refactor(ds): Implement drop_db function

apps/emqx_durable_storage/src/emqx_ds.erl

@@ -22,7 +22,7 @@
 -module(emqx_ds).
 
 %% Management API:
--export([open_db/2]).
+-export([open_db/2, drop_db/1]).
 
 %% Message storage API:
 -export([store_batch/1, store_batch/2, store_batch/3]).
@@ -50,7 +50,7 @@
 %% Type declarations
 %%================================================================================
 
--type db() :: emqx_ds_replication_layer:db().
+-type db() :: atom().
 
 %% Parsed topic.
 -type topic() :: list(binary()).
@@ -101,6 +101,12 @@
 open_db(DB, Opts) ->
     emqx_ds_replication_layer:open_db(DB, Opts).
 
+%% @doc TODO: currently if one or a few shards are down, they won't be
+%% deleted.
+-spec drop_db(db()) -> ok.
+drop_db(DB) ->
+    emqx_ds_replication_layer:drop_db(DB).
+
 -spec store_batch([emqx_types:message()]) -> store_batch_result().
 store_batch(Msgs) ->
     store_batch(?DEFAULT_DB, Msgs, #{}).
@@ -124,7 +130,15 @@ store_batch(DB, Msgs) ->
 %% reflects the notion that different topics can be stored
 %% differently, but hides the implementation details.
 %%
-%% Rules:
+%% While having to work with multiple iterators to replay a topic
+%% filter may be cumbersome, it opens up some possibilities:
+%%
+%% 1. It's possible to parallelize replays
+%%
+%% 2. Streams can be shared between different clients to implement
+%% shared subscriptions
+%%
+%% IMPORTANT RULES:
 %%
 %% 0. There is no 1-to-1 mapping between MQTT topics and streams. One
 %% stream can contain any number of MQTT topics.
@@ -145,8 +159,8 @@ store_batch(DB, Msgs) ->
 %% equal, then the streams are independent.
 %%
 %% Stream is fully consumed when `next/3' function returns
-%% `end_of_stream'. Then the client can proceed to replaying streams
-%% that depend on the given one.
+%% `end_of_stream'. Then and only then the client can proceed to
+%% replaying streams that depend on the given one.
 -spec get_streams(db(), topic_filter(), time()) -> [{stream_rank(), stream()}].
 get_streams(DB, TopicFilter, StartTime) ->
     emqx_ds_replication_layer:get_streams(DB, TopicFilter, StartTime).

apps/emqx_durable_storage/src/emqx_ds_replication_layer.erl

@@ -18,6 +18,7 @@
 -export([
     list_shards/1,
     open_db/2,
+    drop_db/1,
     store_batch/3,
     get_streams/3,
     make_iterator/2,
@@ -27,6 +28,7 @@
 %% internal exports:
 -export([
     do_open_shard_v1/2,
+    do_drop_shard_v1/1,
     do_get_streams_v1/3,
     do_make_iterator_v1/3,
     do_next_v1/3
@@ -38,9 +40,9 @@
 %% Type declarations
 %%================================================================================
 
--type db() :: binary().
+-type db() :: emqx_ds:db().
 
--type shard_id() :: binary().
+-type shard_id() :: {emqx_ds:db(), atom()}.
 
 %% This record enapsulates the stream entity from the replication
 %% level.
@@ -90,6 +92,16 @@ open_db(DB, Opts) ->
         list_nodes()
     ).
 
+-spec drop_db(emqx_ds:db()) -> ok | {error, _}.
+drop_db(DB) ->
+    lists:foreach(
+        fun(Node) ->
+            Shard = shard_id(DB, Node),
+            ok = emqx_ds_proto_v1:drop_shard(Node, Shard)
+        end,
+        list_nodes()
+    ).
+
 -spec store_batch(emqx_ds:db(), [emqx_types:message()], emqx_ds:message_store_opts()) ->
     emqx_ds:store_batch_result().
 store_batch(DB, Msg, Opts) ->
@@ -163,6 +175,10 @@ next(Iter0, BatchSize) ->
 do_open_shard_v1(Shard, Opts) ->
     emqx_ds_storage_layer:open_shard(Shard, Opts).
 
