Addressing Mnesia backend failing on erldns_zone_cache functions (#103)

* Addressing Mnesia backend failing on erldns_zone_cache functions:

* added type bag on table creation (zone_records, zone_records_typed)
* set explicit type set on table creation (zones)
* refactored select/3: using ETS match spec converted to Mnesia's
match_object pattern

* Mnesia related changes:

* using different pattern in erldns_zone_cache:zone_names_and_versions/0
depending on backend (ETS/Mnesia foldl/3 return values are different)
* debug artefacts cleanup

* * refactored erldns_zone_cache:get_records_by_name to call
erldns_storage:select/3 vs select/2
* added flattening returned from the select/3

Author: m0rcq

src/erldns_storage.erl

@@ -43,7 +43,6 @@
          terminate/2,
          code_change/3]).
 
-
 -record(state, {}).
 
 -define(POLL_WAIT_HOURS, 1).

src/erldns_storage_mnesia.erl

@@ -72,6 +72,7 @@ create(zones) ->
   case mnesia:create_table(zones,
                            [{attributes, record_info(fields, zone)},
                             {record_name, zone},
+			    {type, set},
                             {disc_copies, [node()]}]) of
     {aborted, {already_exists, zones}} ->
       lager:warning("The zone table already exists (node: ~p)", [node()]),
@@ -84,7 +85,9 @@ create(zones) ->
 create(zone_records) ->
   case mnesia:create_table(zone_records,
                            [{attributes, record_info(fields, zone_records)},
-                            {disc_copies, [node()]}]) of
+                            {disc_copies, [node()]},
+			    {type, bag}
+			   ]) of
     {aborted, {already_exists, zone_records}} ->
       lager:warning("The zone records table already exists (node: ~p)", [node()]),
       ok;
@@ -96,9 +99,11 @@ create(zone_records) ->
 create(zone_records_typed) ->
   case mnesia:create_table(zone_records_typed,
                            [{attributes, record_info(fields, zone_records_typed)},
-                            {disc_copies, [node()]}]) of
+                            {disc_copies, [node()]},
+			    {type, bag}
+			   ]) of
     {aborted, {already_exists, zone_records_typed}} ->
-      lager:warning("The zone records table already exists (node: ~p)", [node()]),
+      lager:warning("The zone records typed table already exists (node: ~p)", [node()]),
       ok;
     {atomic, ok} ->
       ok;
@@ -192,7 +197,7 @@ delete(Table, Key)->
 -spec select_delete(atom(), list()) -> {ok, Count :: integer()} | {error, Reason :: term()}.
 select_delete(Table, [{{{ZoneName, Fqdn}, _}, _, _}])->
   SelectDelete = fun() ->
-                     Records =  mnesia:match_object(Table, {zone_records, ZoneName, Fqdn, '_'}, write),
+                     Records =  mnesia:match_object(Table, {zone_records, ZoneName, Fqdn, '_'}, read),
                      lists:foreach(fun(R) -> mnesia:dirty_delete_object(R) end, Records),
                      {ok, length(Records)}
                  end,
@@ -229,11 +234,20 @@ select(Table, Key)->
            end,
   mnesia:activity(transaction, Select).
 
-%% @doc Select using a match spec.
+%% @doc Select using ETS match spec converted to Mnesia's match_object pattern
 -spec select(atom(), list(), infinite | integer()) -> [tuple()].
-select(_Table, MatchSpec, _Limit) ->
-  MatchObject = fun() -> mnesia:match_object(MatchSpec) end,
-  mnesia:activity(transaction, MatchObject).
+select(Table, [{{{ZoneName, Fqdn}, _}, _, _}], _Limit) ->
+  SelectFun = fun() ->
+    Records  = mnesia:match_object(Table, {zone_records, ZoneName, Fqdn, '_'}, read),
+    [Record || {_, _, _, Record} <- Records] 
+  end,
+  mnesia:activity(transaction, SelectFun);
+select(Table, [{{{ZoneName, Fqdn, Type}, _}, _, _}], _Limit) ->
+  SelectFun = fun() ->
+     Records = mnesia:match_object(Table, {zone_records_typed, ZoneName, Fqdn, Type, '_'}, read),
+     [Record || {_, _, _, _, Record} <- Records] 
+  end,
+  mnesia:activity(transaction, SelectFun).
 
 %% @doc Wrapper for foldl.
 -spec foldl(fun(), list(), atom())  -> Acc :: term() | {error, Reason :: term()}.

src/erldns_zone_cache.erl

@@ -170,10 +170,7 @@ get_records_by_name_and_type(Name, Type) ->
 get_records_by_name(Name) ->
   case find_zone_in_cache(Name) of
     {ok, Zone} ->
-      case erldns_storage:select(zone_records, {erldns:normalize_name(Zone#zone.name), erldns:normalize_name(Name)}) of
-        [] -> [];
-        [{_, Records}] -> Records
-      end; 
+      lists:flatten(erldns_storage:select(zone_records,[{{{erldns:normalize_name(Zone#zone.name), erldns:normalize_name(Name)}, '$1'},[],['$$']}], infinite));
     _ ->
       []
   end.
@@ -192,7 +189,13 @@ in_zone(Name) ->
 %% for the zone.
 -spec zone_names_and_versions() -> [{dns:dname(), binary()}].
 zone_names_and_versions() ->
-  erldns_storage:foldl(fun({_, Zone}, NamesAndShas) -> NamesAndShas ++ [{Zone#zone.name, Zone#zone.version}] end, [], zones).
+  % ETS and Mnesia foldl/3 differ in return values -> Mnesia's version is missing key
+  case erldns_config:storage_type() of 
+    erldns_storage_json -> 
+	erldns_storage:foldl(fun({_, Zone}, NamesAndShas) -> NamesAndShas ++ [{Zone#zone.name, Zone#zone.version}] end, [], zones);
+    erldns_storage_mnesia ->
+	erldns_storage:foldl(fun(Zone, NamesAndShas) -> NamesAndShas ++ [{Zone#zone.name, Zone#zone.version}] end, [], zones)
+  end.
 
 % ----------------------------------------------------------------------------------------------------
 % Write API