fix(mnesia): apply dump_log_write_threshold before mnesia start.

change_config rejected the key; set_env + verify enables the IFT ceiling ladder. Refs EventHub/EventHubBack#30 Refs EventHub/EventHubBack#34

Co-authored-by: Cursor <cursoragent@cursor.com>

src/config/sys.config

@@ -16,7 +16,10 @@
     ]}
   ]},
   {mnesia, [
-    {dir, "data/Mnesia.eventhub@${NODE_NAME}"}
+    {dir, "data/Mnesia.eventhub@${NODE_NAME}"},
+    %% Soften dump_log under write load; override via MNESIA_DUMP_LOG_WRITE_THRESHOLD
+    %% before start (infra_mnesia:configure_dump_log/0). OTP default ~1000.
+    {dump_log_write_threshold, 50000}
   ]},
   { cowboy_swagger, [
     { static_files, "./_build/default/lib/cowboy_swagger/priv/swagger" }

src/eventhub_app.erl

@@ -46,8 +46,9 @@ start_application() ->
           io:format("~nCluster: discovered nodes ~p, joining cluster~n", [Nodes]),
           application:set_env(eventhub, extra_db_nodes, Nodes)
       end,
-      application:ensure_all_started(mnesia),
       ok = infra_mnesia:configure_dump_log(),
+      application:ensure_all_started(mnesia),
+      ok = infra_mnesia:verify_dump_log(),
       ok = infra_mnesia:init_tables(),
       ok = infra_mnesia:wait_for_tables(),
       ok = migration_engine:ensure_applied(),

src/infra/infra_mnesia.erl

@@ -8,7 +8,7 @@
 
 -export([start_link/0, init_tables/0, wait_for_tables/0, wait_for_table/1]).
 -export([add_cluster_nodes/1]).
--export([configure_dump_log/0]).
+-export([configure_dump_log/0, verify_dump_log/0]).
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
   terminate/2, code_change/3]).
 
@@ -48,16 +48,31 @@ add_cluster_nodes(Nodes) ->
 %% @doc Soften dump_log overload under write-heavy load (IFT stress).
 %% OTP warns {dump_log, write_threshold|time_threshold} when a new dump
 %% is requested while the previous dump still runs.
+%% Must be set BEFORE mnesia starts — change_config/2 does not accept
+%% dump_log_write_threshold (returns {error, dump_log_write_threshold}).
 %% Override: MNESIA_DUMP_LOG_WRITE_THRESHOLD (default 50000; OTP default ~1000).
 -spec configure_dump_log() -> ok.
 configure_dump_log() ->
   Threshold = env_int("MNESIA_DUMP_LOG_WRITE_THRESHOLD", 50000),
-  case mnesia:change_config(dump_log_write_threshold, Threshold) of
-    {ok, Old} ->
-      io:format("Mnesia dump_log_write_threshold: ~p -> ~p~n", [Old, Threshold]),
+  case application:load(mnesia) of
+    ok -> ok;
+    {error, {already_loaded, mnesia}} -> ok;
+    {error, LoadErr} ->
+      io:format("Mnesia load before dump_log config failed: ~p~n", [LoadErr])
+  end,
+  ok = application:set_env(mnesia, dump_log_write_threshold, Threshold),
+  io:format("Mnesia dump_log_write_threshold set to ~p (before start)~n", [Threshold]),
+  ok.
+
+%% @doc Log active threshold after mnesia:start (sanity check for IFT logs).
+-spec verify_dump_log() -> ok.
+verify_dump_log() ->
+  case catch mnesia:system_info(dump_log_write_threshold) of
+    N when is_integer(N) ->
+      io:format("Mnesia dump_log_write_threshold active: ~p~n", [N]),
       ok;
     Other ->
-      io:format("Mnesia dump_log_write_threshold change failed: ~p~n", [Other]),
+      io:format("Mnesia dump_log_write_threshold verify: ~p~n", [Other]),
       ok
   end.