fix(emqx_retainer): remove disc_only option

apps/emqx_retainer/README.md

@@ -13,10 +13,9 @@ etc/emqx_retainer.conf:
 ## Where to store the retained messages.
 ## Notice that all nodes in a cluster are to have the same storage_type.
 ##
-## Value: ram | disc | disc_only
+## Value: ram | disc
 ##  - ram: memory only
 ##  - disc: both memory and disc
-##  - disc_only: disc only
 ##
 ## Default: ram
 retainer.storage_type = ram
@@ -56,4 +55,3 @@ Author
 ------
 
 EMQ X Team
-

apps/emqx_retainer/etc/emqx_retainer.conf

@@ -74,7 +74,7 @@ emqx_retainer {
 
     type = built_in_database
 
-    ## storage_type: ram | disc | disc_only
+    ## storage_type: ram | disc
     storage_type = ram
 
     ## Maximum number of retained messages. 0 means no limit.

apps/emqx_retainer/src/emqx_retainer_mnesia.erl

@@ -45,24 +45,22 @@
 create_resource(#{storage_type := StorageType}) ->
     Copies = case StorageType of
                  ram       -> ram_copies;
-                 disc      -> disc_copies;
-                 disc_only -> disc_only_copies
-             end,
-    TableType = case StorageType of
-                    disc_only -> set;
-                    _ -> ordered_set
+                 disc      -> disc_copies
              end,
+
     StoreProps = [{ets, [compressed,
                          {read_concurrency, true},
                          {write_concurrency, true}]},
                   {dets, [{auto_save, 1000}]}],
+
     ok = mria:create_table(?TAB, [
-                {type, TableType},
+                                  {type, ordered_set},
                                   {rlog_shard, ?RETAINER_SHARD},
                                   {storage, Copies},
                                   {record_name, retained},
                                   {attributes, record_info(fields, retained)},
-                {storage_properties, StoreProps}]),
+                                  {storage_properties, StoreProps}
+                                 ]),
     ok = mria_rlog:wait_for_shards([?RETAINER_SHARD], infinity),
     case mnesia:table_info(?TAB, storage_type) of
         Copies -> ok;

apps/emqx_retainer/src/emqx_retainer_schema.erl

@@ -20,7 +20,7 @@ fields("emqx_retainer") ->
 
 fields(mnesia_config) ->
     [ {type, ?TYPE(hoconsc:union([built_in_database]))}
-    , {storage_type, sc(hoconsc:union([ram, disc, disc_only]), ram)}
+    , {storage_type, sc(hoconsc:union([ram, disc]), ram)}
     , {max_retained_messages, sc(integer(), 0, fun is_pos_integer/1)}
     ];