+-spec do_drop_shard_v1(shard_id()) -> ok.
+do_drop_shard_v1(Shard) ->
+    emqx_ds_storage_layer:drop_shard(Shard).
+
 -spec do_get_streams_v1(shard_id(), emqx_ds:topic_filter(), emqx_ds:time()) ->
     [{integer(), _Stream}].
 do_get_streams_v1(Shard, TopicFilter, StartTime) ->
@@ -187,13 +203,11 @@ add_shard_to_rank(Shard, RankY) ->
 shard_id(DB, Node) ->
     %% TODO: don't bake node name into the schema, don't repeat the
     %% Mnesia's 1M$ mistake.
-    NodeBin = atom_to_binary(Node),
-    <<DB/binary, ":", NodeBin/binary>>.
+    {DB, Node}.
 
 -spec node_of_shard(shard_id()) -> node().
-node_of_shard(ShardId) ->
-    [_DB, NodeBin] = binary:split(ShardId, <<":">>),
-    binary_to_atom(NodeBin).
+node_of_shard({_DB, Node}) ->
+    Node.
 
 list_nodes() ->
     mria:running_nodes().

apps/emqx_durable_storage/src/emqx_ds_storage_layer.erl

@@ -18,13 +18,13 @@
 -behaviour(gen_server).
 
 %% Replication layer API:
--export([open_shard/2, store_batch/3, get_streams/3, make_iterator/3, next/3]).
+-export([open_shard/2, drop_shard/1, store_batch/3, get_streams/3, make_iterator/3, next/3]).
 
 %% gen_server
 -export([start_link/2, init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2]).
 
 %% internal exports:
--export([]).
+-export([drop_shard/1]).
 
 -export_type([gen_id/0, generation/0, cf_refs/0, stream/0, iterator/0]).
 
@@ -124,6 +124,11 @@
 open_shard(Shard, Options) ->
     emqx_ds_storage_layer_sup:ensure_shard(Shard, Options).
 
+-spec drop_shard(shard_id()) -> ok.
+drop_shard(Shard) ->
+    emqx_ds_storage_layer_sup:stop_shard(Shard),
+    ok = rocksdb:destroy(db_dir(Shard), []).
+
 -spec store_batch(shard_id(), [emqx_types:message()], emqx_ds:message_store_opts()) ->
     emqx_ds:store_batch_result().
 store_batch(Shard, Messages, Options) ->
@@ -188,7 +193,7 @@ next(Shard, Iter = #it{generation = GenId, enc = GenIter0}, BatchSize) ->
 
 -define(REF(ShardId), {via, gproc, {n, l, {?MODULE, ShardId}}}).
 
--spec start_link(emqx_ds:shard_id(), emqx_ds:create_db_opts()) ->
+-spec start_link(shard_id(), emqx_ds:create_db_opts()) ->
     {ok, pid()}.
 start_link(Shard, Options) ->
     gen_server:start_link(?REF(Shard), ?MODULE, {Shard, Options}, []).
@@ -303,13 +308,12 @@ commit_metadata(#s{shard_id = ShardId, schema = Schema, shard = Runtime, db = DB
 -spec rocksdb_open(shard_id(), emqx_ds:create_db_opts()) ->
     {ok, rocksdb:db_handle(), cf_refs()} | {error, _TODO}.
 rocksdb_open(Shard, Options) ->
-    DefaultDir = binary_to_list(Shard),
-    DBDir = unicode:characters_to_list(maps:get(dir, Options, DefaultDir)),
     DBOptions = [
         {create_if_missing, true},
         {create_missing_column_families, true}
         | maps:get(db_options, Options, [])
     ],
+    DBDir = db_dir(Shard),
     _ = filelib:ensure_dir(DBDir),
     ExistingCFs =
         case rocksdb:list_column_families(DBDir, DBOptions) of
@@ -331,6 +335,10 @@ rocksdb_open(Shard, Options) ->
             Error
     end.
 
