File 3431-Optimise-mnesia-table-loading-time-for-busy-tables.patch of Package erlang

From 455085809cb5de2570bbba7da8b607c38939e83c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Smyczy=C5=84ski?= <s.smyczynski@simplito.com>
Date: Thu, 4 Mar 2021 00:28:59 +0100
Subject: [PATCH] Optimise mnesia table loading time for busy tables

---
 lib/mnesia/src/mnesia_loader.erl | 52 +++++++++++++++++++++++++-------
 1 file changed, 41 insertions(+), 11 deletions(-)

diff --git a/lib/mnesia/src/mnesia_loader.erl b/lib/mnesia/src/mnesia_loader.erl
index c34a83bb6c..a2fde5c808 100644
--- a/lib/mnesia/src/mnesia_loader.erl
+++ b/lib/mnesia/src/mnesia_loader.erl
@@ -320,6 +320,11 @@ start_remote_sender(Node,Tab,Storage) ->
 
 table_init_fun(SenderPid, Storage) ->
     fun(read) ->
+	    % We want to store subscribed mnesia table events received during
+	    % table copying for later processing to not let receiver message queue
+	    % to grow too much (which in consequence would slow down the whole copying process)
+	    SubscrCache = ets:new(subscr_cache, [private, ordered_set]),
+	    put(mnesia_table_receiver_subscr_cache, SubscrCache),
 	    Receiver = self(),
 	    SenderPid ! {Receiver, more},
 	    get_data(SenderPid, Receiver, Storage);
@@ -471,6 +476,10 @@ get_data(Pid, TabRec, Storage) ->
 	    end;
 	{'EXIT', Pid, Reason} ->
 	    handle_exit(Pid, Reason),
+	    get_data(Pid, TabRec, Storage);
+	{mnesia_table_event, _} = SubscrEvent ->
+	    SubscrCache = get(mnesia_table_receiver_subscr_cache),
+	    ets:insert(SubscrCache, {erlang:unique_integer([monotonic]), SubscrEvent}),
 	    get_data(Pid, TabRec, Storage)
     end.
 
@@ -542,7 +551,7 @@ init_table(Tab, _, Fun, _DetsInfo,_) ->
 
 finish_copy(Storage,Tab,Cs,SenderPid,DatBin,OrigTabRec) ->
     TabRef = {Storage, Tab},
-    subscr_receiver(TabRef, Cs#cstruct.record_name),
+    subscr_postprocess(TabRef, Cs#cstruct.record_name),
     case handle_last(TabRef, Cs#cstruct.type, DatBin) of
 	ok ->
 	    mnesia_index:init_index(Tab, Storage),
@@ -558,8 +567,37 @@ finish_copy(Storage,Tab,Cs,SenderPid,DatBin,OrigTabRec) ->
 	    down(Tab, Storage)
     end.
 
+subscr_postprocess(TabRef, RecName) ->
+    % process events received during table copying
+    case get(mnesia_table_receiver_subscr_cache) of
+	undefined ->
+	    ok;
+	SubscrCache ->
+	    ets:foldl(
+		fun({_, Event}, _Acc) ->
+		    handle_subscr_event(Event, TabRef, RecName)
+		end, ok, SubscrCache),
+	    ets:delete(SubscrCache)
+    end,
+    % and all remaining events
+    subscr_receiver(TabRef, RecName).
+
 subscr_receiver(TabRef = {_, Tab}, RecName) ->
     receive
+	{mnesia_table_event, {_Op, Val, _Tid}} = Event
+	  when element(1, Val) =:= Tab; element(1, Val) =:= schema ->
+	    handle_subscr_event(Event, TabRef, RecName),
+	    subscr_receiver(TabRef, RecName);
+
+	{'EXIT', Pid, Reason} ->
+	    handle_exit(Pid, Reason),
+	    subscr_receiver(TabRef, RecName)
+    after 0 ->
+	    ok
+    end.
+
+handle_subscr_event(Event, TabRef = {_, Tab}, RecName) ->
+    case Event of
 	{mnesia_table_event, {Op, Val, _Tid}}
 	  when element(1, Val) =:= Tab ->
 	    if
@@ -567,8 +605,7 @@ subscr_receiver(TabRef = {_, Tab}, RecName) ->
 		    handle_event(TabRef, Op, Val);
 		true ->
 		    handle_event(TabRef, Op, setelement(1, Val, RecName))
-	    end,
-	    subscr_receiver(TabRef, RecName);
+	    end;
 
 	{mnesia_table_event, {Op, Val, _Tid}} when element(1, Val) =:= schema ->
 	    %% clear_table is faked via two schema events
@@ -576,14 +613,7 @@ subscr_receiver(TabRef = {_, Tab}, RecName) ->
 	    case Op of
 		delete -> handle_event(TabRef, clear_table, {Tab, all});
 		_ -> ok
-	    end,
-	    subscr_receiver(TabRef, RecName);
-
-	{'EXIT', Pid, Reason} ->
-	    handle_exit(Pid, Reason),
-	    subscr_receiver(TabRef, RecName)
-    after 0 ->
-	    ok
+	    end
     end.
 
 handle_event(TabRef, write, Rec) ->
-- 
2.26.2