Push priority down into log provider append

Summary:
The follow stack of diffs will implement priority requests (as per [this](https://docs.google.com/document/d/181je6C5Iwmi5Ckl87UPLOug2V0eLVp8jIM2DoDlWbpo/edit?tab=t.0#heading=h.9l8mmncnncc8) doc).

 ---

This diff exposes `Priority` to a log provider's append method. It's a no-op for now.

Reviewed By: jaher

Differential Revision: D83006862

fbshipit-source-id: 46ce9e62fb0eafd3ca6ac434c0a88bddfa58cc9a

Author: patelarjav

src/wa_raft_log.erl

@@ -20,6 +20,7 @@
 -export([
     append/2,
     try_append/2,
+    try_append/3,
     check_heartbeat/3
 ]).
 
@@ -241,7 +242,7 @@
 %%    make it difficult to append to the log without blocking, then
 %%    the append should be skipped and 'skipped' returned. Otherwise,
 %%    the same conditions as the 'strict' mode apply.
--callback append(View :: view(), Entries :: [log_entry() | binary()], Mode :: strict | relaxed) ->
+-callback append(View :: view(), Entries :: [log_entry() | binary()], Mode :: strict | relaxed, Priority :: wa_raft_acceptor:priority()) ->
     ok | skipped | {error, Reason :: term()}.
 
 %%-------------------------------------------------------------------
@@ -326,22 +327,27 @@ start_link(#raft_options{log_name = Name} = Options) ->
     {ok, NewView :: view()} | {error, Reason :: term()}.
 append(View, Entries) ->
     % eqwalizer:ignore - strict append cannot return skipped
-    append(View, Entries, strict).
+    append(View, Entries, strict, high).
 
 %% Attempt to append new log entries to the end of the log if an append can be
 %% serviced immediately.
 -spec try_append(View :: view(), Entries :: [log_entry() | binary()]) ->
     {ok, NewView :: view()} | skipped | {error, Reason :: term()}.
 try_append(View, Entries) ->
-    append(View, Entries, relaxed).
+    try_append(View, Entries, high).
+
+-spec try_append(View :: view(), Entries :: [log_entry() | binary()], Priority :: wa_raft_acceptor:priority()) ->
+    {ok, NewView :: view()} | skipped | {error, Reason :: term()}.
+try_append(View, Entries, Priority) ->
+    append(View, Entries, relaxed, Priority).
 
 %% Append new log entries to the end of the log.
--spec append(View :: view(), Entries :: [log_entry() | binary()], Mode :: strict | relaxed) ->
+-spec append(View :: view(), Entries :: [log_entry() | binary()], Mode :: strict | relaxed, Priority :: wa_raft_acceptor:priority()) ->
     {ok, NewView :: view()} | skipped | {error, Reason :: term()}.
-append(#log_view{last = Last} = View, Entries, Mode) ->
+append(#log_view{last = Last} = View, Entries, Mode, Priority) ->
     ?RAFT_COUNT('raft.log.append'),
     Provider = provider(View),
-    case Provider:append(View, Entries, Mode) of
+    case Provider:append(View, Entries, Mode, Priority) of
         ok ->
             ?RAFT_COUNT('raft.log.append.ok'),
             {ok, refresh_config(View#log_view{last = Last + length(Entries)})};

src/wa_raft_log_ets.erl

@@ -26,7 +26,7 @@
 
 %% RAFT log provider interface for writing new log data
 -export([
-    append/3
+    append/4
 ]).
 
 %% RAFT log provider interface for managing underlying RAFT log
@@ -141,8 +141,8 @@ config(#raft_log{name = Name}) ->
 %% RAFT log provider interface for writing new log data
 %%-------------------------------------------------------------------
 
--spec append(View :: wa_raft_log:view(), Entries :: [wa_raft_log:log_entry() | binary()], Mode :: strict | relaxed) -> ok.
-append(View, Entries, _Mode) ->
+-spec append(View :: wa_raft_log:view(), Entries :: [wa_raft_log:log_entry() | binary()], Mode :: strict | relaxed, Priority :: wa_raft_acceptor:priority()) -> ok.
+append(View, Entries, _Mode, _Priority) ->
     Name = wa_raft_log:log_name(View),
     Last = wa_raft_log:last_index(View),
     true = ets:insert(Name, append_decode(Last + 1, Entries)),

src/wa_raft_server.erl

@@ -2724,7 +2724,7 @@ commit_pending(#raft_state{log_view = View, pending_high = PendingHigh, pending_
         [_ | _] ->
             % If we have processed at least one new log entry
             % with the given priority, we try to append to the log.
-            case wa_raft_log:try_append(View, Entries) of
+            case wa_raft_log:try_append(View, Entries, Priority) of
                 {ok, NewView} ->
                     % Add the newly appended log entries to the pending queue (which
                     % is kept in reverse order).