diff --git a/apps/emqx_replay/src/emqx_replay_message_storage.erl b/apps/emqx_replay/src/emqx_replay_message_storage.erl
index ccacb3ee7..45ad2beab 100644
--- a/apps/emqx_replay/src/emqx_replay_message_storage.erl
+++ b/apps/emqx_replay/src/emqx_replay_message_storage.erl
@@ -1,5 +1,5 @@
 %%--------------------------------------------------------------------
-%% Copyright (c) 2020-2022 EMQ Technologies Co., Ltd. All Rights Reserved.
+%% Copyright (c) 2022 EMQ Technologies Co., Ltd. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -16,11 +16,21 @@
 
 -module(emqx_replay_message_storage).
 
--export([open/2]).
+%% API:
+-export([open/2, close/1]).
 
 -export([store/5]).
 -export([make_iterator/3]).
 
+%% Debug/troubleshooting:
+-export([make_message_key/3, compute_topic_hash/1, hash/2, combine/3]).
+
+-export_type([db/0, iterator/0]).
+
+%%================================================================================
+%% Type declarations
+%%================================================================================
+
 %% see rocksdb:db_options()
 -type options() :: proplists:proplist().
 
@@ -34,29 +44,64 @@
     db :: rocksdb:db_handle()
 }).
 
+-record(it, {
+    handle :: rocksdb:itr_handle(),
+    topic_filter :: emqx_topic:words(),
+    bitmask :: integer(),
+    start_time :: time()
+}).
+
 -opaque db() :: #db{}.
--opaque iterator() :: _TODO.
+
+-opaque iterator() :: #it{}.
+
+%%================================================================================
+%% API funcions
+%%================================================================================
 
 -spec open(file:filename_all(), options()) ->
     {ok, db()} | {error, _TODO}.
 open(Filename, Options) ->
-    #db{
-        db = rocksdb:open(Filename, Options)
-    }.
+    case rocksdb:open(Filename, [{create_if_missing, true}, Options]) of
+        {ok, Handle} ->
+            {ok, #db{db = Handle}};
+        Error ->
+            Error
+    end.
+
+-spec close(db()) -> ok | {error, _}.
+close(#db{db = DB}) ->
+    rocksdb:close(DB).
 
 -spec store(db(), emqx_guid:guid(), time(), topic(), binary()) ->
     ok.
-store(DB, MessageID, PublishedAt, Topic, MessagePayload) ->
+store(#db{db = DB}, MessageID, PublishedAt, Topic, MessagePayload) ->
     Key = make_message_key(MessageID, Topic, PublishedAt),
     Value = make_message_value(Topic, MessagePayload),
     rocksdb:put(DB, Key, Value, [{sync, true}]).
 
--spec make_iterator(db(), emqx_topic:words(), time()) ->
+-spec make_iterator(db(), emqx_topic:words(), time() | earliest) ->
     {ok, iterator()} | {error, invalid_start_time}.
-make_iterator(DB, TopicFilter, StartTime) ->
+make_iterator(#db{db = DBHandle}, TopicFilter, StartTime) ->
+    case rocksdb:iterator(DBHandle, []) of
+        {ok, ITHandle} ->
+            #it{
+                handle = ITHandle,
+                topic_filter = TopicFilter,
+                start_time = StartTime,
+                bitmask = make_bitmask(TopicFilter)
+            };
+        Err ->
+            Err
+    end.
+
+-spec next(iterator()) -> {value, binary()} | none.
+next(It) ->
     error(noimpl).
 
-%%
+%%================================================================================
+%% Internal exports
+%%================================================================================
 
 -define(TOPIC_LEVELS_ENTROPY_BITS, [8, 8, 32, 16]).
 
@@ -72,16 +117,53 @@ combine(TopicHash, PublishedAt, MessageID) ->
 compute_topic_hash(Topic) ->
     compute_topic_hash(Topic, ?TOPIC_LEVELS_ENTROPY_BITS, 0).
 
-compute_topic_hash([], [Bits | BitsRest], Acc) ->
-    Hash = hash(<<"/">>, Bits),
-    compute_topic_hash([], BitsRest, Acc bsl Bits + Hash);
+hash(Input, Bits) ->
+    % at most 32 bits
+    erlang:phash2(Input, 1 bsl Bits).
+
+-spec make_bitmask(emqx_topic:words()) -> integer().
+make_bitmask(TopicFilter) ->
+    make_bitmask(TopicFilter, ?TOPIC_LEVELS_ENTROPY_BITS).
+
+%%================================================================================
+%% Internal functions
+%%================================================================================
+
 compute_topic_hash(LevelsRest, [Bits], Acc) ->
     Hash = hash(LevelsRest, Bits),
     Acc bsl Bits + Hash;
+compute_topic_hash([], [Bits | BitsRest], Acc) ->
+    Hash = hash(<<"/">>, Bits),
+    compute_topic_hash([], BitsRest, Acc bsl Bits + Hash);
 compute_topic_hash([Level | LevelsRest], [Bits | BitsRest], Acc) ->
     Hash = hash(Level, Bits),
     compute_topic_hash(LevelsRest, BitsRest, Acc bsl Bits + Hash).
 
-hash(Input, Bits) ->
-    % at most 32 bits
-    erlang:phash2(Input, 1 bsl Bits).
+make_bitmask(LevelsRest, [Bits], Acc) ->
+    Hash = hash(LevelsRest, Bits),
+    Acc bsl Bits + Hash;
+make_bitmask([], [Bits | BitsRest], Acc) ->
+    Hash = hash(<<"/">>, Bits),
+    make_bitmask([], BitsRest, Acc bsl Bits + Hash);
+make_bitmask([Level | LevelsRest], [Bits | BitsRest], Acc) ->
+    Hash = case Level of
+               '+' ->
+                   0;
+               Bin when is_binary(Bin) ->
+                   1 bsl Bits - 1;
+
+    Hash = hash(Level, Bits),
+    make_bitmask(LevelsRest, BitsRest, Acc bsl Bits + Hash).
+
+%% |123|345|678|
+%%  foo bar baz
+
+%% |123|000|678| - |123|fff|678|
+
+%%  foo +   baz
+
+%% |fff|000|fff|
+
+%% |123|000|678|
+
+%% |123|056|678| & |fff|000|fff| = |123|000|678|.