[GitHub] nickva commented on a change in pull request #484: Apply random jitter during initial _replicator shard discovery

[gi...@git.apache.org]

nickva commented on a change in pull request #484: Apply random jitter during initial _replicator shard discovery
URL: https://github.com/apache/couchdb/pull/484#discussion_r115071338
 
 

 ##########
 File path: src/couch/src/couch_multidb_changes.erl
 ##########
 @@ -257,40 +257,54 @@ scan_all_dbs(Server, DbSuffix) when is_pid(Server) ->
     {ok, Db} = mem3_util:ensure_exists(
         config:get("mem3", "shards_db", "_dbs")),
     ChangesFun = couch_changes:handle_changes(#changes_args{}, nil, Db, nil),
-    ChangesFun(fun({change, {Change}, _}, _) ->
-        DbName = couch_util:get_value(<<"id">>, Change),
-        case DbName of
-            <<"_design/", _/binary>> ->
-                ok;
-            _Else ->
-                case couch_replicator_utils:is_deleted(Change) of
-                    true ->
-                        ok;
-                    false ->
-                        [gen_server:cast(Server, {resume_scan, ShardName})
-                         || ShardName <- filter_shards(DbName, DbSuffix)],
-                        ok
-                end
-        end;
-        (_, _) -> ok
-    end),
+    ChangesFun({fun scan_changes_cb/3, {Server, DbSuffix, 1}}),
     couch_db:close(Db).
 
 
-filter_shards(DbName, DbSuffix) ->
-    case DbSuffix =:= couch_db:dbname_suffix(DbName) of
-    false ->
-        [];
-    true ->
-        try
-            [ShardName || #shard{name = ShardName} <- mem3:local_shards(DbName)]
-        catch
-            error:database_does_not_exist ->
-                []
+scan_changes_cb({change, {Change}, _}, _, {_Server, DbSuffix, _Count} = Acc) ->
+    DbName = couch_util:get_value(<<"id">>, Change),
+    case DbName of <<"_design/", _/binary>> -> Acc; _Else ->
+        NameMatch = DbSuffix =:= couch_db:dbname_suffix(DbName),
+        case {NameMatch, couch_replicator_utils:is_deleted(Change)} of
+            {false, _} ->
+                Acc;
+            {true, true} ->
+                Acc;
+            {true, false} ->
+                Shards = local_shards(DbName),
+                lists:foldl(fun notify_fold/2, Acc, Shards)
         end
+    end;
+scan_changes_cb(_, _, Acc) ->
+    Acc.
+
+
+local_shards(DbName) ->
+    try
+        [ShardName || #shard{name = ShardName} <- mem3:local_shards(DbName)]
+    catch
+        error:database_does_not_exist ->
+            []
     end.
 
 
+notify_fold(DbName, {Server, DbSuffix, Count}) ->
+    Jitter = jitter(Count),
+    spawn_link(fun() ->
 
 Review comment:
   In this case we don't see it because it runs in the main server process. If it was running in side the spawned process we'd need to seed it.
 
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