Merge pull request #281 from rabbitmq/wal-remove-lists-reverse

Remove lists:reverse/1 call in ra_log_wal
rabbitmq · May 18, 2022 · 0459728 · 0459728
2 parents 6fd55eb + ea7bc38
commit 0459728
Showing 1 changed file with 20 additions and 8 deletions.
diff --git a/src/ra_log_wal.erl b/src/ra_log_wal.erl
@@ -454,7 +454,7 @@ append_data(#state{conf = Cfg,
                    writers = Writers} = State,
             {UId, Pid}, Idx, Term, Entry, DataSize, Data, Truncate) ->
     Batch = incr_batch(Cfg, Batch0, UId, Pid,
-                       {Idx, Term}, Data, Entry, Truncate),
+                       {Idx, Term, Entry}, Data, Truncate),
     State#state{file_size = FileSize + DataSize,
                 batch = Batch,
                 writers = Writers#{UId => {in_seq, Idx}} }.
@@ -463,14 +463,29 @@ incr_batch(#conf{open_mem_tbls_name = OpnMemTbl} = Cfg,
            #batch{writes = Writes,
                   waiting = Waiting0,
                   pending = Pend} = Batch,
-           UId, Pid, {Idx, Term}, Data, Entry, Truncate) ->
+           UId, Pid, {Idx, Term, _} = Record, Data, Truncate) ->
     Waiting = case Waiting0 of
                   #{Pid := #batch_writer{tbl_start = TblStart0,
                                          tid = _Tid,
                                          from = From,
                                          inserts = Inserts0} = W} ->
                       TblStart = table_start(Truncate, Idx, TblStart0),
-                      Inserts = [{Idx, Term, Entry} | Inserts0],
+                      Inserts = case Inserts0 of
+                                    [] ->
+                                        [Record];
+                                    [{PrevIdx, _, _} | RemIdxs] when Idx =< PrevIdx ->
+                                        %% we are overwriting, this should rarely,
+                                        %% if ever happen within the timeframe of a batch
+                                        %% Drop all inserts that are higher or equal
+                                        %% to the current Idx
+                                        Filtered =
+                                            lists:dropwhile(fun ({I, _, _}) ->
+                                                                    Idx =< I
+                                                            end, RemIdxs),
+                                        [Record | Filtered];
+                                    _ ->
+                                        [Record | Inserts0]
+                                end,
                       Waiting0#{Pid => W#batch_writer{from = min(Idx, From),
                                                       tbl_start = TblStart,
                                                       to = Idx,
@@ -496,7 +511,7 @@ incr_batch(#conf{open_mem_tbls_name = OpnMemTbl} = Cfg,
                                              tid = Tid,
                                              uid = UId,
                                              term = Term,
-                                             inserts = [{Idx, Term, Entry}]},
+                                             inserts = [Record]},
                       Waiting0#{Pid => Writer}
               end,
 
@@ -720,10 +735,7 @@ complete_batch(#state{batch = #batch{waiting = Waiting,
                               term = Term,
                               inserts = Inserts,
                               tid = Tid}) ->
-              %% need to reverse inserts in case an index overwrite
-              %% came to be processed in the same batch.
-              %% Unlikely, but possible
-              true = ets:insert(Tid, lists:reverse(Inserts)),
+              true = ets:insert(Tid, Inserts),
               true = ets:update_element(OpnTbl, UId,
                                         [{2, TblStart}, {3, To}]),
               Pid ! {ra_log_event, {written, {From, To, Term}}},