Consider the nursery full when it is just below the threshold so we don't overflow the bloom filter.

src/hanoidb_nursery.erl

@@ -130,15 +130,14 @@ do_add(Nursery=#nursery{log_file=File, cache=Cache, total_size=TotalSize, count=
 
     ok = file:write(File, Data),
     Nursery1 = do_sync(File, Nursery),
-
     {ok, Nursery2} = do_inc_merge(Nursery1#nursery{ cache=Cache2,
                                                     total_size=TotalSize + erlang:iolist_size(Data),
                                                     count=Count + 1 }, 1, Top),
-
-    if Count+1 >= ?BTREE_SIZE(?TOP_LEVEL) ->
-            {full, Nursery2};
-       true ->
-            {ok, Nursery2}
+    case has_room(Nursery2, 1) of
+        true ->
+            {ok, Nursery2};
+        false ->
+            {full, Nursery2}
     end.
 
 do_sync(File, Nursery) ->
@@ -257,7 +256,7 @@ flush(Nursery=#nursery{ dir=Dir, max_level=MaxLevel, config=Config }, Top) ->
     hanoidb_nursery:new(Dir, MaxLevel, Config).
 
 has_room(#nursery{ count=Count }, N) ->
-    (Count+N) < ?BTREE_SIZE(?TOP_LEVEL).
+    (Count + N + 1) < ?BTREE_SIZE(?TOP_LEVEL).
 
 ensure_space(Nursery, NeededRoom, Top) ->
     case has_room(Nursery, NeededRoom) of

src/hanoidb_writer.erl

@@ -211,6 +211,12 @@ flush_nodes(#state{ nodes=[], last_node_pos=LastNodePos, last_node_size=_LastNod
     ok = file:close(IdxFile),
 
     {ok, State#state{ index_file=undefined, index_file_pos=undefined }};
+
+flush_nodes(State=#state{ nodes=[#node{level=N, members=[{_,{Pos,_Len}}]}], last_node_pos=Pos })
+  when N > 0 ->
+    %% Ignore this node, its stack consists of one node with one {pos,len} member
+    flush_nodes(State#state{ nodes=[] });
+
 flush_nodes(State) ->
     {ok, State2} = close_node(State),
     flush_nodes(State2).