+-spec db_dir(shard_id()) -> file:filename().
+db_dir({DB, ShardId}) ->
+    lists:flatten([atom_to_list(DB), $:, atom_to_list(ShardId)]).
+
 %%--------------------------------------------------------------------------------
 %% Schema access
 %%--------------------------------------------------------------------------------

apps/emqx_durable_storage/src/emqx_ds_storage_reference.erl

@@ -98,13 +98,14 @@ make_iterator(_Shard, _Data, #stream{topic_filter = TopicFilter}, StartTime) ->
 next(_Shard, #s{db = DB, cf = CF}, It0, BatchSize) ->
     #it{topic_filter = TopicFilter, start_time = StartTime, last_seen_message_key = Key0} = It0,
     {ok, ITHandle} = rocksdb:iterator(DB, CF, []),
-    Action = case Key0 of
-                 first ->
-                     first;
-                 _ ->
-                     rocksdb:iterator_move(ITHandle, Key0),
-                     next
-             end,
+    Action =
+        case Key0 of
+            first ->
+                first;
+            _ ->
+                rocksdb:iterator_move(ITHandle, Key0),
+                next
+        end,
     {Key, Messages} = do_next(TopicFilter, StartTime, ITHandle, Action, BatchSize, Key0, []),
     rocksdb:iterator_close(ITHandle),
     It = It0#it{last_seen_message_key = Key},

apps/emqx_durable_storage/src/proto/emqx_ds_proto_v1.erl

@@ -19,7 +19,7 @@
 
 -include_lib("emqx/include/bpapi.hrl").
 %% API:
--export([open_shard/3, get_streams/4, make_iterator/4, next/4]).
+-export([open_shard/3, drop_shard/2, get_streams/4, make_iterator/4, next/4]).
 
 %% behavior callbacks:
 -export([introduced_in/0]).
@@ -33,6 +33,11 @@
 open_shard(Node, Shard, Opts) ->
     erpc:call(Node, emqx_ds_replication_layer, do_open_shard_v1, [Shard, Opts]).
 
+-spec drop_shard(node(), emqx_ds_replication_layer:shard()) ->
+    ok.
+drop_shard(Node, Shard) ->
+    erpc:call(Node, emqx_ds_replication_layer, do_drop_shard_v1, [Shard]).
+
 -spec get_streams(
     node(), emqx_ds_replication_layer:shard(), emqx_ds:topic_filter(), emqx_ds:time()
 ) ->

apps/emqx_durable_storage/test/emqx_ds_SUITE.erl

@@ -22,15 +22,18 @@
 -include_lib("common_test/include/ct.hrl").
 -include_lib("stdlib/include/assert.hrl").
 
-%% A simple smoke test that verifies that opening the DB doesn't crash
-t_00_smoke_open(_Config) ->
-    ?assertMatch(ok, emqx_ds:open_db(<<"DB1">>, #{})),
-    ?assertMatch(ok, emqx_ds:open_db(<<"DB1">>, #{})).
+%% A simple smoke test that verifies that opening/closing the DB
+%% doesn't crash
+t_00_smoke_open_drop(_Config) ->
+    DB = 'DB',
+    ?assertMatch(ok, emqx_ds:open_db(DB, #{})),
+    ?assertMatch(ok, emqx_ds:open_db(DB, #{})),
+    ?assertMatch(ok, emqx_ds:drop_db(DB)).
 
 %% A simple smoke test that verifies that storing the messages doesn't
 %% crash
 t_01_smoke_store(_Config) ->
-    DB = <<"default">>,
+    DB = default,
     ?assertMatch(ok, emqx_ds:open_db(DB, #{})),
     Msg = message(<<"foo/bar">>, <<"foo">>, 0),
     ?assertMatch(ok, emqx_ds:store_batch(DB, [Msg])).
@@ -38,7 +41,7 @@ t_01_smoke_store(_Config) ->
 %% A simple smoke test that verifies that getting the list of streams
 %% doesn't crash and that iterators can be opened.
 t_02_smoke_get_streams_start_iter(_Config) ->
-    DB = <<"default">>,
+    DB = ?FUNCTION_NAME,
     ?assertMatch(ok, emqx_ds:open_db(DB, #{})),
     StartTime = 0,
     [{Rank, Stream}] = emqx_ds:get_streams(DB, ['#'], StartTime),
@@ -48,7 +51,7 @@ t_02_smoke_get_streams_start_iter(_Config) ->
 %% A simple smoke test that verifies that it's possible to iterate
 %% over messages.
 t_03_smoke_iterate(_Config) ->
-    DB = atom_to_binary(?FUNCTION_NAME),
+    DB = ?FUNCTION_NAME,
     ?assertMatch(ok, emqx_ds:open_db(DB, #{})),
     StartTime = 0,
     Msgs = [