Make Mnesia DCD dump behaviour available via configuration

Setting the new Mnesia parameter 'dump_disc_copies_at_startup' to
'false' will completely disable the DCD dumping while tables are being
loaded. If it is set to 'true' (the default), the same test will now
be performed as for normal dumps, i.e., using the 'dc_dump_limit'
parameter. Previously, the test performed at load time was different
from the one used at runtime, and caused a lot of unnecessary dumping
which slowed down the startup.

4 files changed, 38 insertions, 23 deletions

diff --git a/lib/mnesia/doc/src/mnesia.xml b/lib/mnesia/doc/src/mnesia.xml
index 72e9bd7e8f..842f1641dd 100644
--- a/lib/mnesia/doc/src/mnesia.xml
+++ b/lib/mnesia/doc/src/mnesia.xml
@@ -3017,6 +3017,12 @@ raise(Name, Amount) ->
           totally unpredictable.</p>
       </item>
       <item>
+        <p><c>-mnesia dump_disc_copies_at_startup true | false</c>.
+          If set to false, this disables the dumping of <c>disc_copies</c>
+          tables during startup while tables are being loaded. The default
+          is true.</p>
+      </item>
+      <item>
         <p><c>-mnesia dump_log_load_regulation true | false</c>.
           Controls if the log dumps should be performed as fast as
           possible or if the dumper should do its own load
diff --git a/lib/mnesia/src/mnesia_dumper.erl b/lib/mnesia/src/mnesia_dumper.erl
index 14665797a0..b784f2aca3 100644
--- a/lib/mnesia/src/mnesia_dumper.erl
+++ b/lib/mnesia/src/mnesia_dumper.erl
@@ -34,6 +34,7 @@
 -export([
 	 get_log_writes/0,
 	 incr_log_writes/0,
+         needs_dump_ets/1,
 	 raw_dump_table/2,
 	 raw_named_dump_table/2,
 	 start_regulator/0,
@@ -981,28 +982,10 @@ open_files(_Tab, _Storage, _UpdateInPlace, _InitBy) ->
     false.
 
 open_disc_copies(Tab, InitBy) ->
-    DclF = mnesia_lib:tab2dcl(Tab),
-    DumpEts =
-	case file:read_file_info(DclF) of
-	    {error, enoent} ->
-		false;
-	    {ok, DclInfo} ->
-		DcdF =  mnesia_lib:tab2dcd(Tab),
-		case file:read_file_info(DcdF) of
-		    {error, Reason} ->
-			mnesia_lib:dbg_out("File ~p info_error ~p ~n",
-					   [DcdF, Reason]),
-			true;
-		    {ok, DcdInfo} ->
-			Mul = case ?catch_val(dc_dump_limit) of
-				  {'EXIT', _} -> ?DumpToEtsMultiplier;
-				  Val -> Val
-			      end,
-			DcdInfo#file_info.size =< (DclInfo#file_info.size * Mul)
-		end
-	end,
+    DumpEts = needs_dump_ets(Tab),
     if
 	DumpEts == false; InitBy == startup ->
+            DclF = mnesia_lib:tab2dcl(Tab),
 	    mnesia_log:open_log({?MODULE,Tab},
 				mnesia_log:dcl_log_header(),
 				DclF,
@@ -1017,6 +1000,27 @@ open_disc_copies(Tab, InitBy) ->
 	    false
     end.
 
+needs_dump_ets(Tab) ->
+    DclF = mnesia_lib:tab2dcl(Tab),
+    case file:read_file_info(DclF) of
+        {error, enoent} ->
+            false;
+        {ok, DclInfo} ->
+            DcdF =  mnesia_lib:tab2dcd(Tab),
+            case file:read_file_info(DcdF) of
+                {error, Reason} ->
+                    mnesia_lib:dbg_out("File ~p info_error ~p ~n",
+                                       [DcdF, Reason]),
+                    true;
+                {ok, DcdInfo} ->
+                    Mul = case ?catch_val(dc_dump_limit) of
+                              {'EXIT', _} -> ?DumpToEtsMultiplier;
+                              Val -> Val
+                          end,
+                    DcdInfo#file_info.size =< (DclInfo#file_info.size * Mul)
+            end
+    end.
+
 %% Always opens the dcl file for writing overriding already_dumped
 %% mechanismen, used for schema transactions.
 open_dcl(Tab) ->
diff --git a/lib/mnesia/src/mnesia_loader.erl b/lib/mnesia/src/mnesia_loader.erl
index 4afbea1cc2..ebd68c226a 100644
--- a/lib/mnesia/src/mnesia_loader.erl
+++ b/lib/mnesia/src/mnesia_loader.erl
@@ -69,9 +69,10 @@ do_get_disc_copy2(Tab, Reason, Storage, Type) when Storage == disc_copies ->
 	    ignore;
 	_ ->
 	    mnesia_monitor:mktab(Tab, Args),
-	    Count = mnesia_log:dcd2ets(Tab, Repair),
-	    case ets:info(Tab, size) of
-		X when X < Count * 4 ->
+	    _Count = mnesia_log:dcd2ets(Tab, Repair),
+	    case mnesia_monitor:get_env(dump_disc_copies_at_startup)
+		andalso mnesia_dumper:needs_dump_ets(Tab) of
+		true ->
 		    ok = mnesia_log:ets2dcd(Tab);
 		_ ->
 		    ignore
diff --git a/lib/mnesia/src/mnesia_monitor.erl b/lib/mnesia/src/mnesia_monitor.erl
index 6fc1a394a6..a0e0e630ec 100644
--- a/lib/mnesia/src/mnesia_monitor.erl
+++ b/lib/mnesia/src/mnesia_monitor.erl
@@ -664,6 +664,7 @@ env() ->
      backup_module,
      debug,
      dir,
+     dump_disc_copies_at_startup,
      dump_log_load_regulation,
      dump_log_time_threshold,
      dump_log_update_in_place,
@@ -692,6 +693,8 @@ default_env(debug) ->
 default_env(dir) ->
     Name = lists:concat(["Mnesia.", node()]),
     filename:absname(Name);
+default_env(dump_disc_copies_at_startup) ->
+    true;
 default_env(dump_log_load_regulation) ->
     false;
 default_env(dump_log_time_threshold) ->
@@ -741,6 +744,7 @@ do_check_type(debug, trace) -> trace;
 do_check_type(debug, true) -> debug;
 do_check_type(debug, verbose) -> verbose;
 do_check_type(dir, V) -> filename:absname(V);
+do_check_type(dump_disc_copies_at_startup, B) -> bool(B);
 do_check_type(dump_log_load_regulation, B) -> bool(B);
 do_check_type(dump_log_time_threshold, I) when is_integer(I), I > 0 -> I;
 do_check_type(dump_log_update_in_place, B) -> bool(B);