Add message-poll-limit ...

server/server.yml

@@ -327,6 +327,15 @@
 # - message-delay-limit defines the max delay of a message when using the "Delay" header.
 #
 # message-size-limit: "4k"
+
+# Max number of cached messages returned per topic when the cache is replayed, i.e. a poll or a
+# "since" request. A poll without a "since" cursor returns a topic's entire cache, which is
+# unbounded in size. Uncapped by default, to preserve the historical behavior; set it to bound
+# how large a single replay can get. The newest messages are kept, and a truncated response
+# carries an "X-Messages-Truncated: 1" header. Together with message-size-limit this bounds the
+# memory one replay can allocate: limit x message-size-limit (e.g. 5000 x 4096 = ~20 MB).
+#
+# message-poll-limit: 5000
 # message-delay-limit: "3d"
 
 # Rate limiting: Total number of topics before the server rejects new topics.