QQ: tweaks to checkpointing for use cases with fewer larger messages.

Lower the min_checkpoint_interval substantially to allow quorum queues
better control over when checkpoints are taken.

Track bytes enqueued in the aux state and suggest a checkpoint after
every 64MB enqueued. This should help with more timely checkpointing
when very large messages is used.

Author: kjnilsson

deps/rabbit/src/rabbit_fifo.erl

@@ -932,7 +932,7 @@ which_module(5) -> ?MODULE.
                      smallest_index :: undefined | ra:index(),
                      messages_total :: non_neg_integer(),
                      indexes = ?CHECK_MIN_INDEXES :: non_neg_integer(),
-                     unused_1 = ?NIL}).
+                     bytes_in = 0 :: non_neg_integer()}).
 -record(aux_gc, {last_raft_idx = 0 :: ra:index()}).
 -record(aux, {name :: atom(),
               capacity :: term(),
@@ -943,7 +943,9 @@ which_module(5) -> ?MODULE.
                gc = #aux_gc{} :: #aux_gc{},
                tick_pid :: undefined | pid(),
                cache = #{} :: map(),
-               last_checkpoint :: #checkpoint{}}).
+               last_checkpoint :: #checkpoint{},
+               bytes_in = 0 :: non_neg_integer(),
+               bytes_out = 0 :: non_neg_integer()}).
 
 init_aux(Name) when is_atom(Name) ->
     %% TODO: catch specific exception throw if table already exists
@@ -956,7 +958,7 @@ init_aux(Name) when is_atom(Name) ->
           last_checkpoint = #checkpoint{index = 0,
                                         timestamp = erlang:system_time(millisecond),
                                         messages_total = 0,
-                                        unused_1 = ?NIL}}.
+                                        bytes_in = 0}}.
 
 handle_aux(RaftState, Tag, Cmd, #aux{name = Name,
                                      capacity = Cap,
@@ -973,13 +975,14 @@ handle_aux(RaftState, Tag, Cmd, AuxV2, RaAux)
     handle_aux(RaftState, Tag, Cmd, AuxV3, RaAux);
 handle_aux(leader, cast, eval,
            #?AUX{last_decorators_state = LastDec,
+                 bytes_in = BytesIn,
                  last_checkpoint = Check0} = Aux0,
            RaAux) ->
     #?STATE{cfg = #cfg{resource = QName}} = MacState =
         ra_aux:machine_state(RaAux),
 
     Ts = erlang:system_time(millisecond),
-    {Check, Effects0} = do_checkpoints(Ts, Check0, RaAux, false),
+    {Check, Effects0} = do_checkpoints(Ts, Check0, RaAux, BytesIn, false),
 
     %% this is called after each batch of commands have been applied
     %% set timer for message expire
@@ -995,11 +998,16 @@ handle_aux(leader, cast, eval,
                                  last_decorators_state = NewLast}, RaAux, Effects}
     end;
 handle_aux(_RaftState, cast, eval,
-           #?AUX{last_checkpoint = Check0} = Aux0,
+           #?AUX{last_checkpoint = Check0,
+                 bytes_in = BytesIn} = Aux0,
            RaAux) ->
     Ts = erlang:system_time(millisecond),
-    {Check, Effects} = do_checkpoints(Ts, Check0, RaAux, false),
+    {Check, Effects} = do_checkpoints(Ts, Check0, RaAux, BytesIn, false),
     {no_reply, Aux0#?AUX{last_checkpoint = Check}, RaAux, Effects};
+handle_aux(_RaftState, cast, {bytes_in, {MetaSize, BodySize}},
+           #?AUX{bytes_in = Bytes} = Aux0,
+           RaAux) ->
+    {no_reply, Aux0#?AUX{bytes_in = Bytes + MetaSize + BodySize}, RaAux, []};
 handle_aux(_RaftState, cast, {#return{msg_ids = MsgIds,
                                       consumer_key = Key} = Ret, Corr, Pid},
            Aux0, RaAux0) ->
@@ -1129,12 +1137,13 @@ handle_aux(_RaState, {call, _From}, {peek, Pos}, Aux0,
 handle_aux(_, _, garbage_collection, Aux, RaAux) ->
     {no_reply, force_eval_gc(RaAux, Aux), RaAux};
 handle_aux(_RaState, _, force_checkpoint,
-           #?AUX{last_checkpoint  = Check0} = Aux, RaAux) ->
+           #?AUX{last_checkpoint  = Check0,
+                 bytes_in = BytesIn} = Aux, RaAux) ->
     Ts = erlang:system_time(millisecond),
     #?STATE{cfg = #cfg{resource = QR}} = ra_aux:machine_state(RaAux),
     rabbit_log:debug("~ts: rabbit_fifo: forcing checkpoint at ~b",
                      [rabbit_misc:rs(QR), ra_aux:last_applied(RaAux)]),
-    {Check, Effects} = do_checkpoints(Ts, Check0, RaAux, true),
+    {Check, Effects} = do_checkpoints(Ts, Check0, RaAux, BytesIn, true),
     {no_reply, Aux#?AUX{last_checkpoint = Check}, RaAux, Effects};
 handle_aux(RaState, _, {dlx, _} = Cmd, Aux0, RaAux) ->
     #?STATE{dlx = DlxState,
@@ -1578,7 +1587,9 @@ maybe_return_all(#{system_time := Ts} = Meta, ConsumerKey,
 apply_enqueue(#{index := RaftIdx,
                 system_time := Ts} = Meta, From,
               Seq, RawMsg, Size, State0) ->
-    case maybe_enqueue(RaftIdx, Ts, From, Seq, RawMsg, Size, [], State0) of
+    Effects0 = [{aux, {bytes_in, Size}}],
+    case maybe_enqueue(RaftIdx, Ts, From, Seq, RawMsg, Size,
+                       Effects0, State0) of
         {ok, State1, Effects1} ->
             checkout(Meta, State0, State1, Effects1);
         {out_of_sequence, State, Effects} ->
@@ -2918,11 +2929,12 @@ priority_tag(Msg) ->
     end.
 
