docs(ds): Add descriptions for the builtin's egress config

apps/emqx/src/emqx_ds_schema.erl

@@ -77,7 +77,7 @@ schema() ->
         {messages,
             ds_schema(#{
                 desc => ?DESC(messages),
-                importance => ?IMPORTANCE_HIDDEN,
+                importance => ?IMPORTANCE_MEDIUM,
                 default =>
                     #{
                         <<"backend">> => builtin
@@ -165,7 +165,8 @@ fields(builtin_egress) ->
                 #{
                     default => 1000,
                     mapping => "emqx_durable_storage.egress_batch_size",
-                    importance => ?IMPORTANCE_HIDDEN
+                    importance => ?IMPORTANCE_MEDIUM,
+                    desc => ?DESC(egress_max_items)
                 }
             )},
         {flush_interval,
@@ -174,7 +175,8 @@ fields(builtin_egress) ->
                 #{
                     default => 100,
                     mapping => "emqx_durable_storage.egress_flush_interval",
-                    importance => ?IMPORTANCE_HIDDEN
+                    importance => ?IMPORTANCE_MEDIUM,
+                    desc => ?DESC(egress_flush_interval)
                 }
             )}
     ];

apps/emqx/src/emqx_schema.erl

@@ -258,7 +258,7 @@ roots(medium) ->
         {"durable_storage",
             sc(
                 ref("durable_storage"),
-                #{importance => ?IMPORTANCE_HIDDEN}
+                #{importance => ?IMPORTANCE_MEDIUM}
             )}
     ];
 roots(low) ->

rel/i18n/emqx_ds_schema.hocon

@@ -47,4 +47,15 @@ wildcard_optimized_epoch_bits.desc:
   Each epoch can be consumed by the subscribers as a batch.
   Generally, larger epochs lead to higher throughput of subscribers, however currently they may increase latency.~"""
 
+egress_max_items.label: "Max items"
+egress_max_items.desc:
+  """~
+  This configuration parameter defines maximum number of buffered messages stored in the egress buffer.~"""
+
+egress_flush_interval.label: "Flush interval"
+egress_flush_interval.desc:
+  """~
+  Maximum linger time for the buffered messages.
+  Egress buffer will be flushed _at least_ as often as `flush_interval`.~"""
+
 }