From f5c4fb5860130ad4cbfe47a43c165d558fa4bee7 Mon Sep 17 00:00:00 2001
From: Thales Macedo Garitezi <thalesmg@gmail.com>
Date: Tue, 28 Nov 2023 09:58:03 -0300
Subject: [PATCH] fix(ds_session): take conservative estimate of
 `last_alive_at` when bumping

Addresses https://github.com/emqx/emqx/pull/12024#discussion_r1407432154
---
 apps/emqx/src/emqx_persistent_session_ds.erl | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/apps/emqx/src/emqx_persistent_session_ds.erl b/apps/emqx/src/emqx_persistent_session_ds.erl
index 97825e728..f66d9d451 100644
--- a/apps/emqx/src/emqx_persistent_session_ds.erl
+++ b/apps/emqx/src/emqx_persistent_session_ds.erl
@@ -399,8 +399,13 @@ handle_timeout(_ClientInfo, get_streams, Session) ->
     ensure_timer(get_streams),
     {ok, [], Session};
 handle_timeout(_ClientInfo, bump_last_alive_at, Session0) ->
-    NowMS = now_ms(),
-    Session = session_set_last_alive_at_trans(Session0, NowMS),
+    %% Note: we take a pessimistic approach here and assume that the client will be alive
+    %% until the next bump timeout.  With this, we avoid garbage collecting this session
+    %% too early in case the session/connection/node crashes earlier without having time
+    %% to commit the time.
+    BumpInterval = emqx_config:get([session_persistence, last_alive_update_interval]),
+    EstimatedLastAliveAt = now_ms() + BumpInterval,
+    Session = session_set_last_alive_at_trans(Session0, EstimatedLastAliveAt),
     ensure_timer(bump_last_alive_at),
     {ok, [], Session}.