fix(dsstore): avoid storing `cf_refs()` in the RocksDB itself

This is both pointless and confusing.

apps/emqx_durable_storage/src/emqx_ds_storage_layer.erl

@@ -111,7 +111,8 @@
 
 -type shard_id() :: {emqx_ds:db(), binary()}.
 
--type cf_refs() :: [{string(), rocksdb:cf_handle()}].
+-type cf_ref() :: {string(), rocksdb:cf_handle()}.
+-type cf_refs() :: [cf_ref()].
 
 -type gen_id() :: 0..16#ffff.
 
@@ -179,7 +180,7 @@
     %% Module-specific data defined at generation creation time:
     data := Data,
     %% Column families used by this generation
-    cf_refs := cf_refs(),
+    cf_names := [string()],
     %% Time at which this was created.  Might differ from `since', in particular for the
     %% first generation.
     created_at := emqx_message:timestamp(),
@@ -789,9 +790,9 @@ handle_drop_generation(S0, GenId) ->
     #s{
         shard_id = ShardId,
         db = DB,
-        schema = #{?GEN_KEY(GenId) := GenSchema} = OldSchema,
-        shard = OldShard,
-        cf_refs = OldCFRefs
+        schema = #{?GEN_KEY(GenId) := GenSchema} = Schema0,
+        shard = #{?GEN_KEY(GenId) := #{data := RuntimeData}} = Shard0,
+        cf_refs = CFRefs0
     } = S0,
     %% 1. Commit the metadata first, so other functions are less
     %% likely to see stale data, and replicas don't end up
@@ -800,16 +801,16 @@ handle_drop_generation(S0, GenId) ->
     %%
     %% Note: in theory, this operation may be interrupted in the
     %% middle. This will leave column families hanging.
-    Shard = maps:remove(?GEN_KEY(GenId), OldShard),
-    Schema = maps:remove(?GEN_KEY(GenId), OldSchema),
+    Shard = maps:remove(?GEN_KEY(GenId), Shard0),
+    Schema = maps:remove(?GEN_KEY(GenId), Schema0),
     S1 = S0#s{
         shard = Shard,
         schema = Schema
     },
     commit_metadata(S1),
     %% 2. Now, actually drop the data from RocksDB:
-    #{module := Mod, cf_refs := GenCFRefs} = GenSchema,
-    #{?GEN_KEY(GenId) := #{data := RuntimeData}} = OldShard,
+    #{module := Mod, cf_names := GenCFNames} = GenSchema,
+    GenCFRefs = [cf_ref(Name, CFRefs0) || Name <- GenCFNames],
     try
         Mod:drop(ShardId, DB, GenId, GenCFRefs, RuntimeData)
     catch
@@ -826,7 +827,7 @@ handle_drop_generation(S0, GenId) ->
                 }
             )
     end,
-    CFRefs = OldCFRefs -- GenCFRefs,
+    CFRefs = CFRefs0 -- GenCFRefs,
     S = S1#s{cf_refs = CFRefs},
     {ok, S}.
 
@@ -878,7 +879,7 @@ new_generation(ShardId, DB, Schema0, Shard0, Since) ->
     GenSchema = #{
         module => Mod,
         data => GenData,
-        cf_refs => NewCFRefs,
+        cf_names => cf_names(NewCFRefs),
         created_at => erlang:system_time(millisecond),
         since => Since,
         until => undefined
@@ -964,18 +965,22 @@ update_last_until(Schema = #{current_generation := GenId}, Until) ->
             {error, overlaps_existing_generations}
     end.
 
-handle_flush(S = #s{db = DB, cf_need_flush = NeedFlushGenId, schema = Schema}) ->
+handle_flush(S = #s{db = DB, cf_refs = CFRefs, cf_need_flush = NeedFlushGenId, shard = Shard}) ->
     %% NOTE
     %% There could have been few generations added since the last time `flush/1` was
     %% called. Strictly speaking, we don't need to flush them all at once as part of
     %% a single atomic flush, but the error handling is a bit easier this way.
-    CurrentGenId = maps:get(current_generation, Schema),
+    CurrentGenId = maps:get(current_generation, Shard),
     GenIds = lists:seq(NeedFlushGenId, CurrentGenId),
     CFHandles = lists:flatmap(
         fun(GenId) ->
-            #{?GEN_KEY(GenId) := #{cf_refs := CFRefs}} = Schema,
-            {_, CFHandles} = lists:unzip(CFRefs),
-            CFHandles
+            case Shard of
+                #{?GEN_KEY(GenId) := #{cf_names := CFNames}} ->
+                    [cf_handle(N, CFRefs) || N <- CFNames];
+                #{} ->
+                    %% Generation was probably dropped.
+                    []
+            end
         end,
         GenIds
     ),
@@ -1028,6 +1033,19 @@ mk_write_options(#{durable := false}) ->
 mk_write_options(#{}) ->
     [].
 
+-spec cf_names(cf_refs()) -> [string()].
+cf_names(CFRefs) ->
+    {CFNames, _CFHandles} = lists:unzip(CFRefs),
+    CFNames.
+
+-spec cf_ref(_Name :: string(), cf_refs()) -> cf_ref().
+cf_ref(Name, CFRefs) ->
+    lists:keyfind(Name, 1, CFRefs).
+
+-spec cf_handle(_Name :: string(), cf_refs()) -> rocksdb:cf_handle().
+cf_handle(Name, CFRefs) ->
+    element(2, cf_ref(Name, CFRefs)).
+
 %%--------------------------------------------------------------------------------
 %% Schema access
 %%--------------------------------------------------------------------------------