 
-do_checkpoints(Ts,
-               #checkpoint{index = ChIdx,
-                           timestamp = ChTime,
-                           smallest_index = LastSmallest,
-                           indexes = MinIndexes} = Check0, RaAux, Force) ->
+do_checkpoints(Ts, #checkpoint{index = ChIdx,
+                               timestamp = ChTime,
+                               smallest_index = LastSmallest,
+                               bytes_in = LastBytesIn,
+                               indexes = MinIndexes} = Check0,
+               RaAux, BytesIn, Force) ->
     LastAppliedIdx = ra_aux:last_applied(RaAux),
     IndexesSince = LastAppliedIdx - ChIdx,
     #?STATE{} = MacState = ra_aux:machine_state(RaAux),
@@ -2934,21 +2946,30 @@ do_checkpoints(Ts,
                           Smallest
                   end,
     MsgsTot = messages_total(MacState),
+    %% more than 64MB (by default) of message data has been written to the log
+    %% best take a checkpoint
+    EnoughDataWritten = BytesIn - LastBytesIn > ?CHECK_MAX_BYTES,
+
     {CheckMinInterval, CheckMinIndexes, CheckMaxIndexes} =
         persistent_term:get(quorum_queue_checkpoint_config,
                             {?CHECK_MIN_INTERVAL_MS, ?CHECK_MIN_INDEXES,
                              ?CHECK_MAX_INDEXES}),
     EnoughTimeHasPassed = TimeSince > CheckMinInterval,
 
-    %% enough time has passed and enough indexes have been committed
-    case (IndexesSince > MinIndexes andalso
-          EnoughTimeHasPassed) orelse
-         %% the queue is empty and some commands have been
-         %% applied since the last checkpoint
-         (MsgsTot == 0 andalso
-          IndexesSince > CheckMinIndexes andalso
-          EnoughTimeHasPassed) orelse
-         Force of
+    case EnoughTimeHasPassed andalso
+         (
+          %% condition 1: enough indexes have been committed since the last
+          %% checkpoint
+          (IndexesSince > MinIndexes) orelse
+          %% condition 2: the queue is empty and _some_ commands
+          %% have been applied since the last checkpoint
+          (MsgsTot == 0 andalso IndexesSince > 32) orelse
+          %% condition 3: enough message data has been written to warrant a new
+          %% checkpoint
+          EnoughDataWritten orelse
+          %% force was requested, e.g. after a purge
+          Force
+         ) of
         true ->
             %% take fewer checkpoints the more messages there are on queue
             NextIndexes = min(max(MsgsTot, CheckMinIndexes), CheckMaxIndexes),
@@ -2957,6 +2978,7 @@ do_checkpoints(Ts,
                          timestamp = Ts,
                          smallest_index = NewSmallest,
                          messages_total = MsgsTot,
+                         bytes_in = BytesIn,
                          indexes = NextIndexes},
              [{checkpoint, LastAppliedIdx, MacState} |
               release_cursor(LastSmallest, NewSmallest)]};

deps/rabbit/src/rabbit_fifo.hrl

@@ -100,8 +100,11 @@
 % represents a partially applied module call
 
 -define(CHECK_MIN_INTERVAL_MS, 1000).
--define(CHECK_MIN_INDEXES, 4096).
+-define(CHECK_MIN_INDEXES, 4096 * 2).
 -define(CHECK_MAX_INDEXES, 666_667).
+%% once these many bytes have been written since the last checkpoint
+%% we request a checkpoint irrespectively
+-define(CHECK_MAX_BYTES, 64_000_000).
 
 -define(USE_AVG_HALF_LIFE, 10000.0).
 %% an average QQ without any message uses about 100KB so setting this limit

deps/rabbit/src/rabbit_quorum_queue.erl

@@ -145,8 +145,9 @@
 -define(DELETE_TIMEOUT, 5000).
 -define(MEMBER_CHANGE_TIMEOUT, 20_000).
 -define(SNAPSHOT_INTERVAL, 8192). %% the ra default is 4096
-% -define(UNLIMITED_PREFETCH_COUNT, 2000). %% something large for ra
--define(MIN_CHECKPOINT_INTERVAL, 8192). %% the ra default is 16384
+%% setting a low default here to allow quorum queues to better chose themselves
+%% when to take a checkpoint
+-define(MIN_CHECKPOINT_INTERVAL, 64).
 -define(LEADER_HEALTH_CHECK_TIMEOUT, 5_000).
 -define(GLOBAL_LEADER_HEALTH_CHECK_TIMEOUT, 60_000).
 

deps/rabbit/test/quorum_queue_SUITE.erl

@@ -1527,6 +1527,8 @@ gh_12635(Config) ->
     publish_confirm(Ch0, QQ),
     publish_confirm(Ch0, QQ),
 
+    %% a QQ will not take checkpoints more frequently than every 1s
+    timer:sleep(1000),
     %% force a checkpoint on leader
     ok = rpc:call(Server0, ra, cast_aux_command, [{RaName, Server0}, force_checkpoint]),
     rabbit_ct_helpers:await_condition(