Merge pull request #195 from rabbitmq/md/timestamp-skip-search

osiris_log: Use index skip search for timestamp offset specs

Author: kjnilsson

src/osiris_log.erl

@@ -2723,31 +2723,40 @@ open(File, Options) ->
     throw_missing(file:open(File, Options)).
 
 chunk_location_for_timestamp(Idx, Ts) ->
-    %% TODO: optimise using skip search approach
-    Fd = open_index_read(Idx),
-    %% scan index file for nearest timestamp
-    {ChunkId, _Timestamp, _Epoch, FilePos} = timestamp_idx_scan(Fd, Ts),
+    {ok, IdxFd} = open(Idx, [read, raw, binary]),
+    _ = file:advise(IdxFd, 0, 0, random),
+    {Ts, {ChunkId, _Timestamp, _Epoch, FilePos}} =
+        idx_skip_search(IdxFd, ?IDX_HEADER_SIZE,
+                        fun timestamp_search_fun/3,
+                        {Ts, not_found}),
+    ok = file:close(IdxFd),
     {ChunkId, FilePos}.
 
-timestamp_idx_scan(Fd, Ts) ->
-    case file:read(Fd, ?INDEX_RECORD_SIZE_B) of
-        {ok,
-         <<ChunkId:64/unsigned,
-           Timestamp:64/signed,
-           Epoch:64/unsigned,
-           FilePos:32/unsigned,
-           _ChType:8/unsigned>>} ->
-            case Ts =< Timestamp of
-                true ->
-                    ok = file:close(Fd),
-                    {ChunkId, Timestamp, Epoch, FilePos};
-                false ->
-                    timestamp_idx_scan(Fd, Ts)
-            end;
-        eof ->
-            ok = file:close(Fd),
-            eof
-    end.
+%% NOTE: this is slightly different than offset_search_fun/3. When searching
+%% for offsets, if the given offset is not a chunk ID then the search returns
+%% the chunk ID less than the given offset. When searching for timestamps,
+%% if the given timestamp is between the timestamp of two chunks, the later
+%% chunk is returned.
+timestamp_search_fun(scan, <<ChunkId:64/unsigned,
+                             Timestamp:64/signed,
+                             Epoch:64/unsigned,
+                             FilePos:32/unsigned,
+                             _ChType:8/unsigned>>, {Ts, _})
+  when Ts =< Timestamp ->
+    {return, {Ts, {ChunkId, Timestamp, Epoch, FilePos}}};
+timestamp_search_fun(peek, <<_ChunkId:64/unsigned,
+                             Timestamp:64/signed,
+                             _Epoch:64/unsigned,
+                             _FilePos:32/unsigned,
+                             _ChType:8/unsigned>>, {Ts, _} = State)
+  when Ts =< Timestamp ->
+    {scan, State};
+timestamp_search_fun(_Type, <<ChunkId:64/unsigned,
+                              Timestamp:64/signed,
+                              Epoch:64/unsigned,
+                              FilePos:32/unsigned,
+                              _ChType:8/unsigned>>, {Ts, _}) ->
+    {continue, {Ts, {ChunkId, Timestamp, Epoch, FilePos}}}.
 
 validate_crc(ChunkId, Crc, IOData) ->
     case erlang:crc32(IOData) of