fix(ds): Apply review remarks

apps/emqx_durable_storage/src/emqx_ds.erl

@@ -39,7 +39,10 @@
     message_store_opts/0,
     session_id/0,
     iterator_id/0,
-    iterator/0
+    iterator/0,
+    shard/0,
+    topic/0,
+    time/0
 ]).
 
 -include("emqx_ds_int.hrl").
@@ -62,6 +65,16 @@
 
 -type message_id() :: binary().
 
+%% Parsed topic:
+-type topic() :: list(binary()).
+
+-type shard() :: binary().
+
+%% Timestamp
+%% Earliest possible timestamp is 0.
+%% TODO granularity?
+-type time() :: non_neg_integer().
+
 %%================================================================================
 %% API funcions
 %%================================================================================

apps/emqx_durable_storage/src/emqx_ds_message_storage_bitmask.erl

@@ -38,9 +38,9 @@
 %% to map topics to fixed-length bitstrings while keeping some degree
 %% of information about the hierarchy.
 %%
-%% Next important concept is what we call "epoch". It is time
+%% Next important concept is what we call "epoch". Duration of the
-%% interval determined by the number of least significant bits of the
+%% epoch is determined by maximum time offset. Epoch is calculated by
-%% timestamp found at the tail of the rocksdb key.
+%% shifting bits of the timestamp right.
 %%
 %% The resulting index is a space-filling curve that looks like
 %% this in the topic-time 2D space:

apps/emqx_durable_storage/src/emqx_ds_replay.erl

@@ -6,28 +6,17 @@
 %% API:
 -export([]).
 
--export_type([topic/0, time/0, shard/0]).
 -export_type([replay_id/0, replay/0]).
 
 %%================================================================================
 %% Type declarations
 %%================================================================================
 
-%% parsed
--type topic() :: list(binary()).
-
--type shard() :: binary().
-
-%% Timestamp
-%% Earliest possible timestamp is 0.
-%% TODO granularity?
--type time() :: non_neg_integer().
-
 -type replay_id() :: binary().
 
 -type replay() :: {
-    _TopicFilter :: topic(),
+    _TopicFilter :: emqx_ds:topic(),
-    _StartTime :: time()
+    _StartTime :: emqx_ds:time()
 }.
 
 %%================================================================================