feat(persistent_sessions): make table type in mnesia backend configurable

apps/emqx/etc/emqx.conf

@@ -1646,6 +1646,12 @@ persistent_session_store {
     ## ValueType: Boolean
     ## Default: false
     enabled = false
+    ## Which database backend should be used
+    ##
+    ## @doc persistent_session_store.db_backend
+    ## ValueType: mnesia_ram | mnesia_disc
+    ## Default: mnesia_ram
+    db_backend = mnesia_ram
 
     ## How long are undelivered messages retained in the store
     ##

apps/emqx/src/emqx_persistent_session.erl

@@ -82,12 +82,17 @@
 init_db_backend() ->
     case is_store_enabled() of
         true  ->
-            ok = emqx_trie:create_session_trie(),
-            emqx_persistent_session_mnesia_backend:create_tables(),
-            persistent_term:put(?db_backend_key, emqx_persistent_session_mnesia_backend),
+            TableType =
+                case emqx_config:get(?db_backend_key) of
+                    mnesia_ram -> ram_copies;
+                    mnesia_disc -> disc_copies
+                end,
+            ok = emqx_trie:create_session_trie(TableType),
+            emqx_persistent_session_mnesia_backend:create_tables(TableType),
+            persistent_term:put(?db_backend_module, emqx_persistent_session_mnesia_backend),
             ok;
         false ->
-            persistent_term:put(?db_backend_key, emqx_persistent_session_dummy_backend),
+            persistent_term:put(?db_backend_module, emqx_persistent_session_dummy_backend),
             ok
     end.
 

apps/emqx/src/emqx_persistent_session.hrl

@@ -30,4 +30,5 @@
 -define(is_enabled_key, [persistent_session_store, enabled]).
 -define(msg_retain, [persistent_session_store, max_retain_undelivered]).
 
--define(db_backend, (persistent_term:get(?db_backend_key))).
+-define(db_backend_module, [persistent_session_store, db_backend_module]).
+-define(db_backend, (persistent_term:get(?db_backend_module))).

apps/emqx/src/emqx_persistent_session_mnesia_backend.erl

@@ -19,7 +19,7 @@
 -include("emqx.hrl").
 -include("emqx_persistent_session.hrl").
 
--export([ create_tables/0
+-export([ create_tables/1
         , first_message_id/0
         , next_message_id/1
         , delete_message/1
@@ -35,11 +35,12 @@
         , ro_transaction/1
         ]).
 
-create_tables() ->
+create_tables(TableType) when TableType =:= ram_copies;
+                              TableType =:= disc_copies ->
     ok = mria:create_table(?SESSION_STORE, [
                 {type, set},
                 {rlog_shard, ?PERSISTENT_SESSION_SHARD},
-                {storage, disc_copies},
+                {storage, TableType},
                 {record_name, session_store},
                 {attributes, record_info(fields, session_store)},
                 {storage_properties, [{ets, [{read_concurrency, true}]}]}]),
@@ -47,7 +48,7 @@ create_tables() ->
     ok = mria:create_table(?SESS_MSG_TAB, [
                 {type, ordered_set},
                 {rlog_shard, ?PERSISTENT_SESSION_SHARD},
-                {storage, disc_copies},
+                {storage, TableType},
                 {record_name, session_msg},
                 {attributes, record_info(fields, session_msg)},
                 {storage_properties, [{ets, [{read_concurrency, true},
@@ -56,7 +57,7 @@ create_tables() ->
     ok = mria:create_table(?MSG_TAB, [
                 {type, ordered_set},
                 {rlog_shard, ?PERSISTENT_SESSION_SHARD},
-                {storage, disc_copies},
+                {storage, TableType},
                 {record_name, message},
                 {attributes, record_info(fields, message)},
                 {storage_properties, [{ets, [{read_concurrency, true},

apps/emqx/src/emqx_schema.erl

@@ -160,6 +160,10 @@ fields("persistent_session_store") ->
        sc(boolean(),
           #{ default => "false"
            })},
+      {"db_backend",
+       sc(hoconsc:union([mnesia_ram, mnesia_disc]),
+          #{ default => "mnesia_ram"
+           })},
       {"max_retain_undelivered",
        sc(duration(),
           #{ default => "1h"

apps/emqx/src/emqx_trie.erl

@@ -20,7 +20,7 @@
 
 %% Mnesia bootstrap
 -export([ mnesia/1
-        , create_session_trie/0
+        , create_session_trie/1
         ]).
 
 -boot_mnesia({mnesia, [boot]}).
@@ -75,13 +75,14 @@ mnesia(boot) ->
                 {type, ordered_set},
                 {storage_properties, StoreProps}]).
 
-create_session_trie() ->
+create_session_trie(TableType) when TableType =:= ram_copies;
+                                    TableType =:= disc_copies ->
     StoreProps = [{ets, [{read_concurrency, true},
                          {write_concurrency, true}
                         ]}],
     ok = mria:create_table(?SESSION_TRIE,
                            [{rlog_shard, ?ROUTE_SHARD},
-                            {storage, disc_copies},
+                            {storage, TableType},
                             {record_name, ?TRIE},
                             {attributes, record_info(fields, ?TRIE)},
                             {type, ordered_set},