perf: reduce the mem used when get_pool_by_slot

src/eredis_cluster_monitor.erl

@@ -4,7 +4,7 @@
 %% API.
 -export([start_link/2]).
 -export([refresh_mapping/2]).
--export([get_state/1, get_state_version/1]).
+-export([get_state/1, cache_states/0, get_state_version/1]).
 -export([get_pool_by_slot/2]).
 -export([get_all_pools/1]).
 -export([get_slot_samples/1]).
@@ -33,6 +33,8 @@
     pool_options = [] :: list(tuple())
 }).
 
+-define(PK, ?MODULE).
+
 %% API.
 start_link(Name, Opts) ->
     gen_server:start_link(?MODULE, [Name, Opts], []).
@@ -43,15 +45,38 @@ refresh_mapping(Name, Version) ->
         Pid -> gen_server:call(Pid, {reload_slots_map, Version})
     end.
 
+get_config() ->
+    persistent_term:get(?PK, #{}).
+
+get_config(Key, Default) ->
+    maps:get(Key, get_config(), Default).
+
+set_config(Key, Value) ->
+    persistent_term:put(?PK, maps:put(Key, Value, get_config())).
+
 %% =============================================================================
 %% @doc Given a slot return the link (Redis instance) to the mapped
 %% node.
 %% @end
 %% =============================================================================
+set_state(Name, State) ->
+    set_config(state, maps:put(Name, State, get_config(state, #{}))).
+
 get_state(Name) ->
-    case ets:lookup(?MODULE, Name) of
-        [] -> #state{};
-        [{Name, State}] -> State
+    case maps:find(Name, get_config(state, #{})) of
+        {ok, State} -> State;
+        error -> throw({?MODULE, {state_not_initialized, Name}})
+    end.
+
+%% The older version of get_state/1 stored the state in ets, we read and cache
+%% it in the persistent term
+cache_states() ->
+    case ets:info(?MODULE) of
+        undefined -> ok;
+        _ ->
+            lists:foreach(fun({Name, State}) ->
+                    set_state(Name, State)
+                end, ets:tab2list(?MODULE))
     end.
 
 get_state_version(State) ->
@@ -79,8 +104,7 @@ get_pool_by_slot(Slot, State) when is_integer(Slot) ->
     end;
 
 get_pool_by_slot(Name, Slot) ->
-    State = get_state(Name),
-    get_pool_by_slot(Slot, State).
+    get_pool_by_slot(Slot, get_state(Name)).
 
 get_slot_samples(Name) ->
     #state{slots_maps = SlotsMaps0} = get_state(Name),
@@ -108,7 +132,7 @@ reload_slots_map(State = #state{pool_name = PoolName}) ->
                 version = State#state.version + 1
             }
     end,
-    true = ets:insert(?MODULE, [{PoolName, NewState}]),
+    set_state(PoolName, NewState),
     NewState.
 
 get_cluster_slots([], State, FailAcc) ->

test/eredis_cluster_tests.erl

@@ -206,7 +206,7 @@ basic_test_cases(AuthMethod) ->
         { "eredis_cluster_monitor:get_state" ++ AuthMethodSuffix,
         fun () ->
             ?assert(is_tuple(eredis_cluster_monitor:get_state(?POOL))),
-            ?assert(is_tuple(eredis_cluster_monitor:get_state(invalid_pool)))
+            ?assertThrow({_, {state_not_initialized, invalid_pool}}, eredis_cluster_monitor:get_state(invalid_pool))
         end
         },
 
@@ -219,7 +219,7 @@ basic_test_cases(AuthMethod) ->
         { "ping_all" ++ AuthMethodSuffix,
         fun () ->
             ?assert(eredis_cluster:ping_all(?POOL)),
-            ?assertNot(eredis_cluster:ping_all(invalid_pool))
+            ?assertThrow({_, {state_not_initialized, invalid_pool}}, eredis_cluster:ping_all(invalid_pool))
         end
         }
   ].