From 79ce4791a326b15bec80e1a3870136548419a212 Mon Sep 17 00:00:00 2001
From: James Wheare <james@wheare.org>
Date: Tue, 25 Sep 2012 15:23:55 +0100
Subject: mnesia: Use chained send_after instead of send_interval

timer:send_interval behaves badly when resuming from sleep on some
platforms. For example, if I sleep for 10 minutes, and have a
send_interval running once per minute, when I resume, 10 messages
will be sent immediately, eliminating the benefit of only running
the work periodically. This is admittedly a separate bug with
send_interval, but the workaround is straightforward, and also
protects from messages piling up in the queue when the work takes
longer than the interval.

This patch fixes piled up error reports on resume from sleep:

** WARNING ** Mnesia is overloaded: {dump_log, write_threshold}

You'll still be warned if mnesia is overloaded, just not repeatedly.

Additionally, erlang:send_after is more efficient than using the
timer module equivalent [1]

[1] http://www.erlang.org/doc/efficiency_guide/commoncaveats.html#id57251
---
 lib/mnesia/src/mnesia_recover.erl | 66 ++++++++++++++++++++++-----------------
 1 file changed, 37 insertions(+), 29 deletions(-)

(limited to 'lib/mnesia/src/mnesia_recover.erl')

diff --git a/lib/mnesia/src/mnesia_recover.erl b/lib/mnesia/src/mnesia_recover.erl
index 4750291a10..b64f428f15 100644
--- a/lib/mnesia/src/mnesia_recover.erl
+++ b/lib/mnesia/src/mnesia_recover.erl
@@ -45,7 +45,8 @@
 	 note_log_decision/2,
 	 outcome/2,
 	 start/0,
-	 start_garb/0,
+	 next_garb/0,
+	 next_check_overload/0,
 	 still_pending/1,
 	 sync_trans_tid_serial/1,
 	 sync/0,
@@ -91,10 +92,38 @@ start() ->
 init() ->
     call(init).
 
-start_garb() ->
+next_garb() ->
     Pid = whereis(mnesia_recover),
-    {ok, _} = timer:send_interval(timer:minutes(2), Pid, garb_decisions),
-    {ok, _} = timer:send_interval(timer:seconds(10), Pid, check_overload).
+    erlang:send_after(timer:minutes(2), Pid, garb_decisions).
+
+next_check_overload() ->
+    Pid = whereis(mnesia_recover),
+    erlang:send_after(timer:seconds(10), Pid, check_overload).
+
+
+do_check_overload(S) ->
+    %% Time to check if mnesia_tm is overloaded
+    case whereis(mnesia_tm) of
+    Pid when is_pid(Pid) ->
+        Threshold = 100,
+        Prev = S#state.tm_queue_len,
+        {message_queue_len, Len} =
+        process_info(Pid, message_queue_len),
+        if
+        Len > Threshold, Prev > Threshold ->
+            What = {mnesia_tm, message_queue_len, [Prev, Len]},
+            mnesia_lib:report_system_event({mnesia_overload, What}),
+            mnesia_lib:overload_set(mnesia_tm, true),
+            S#state{tm_queue_len = 0};
+        Len > Threshold ->
+            S#state{tm_queue_len = Len};
+        true ->
+            mnesia_lib:overload_set(mnesia_tm, false),
+            S#state{tm_queue_len = 0}
+        end;
+    undefined ->
+        S
+    end.
 
 allow_garb() ->
     cast(allow_garb).
@@ -853,34 +882,13 @@ handle_info({connect_nodes, Ns, From}, State) ->
     handle_call({connect_nodes,Ns},From,State);
 
 handle_info(check_overload, S) ->
-    %% Time to check if mnesia_tm is overloaded
-    case whereis(mnesia_tm) of
-	Pid when is_pid(Pid) ->
-	    
-	    Threshold = 100,
-	    Prev = S#state.tm_queue_len,
-	    {message_queue_len, Len} =
-		process_info(Pid, message_queue_len),
-	    if
-		Len > Threshold, Prev > Threshold ->
-		    What = {mnesia_tm, message_queue_len, [Prev, Len]},
-		    mnesia_lib:report_system_event({mnesia_overload, What}),
-                    mnesia_lib:overload_set(mnesia_tm, true),
-		    {noreply, S#state{tm_queue_len = 0}};
-		
-		Len > Threshold ->
-		    {noreply, S#state{tm_queue_len = Len}};
-		
-		true ->
-                    mnesia_lib:overload_set(mnesia_tm, false),
-		    {noreply, S#state{tm_queue_len = 0}}
-	    end;
-	undefined ->
-	    {noreply, S}
-    end;
+    State2 = do_check_overload(S),
+    next_check_overload(),
+    {noreply, State2};
 
 handle_info(garb_decisions, State) ->
     do_garb_decisions(),
+    next_garb(),
     {noreply, State};
 
 handle_info({force_decision, Tid}, State) ->
-- 
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