Adapt stream code to Osiris read ahead

Osiris can read ahead data in case of small chunks. This saves system
calls and increases consumption rate dramatically for some streams.
This is transparent for the stream protocol, but requires a small tweak
for the stream queue type implementation (passing in the previous
iterator when creating a new one).

The read ahead is on by default but can be deactivated with to the new
stream.read_ahead configuration entry (true / false).

Co-authored-by: Karl Nilsson <kjnilsson@gmail.com>

References rabbitmq/osiris#192

deps/rabbit/Makefile

@@ -119,6 +119,7 @@ define PROJECT_ENV
       	{dead_letter_worker_consumer_prefetch, 32},
       	{dead_letter_worker_publisher_confirm_timeout, 180000},
 		{vhost_process_reconciliation_run_interval, 30},
+		{stream_read_ahead, true},
 		%% for testing
 		{vhost_process_reconciliation_enabled, true},
 		{license_line, "Licensed under the MPL 2.0. Website: https://rabbitmq.com"}

deps/rabbit/priv/schema/rabbit.schema

@@ -2785,6 +2785,9 @@ fun(Conf) ->
     end
 end}.
 
+{mapping, "stream.read_ahead", "rabbit.stream_read_ahead",
+    [{datatype, {enum, [true, false]}}]}.
+
 {mapping, "cluster_tags.$tag", "rabbit.cluster_tags", [
     {datatype, [binary]}
 ]}.

deps/rabbit/src/rabbit_stream_queue.erl

@@ -51,6 +51,7 @@
 -export([format_osiris_event/2]).
 -export([update_stream_conf/2]).
 -export([readers/1]).
+-export([read_ahead_on/0]).
 
 -export([parse_offset_arg/1,
          filter_spec/1]).
@@ -463,10 +464,11 @@ query_local_pid(#stream_client{stream_id = StreamId} = State) ->
 begin_stream(#stream_client{name = QName,
                             readers = Readers0,
                             local_pid = LocalPid} = State,
-             Tag, Offset, Mode, AckRequired, Filter, Options)
+             Tag, Offset, Mode, AckRequired, Filter, Options0)
   when is_pid(LocalPid) ->
     CounterSpec = {{?MODULE, QName, Tag, self()}, []},
-    {ok, Seg0} = osiris:init_reader(LocalPid, Offset, CounterSpec, Options),
+    Options1 = Options0#{read_ahead => read_ahead_on()},
+    {ok, Seg0} = osiris:init_reader(LocalPid, Offset, CounterSpec, Options1),
     NextOffset = osiris_log:next_offset(Seg0) - 1,
     osiris:register_offset_listener(LocalPid, NextOffset),
     StartOffset = case Offset of
@@ -491,7 +493,7 @@ begin_stream(#stream_client{name = QName,
                    last_consumed_offset = StartOffset,
                    log = Seg0,
                    filter = Filter,
-                   reader_options = Options},
+                   reader_options = Options1},
     {ok, State#stream_client{readers = Readers0#{Tag => Str0}}}.
 
 cancel(_Q, #{consumer_tag := ConsumerTag,
@@ -1176,7 +1178,7 @@ stream_entries(QName, Name, CTag, LocalPid,
                        credit = Credit} = Str0) ->
     case Credit > 0 of
         true ->
-            case chunk_iterator(Str0, LocalPid) of
+            case chunk_iterator(Str0, LocalPid, undefined) of
                 {ok, Str} ->
                     stream_entries(QName, Name, CTag, LocalPid, Str);
                 {end_of_stream, Str} ->
@@ -1229,7 +1231,7 @@ stream_entries(QName, Name, CTag, LocalPid,
             gen_server:cast(self(), queue_event(QName, {resume_filtering, CTag})),
             {Str0#stream{filtering_paused = true}, lists:reverse(Acc0)};
         end_of_chunk ->
-            case chunk_iterator(Str0, LocalPid) of
+            case chunk_iterator(Str0, LocalPid, Iter0) of
                 {ok, Str} ->
                     stream_entries(QName, Name, CTag, LocalPid, Str, Acc0);
                 {end_of_stream, Str} ->
@@ -1294,8 +1296,8 @@ stream_entries(QName, Name, CTag, LocalPid,
 
