From 657df05ad9d762fb6e4bf3c2758d02b31c7ae3cc Mon Sep 17 00:00:00 2001
From: Thales Macedo Garitezi <thalesmg@gmail.com>
Date: Tue, 16 May 2023 09:45:54 -0300
Subject: [PATCH] fix(buffer_worker): avoid setting flush timer when inflight
 is full
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Fixes https://emqx.atlassian.net/browse/EMQX-9902

When the buffer worker inflight window is full, we don’t need to set a
timer to flush the messages again because there’s no more room, and
one of the inflight windows will flush the buffer worker by calling
`flush_worker`.

Currently, we do set the timer on such situation, and this fact
combined with the default batch time of 0 yields a busy loop situation
where the CPU spins a lot while inflight messages do not return.
---
 apps/emqx_resource/src/emqx_resource.app.src           | 2 +-
 apps/emqx_resource/src/emqx_resource_buffer_worker.erl | 3 +--
 changes/ce/fix-10717.en.md                             | 1 +
 3 files changed, 3 insertions(+), 3 deletions(-)
 create mode 100644 changes/ce/fix-10717.en.md

diff --git a/apps/emqx_resource/src/emqx_resource.app.src b/apps/emqx_resource/src/emqx_resource.app.src
index 3e264cb3e..3b92f1200 100644
--- a/apps/emqx_resource/src/emqx_resource.app.src
+++ b/apps/emqx_resource/src/emqx_resource.app.src
@@ -1,7 +1,7 @@
 %% -*- mode: erlang -*-
 {application, emqx_resource, [
     {description, "Manager for all external resources"},
-    {vsn, "0.1.15"},
+    {vsn, "0.1.16"},
     {registered, []},
     {mod, {emqx_resource_app, []}},
     {applications, [
diff --git a/apps/emqx_resource/src/emqx_resource_buffer_worker.erl b/apps/emqx_resource/src/emqx_resource_buffer_worker.erl
index 2dd14c46b..8c5311f2a 100644
--- a/apps/emqx_resource/src/emqx_resource_buffer_worker.erl
+++ b/apps/emqx_resource/src/emqx_resource_buffer_worker.erl
@@ -495,8 +495,7 @@ flush(Data0) ->
             {keep_state, Data1};
         {_, true} ->
             ?tp(buffer_worker_flush_but_inflight_full, #{}),
-            Data2 = ensure_flush_timer(Data1),
-            {keep_state, Data2};
+            {keep_state, Data1};
         {_, false} ->
             ?tp(buffer_worker_flush_before_pop, #{}),
             {Q1, QAckRef, Batch} = replayq:pop(Q0, #{count_limit => BatchSize}),
diff --git a/changes/ce/fix-10717.en.md b/changes/ce/fix-10717.en.md
new file mode 100644
index 000000000..4c33d6971
--- /dev/null
+++ b/changes/ce/fix-10717.en.md
@@ -0,0 +1 @@
+Fixed an issue where the buffering layer processes could use a lot of CPU when inflight window is full.