed' when loaded in a room in a client, or
         # otherwise downloaded by a local or remote user.
         #
+        # Purging the media will be the carried out by the media worker
+        # (whichever worker has the 'enable_media_repo' homeserver config
+        # option enabled). This may be the main process.
+        #
         media_retention:
             # Whether media retention settings should apply. Defaults to
             # false.