 chunk_iterator(#stream{credit = Credit,
                        listening_offset = LOffs,
-                       log = Log0} = Str0, LocalPid) ->
-    case osiris_log:chunk_iterator(Log0, Credit) of
+                       log = Log0} = Str0, LocalPid, PrevIterator) ->
+    case osiris_log:chunk_iterator(Log0, Credit, PrevIterator) of
         {ok, _ChunkHeader, Iter, Log} ->
             {ok, Str0#stream{chunk_iterator = Iter,
                              log = Log}};
@@ -1527,3 +1529,6 @@ queue_vm_stats_sups() ->
 queue_vm_ets() ->
     {[],
      []}.
+
+read_ahead_on() ->
+    application:get_env(rabbit, stream_read_ahead, true).

deps/rabbit/test/config_schema_SUITE_data/rabbit.snippets

@@ -1223,6 +1223,28 @@ credential_validator.regexp = ^abc\\d+",
    [{osiris, [
       {port_range, {4100, 4600}}
      ]}],
+   []},
+
+  %%
+  %% Stream read ahead on/off
+  %%
+
+  {stream_read_ahead,
+   "
+    stream.read_ahead = true
+   ",
+   [{rabbit, [
+      {stream_read_ahead, true}
+     ]}],
+   []},
+
+  {stream_read_ahead,
+   "
+    stream.read_ahead = false
+   ",
+   [{rabbit, [
+      {stream_read_ahead, false}
+     ]}],
    []}
 
 ].

deps/rabbitmq_stream/src/rabbit_stream_reader.erl

@@ -2812,11 +2812,14 @@ init_reader(ConnectionTransport,
             Properties,
             OffsetSpec) ->
     CounterSpec = {{?MODULE, QueueResource, SubscriptionId, self()}, []},
-    Options = maps:merge(#{transport => ConnectionTransport,
-                           chunk_selector => get_chunk_selector(Properties)},
+    Options0 = #{transport => ConnectionTransport,
+                 chunk_selector => get_chunk_selector(Properties),
+                 read_ahead => rabbit_stream_queue:read_ahead_on()},
+
+    Options1 = maps:merge(Options0,
                           rabbit_stream_utils:filter_spec(Properties)),
-    {ok, Segment} =
-        osiris:init_reader(LocalMemberPid, OffsetSpec, CounterSpec, Options),
+    {ok, Segment} = osiris:init_reader(LocalMemberPid, OffsetSpec,
+                                       CounterSpec, Options1),
     ?LOG_DEBUG("Next offset for subscription ~tp is ~tp",
                      [SubscriptionId, osiris_log:next_offset(Segment)]),
     Segment.

deps/rabbitmq_stream/test/rabbit_stream_SUITE.erl

@@ -19,6 +19,7 @@
 
 -include_lib("eunit/include/eunit.hrl").
 -include_lib("rabbit_common/include/rabbit.hrl").
+-include_lib("amqp10_common/include/amqp10_framing.hrl").
 -include_lib("rabbitmq_ct_helpers/include/rabbit_assert.hrl").
 -include_lib("rabbitmq_stream_common/include/rabbit_stream.hrl").
 
@@ -1773,3 +1774,9 @@ request(CorrId, Cmd) ->
 
 rand_bin() ->
     base64:encode(rand:bytes(20)).
+
+generate_log(MsgSize, MsgsPerChunk, NumMessages, Directory) ->
+    Body = binary:copy(<<"a">>, MsgSize),
+    Data = #'v1_0.data'{content = Body},
+    Bin = amqp10_framing:encode_bin(Data),
+    osiris_log:generate_log(Bin, MsgsPerChunk, NumMessages, Directory).