From a318532bb04abf014b2e668f273c529675c84579 Mon Sep 17 00:00:00 2001
From: Feng Lee <feng@emqx.io>
Date: Fri, 17 Jan 2020 09:42:16 +0800
Subject: [PATCH] Tuning the 'force_gc_policy' of MQTT connections (#3192)

Tuning the 'force_gc_policy' of MQTT connections
---
 etc/emqx.conf              | 7 +++++--
 priv/emqx.schema           | 1 -
 src/emqx_misc.erl          | 3 +--
 src/emqx_ws_connection.erl | 4 ++--
 src/emqx_zone.erl          | 4 +++-
 5 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/etc/emqx.conf b/etc/emqx.conf
index 0c4ea81a5..b331fefd7 100644
--- a/etc/emqx.conf
+++ b/etc/emqx.conf
@@ -601,11 +601,11 @@ zone.external.enable_stats = on
 ## Default: ignore
 zone.external.acl_deny_action = ignore
 
-## Force MQTT connection/session process GC after this number of
+## Force the MQTT connection process GC after this number of
 ## messages | bytes passed through.
 ##
 ## Numbers delimited by `|'. Zero or negative is to disable.
-zone.external.force_gc_policy = 1000|1MB
+zone.external.force_gc_policy = 10000|10MB
 
 ## Max message queue length and total heap size to force shutdown
 ## connection/session process.
@@ -792,6 +792,9 @@ zone.internal.enable_acl = off
 ## Default: ignore
 zone.internal.acl_deny_action = ignore
 
+## See zone.$name.force_gc_policy
+## zone.internal.force_gc_policy = 100000|100MB
+
 ## See zone.$name.wildcard_subscription.
 ##
 ## Value: boolean
diff --git a/priv/emqx.schema b/priv/emqx.schema
index a6966f0a5..662415a68 100644
--- a/priv/emqx.schema
+++ b/priv/emqx.schema
@@ -915,7 +915,6 @@ end}.
 %% messages | bytes passed through.
 %% Numbers delimited by `|'. Zero or negative is to disable.
 {mapping, "zone.$name.force_gc_policy", "emqx.zones", [
-   {default, "0 | 0MB"},
    {datatype, string}
  ]}.
 
diff --git a/src/emqx_misc.erl b/src/emqx_misc.erl
index f5fe5029f..d08d3ba35 100644
--- a/src/emqx_misc.erl
+++ b/src/emqx_misc.erl
@@ -58,8 +58,7 @@ merge_opts(Defaults, Options) ->
 %% @doc Apply a function to a maybe argument.
 -spec(maybe_apply(fun((maybe(A)) -> maybe(A)), maybe(A))
       -> maybe(A) when A :: any()).
-maybe_apply(_Fun, undefined) ->
-    undefined;
+maybe_apply(_Fun, undefined) -> undefined;
 maybe_apply(Fun, Arg) when is_function(Fun) ->
     erlang:apply(Fun, [Arg]).
 
diff --git a/src/emqx_ws_connection.erl b/src/emqx_ws_connection.erl
index ceae32823..204dc82ee 100644
--- a/src/emqx_ws_connection.erl
+++ b/src/emqx_ws_connection.erl
@@ -429,9 +429,9 @@ ensure_rate_limit(Stats, State = #state{limiter = Limiter}) ->
 
 run_gc(Stats, State = #state{gc_state = GcSt}) ->
     case ?ENABLED(GcSt) andalso emqx_gc:run(Stats, GcSt) of
+        false -> State;
         {_IsGC, GcSt1} ->
-            State#state{gc_state = GcSt1};
-        false -> State
+            State#state{gc_state = GcSt1}
     end.
 
 check_oom(State = #state{channel = Channel}) ->
diff --git a/src/emqx_zone.erl b/src/emqx_zone.erl
index 0304f4c8a..68befdfdc 100644
--- a/src/emqx_zone.erl
+++ b/src/emqx_zone.erl
@@ -45,6 +45,8 @@
           , session_expiry_interval/1
           , force_gc_policy/1
           , force_shutdown_policy/1
+          , get_env/2
+          , get_env/3
           ]}).
 
 %% APIs
@@ -114,7 +116,7 @@ start_link() ->
 stop() ->
     gen_server:stop(?SERVER).
 
--spec(init_gc_state(zone()) -> emqx_gc:gc_state()).
+-spec(init_gc_state(zone()) -> maybe(emqx_gc:gc_state())).
 init_gc_state(Zone) ->
     maybe_apply(fun emqx_gc:init/1, force_gc_policy(Zone)).