diff --git a/Makefile b/Makefile
index 58140af..f84d2f2 100644
--- a/Makefile
+++ b/Makefile
@@ -39,4 +39,4 @@ noasan: $(ROOT_IFACE_DBG) build/imgui.o
 	$(MOLD) $(CXX) -DDEBUG -g -O0 $(CFLAGS) -fsanitize=undefined $(INC) $(ROOTFLAGS) -o rntviewer src/rntviewer.cpp build/imgui.o $(ROOT_IFACE_DBG) $(LIBS) $(ROOTLIBS)
 
 r: $(ROOT_IFACE) build/imgui.o
-	$(MOLD) $(CXX) -O2 $(CFLAGS) $(INC) $(ROOTFLAGS) -o rntviewer src/rntviewer.cpp build/imgui.o $(ROOT_IFACE) $(LIBS) $(ROOTLIBS)
+	$(MOLD) $(CXX) -O2 -DNDEBUG $(CFLAGS) $(INC) $(ROOTFLAGS) -o rntviewer src/rntviewer.cpp build/imgui.o $(ROOT_IFACE) $(LIBS) $(ROOTLIBS)
diff --git a/src/render.cpp b/src/render.cpp
index 041a1ac..0c7ee97 100644
--- a/src/render.cpp
+++ b/src/render.cpp
@@ -61,6 +61,7 @@ u32 mem_edit_bg_color_fn(const u8 *, u64 off, void *user_data)
   // printf("%lu vs %lu\n", off, rdata.page_groups[rdata.n_page_groups - 1].range.end());
   for (Page_Info_Chunk *chunk = rdata.page_chunks; chunk; chunk = chunk->next) {
     if (chunk->range.start <= off && off <= chunk->range.end()) {
+      printf("slow path for 0x%lX (last pinfo: 0x%lX - 0x%lX)\n", off, app->last_pinfo->range.start, app->last_pinfo->range.end());
       for (u64 group_idx = chunk->first_group; group_idx < rdata.n_page_groups; ++group_idx) {
         const Page_Info_Group &group = rdata.page_groups[group_idx];
         if (off < group.range.start || off > group.range.end()) 
@@ -74,6 +75,10 @@ u32 mem_edit_bg_color_fn(const u8 *, u64 off, void *user_data)
           }
         }
       }
+
+      fprintf(stderr, "Offset 0x%lX is in chunk 0x%lX - 0x%lX, but found in no page_info range!\n", 
+              off, chunk->range.start, chunk->range.end());
+      assert(false);
     }
   }
 #undef COL
@@ -166,6 +171,7 @@ void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
       assert(app.vsettings.base_display_addr < app.inspected_file_size);
       void *content = app.inspected_fmem + app.vsettings.base_display_addr;
       u64 content_size = app.inspected_file_size - app.vsettings.base_display_addr;
+      app.last_pinfo = &invalid_pinfo;
       mem_edit.DrawContents(content, content_size, app.vsettings.base_display_addr);
 
       ImGui::TableNextColumn();
diff --git a/src/rntuple.cpp b/src/rntuple.cpp
index e2798fa..a748fe0 100644
--- a/src/rntuple.cpp
+++ b/src/rntuple.cpp
@@ -77,9 +77,9 @@ void gather_metadata(Arena *arena, RMicroFileReader &reader, const RNTuple_File_
   
   // for all clusters, gather page metadata
   for (const RClusterDescriptor &cluster_desc : descriptor.GetClusterIterable()) {
-    for (const auto &[col_id, col_range] : cluster_desc.GetColumnRangeIterable()) {
+    for (const RClusterDescriptor::RColumnRange &col_range : cluster_desc.GetColumnRangeIterable()) {
       // insert page infos sorted by byte range
-      const auto &page_range = cluster_desc.GetPageRange(col_id);
+      const auto &page_range = cluster_desc.GetPageRange(col_range.fPhysicalColumnId);
       for (const auto &page_info : page_range.fPageInfos) {
         Page_Info_Node *pinfo = arena_push<Page_Info_Node>(arena);
         pinfo->range.start = page_info.fLocator.GetPosition<u64>(); 
@@ -113,10 +113,12 @@ void gather_metadata(Arena *arena, RMicroFileReader &reader, const RNTuple_File_
 
   fprintf(stderr, "Loaded %lu pages.\nGenerating groups...", n_pages);
 
-  // Create page groups.
+  // Create page groups and chunks.
   // Each page group is a grouping of GROUP_SIZE page infos whose range is equal to the combined ranges
   // of its components. It is an acceleration structure used to more quickly find the correct page info
   // that an offset belongs to.
+  // A page chunk is a grouping of adjacent page groups, used to quickly determine if an offset is part
+  // of a page or not.
   const u64 GROUP_SIZE = 100;
   Page_Info_Group *groups = arena_push_array_nozero<Page_Info_Group>(arena, n_pages / GROUP_SIZE + 1);
   Page_Info_Node *last = nullptr;
@@ -125,39 +127,44 @@ void gather_metadata(Arena *arena, RMicroFileReader &reader, const RNTuple_File_
   u64 n_groups = 0;
   u64 n_chunks = 0;
   for (Page_Info_Node *pinfo = pinfo_head; pinfo; pinfo = pinfo->next) {
-    if (idx++ % GROUP_SIZE == 0) {
-      Page_Info_Group &cur_group = groups[n_groups];
-      cur_group.first = pinfo;
-      cur_group.range.start = pinfo->range.start;
-      if (n_groups > 1) {
-        Page_Info_Group &prev_group = groups[n_groups - 1];
-        prev_group.range.len = cur_group.range.start - prev_group.range.start;
-      }
-
-      assert((!chunks_head) ^ (n_groups > 0));
-
-      if (!chunks_head) { 
-        assert(!chunks_tail);
-        chunks_head = chunks_tail = arena_push<Page_Info_Chunk>(arena);
-        chunks_head->range.start = cur_group.range.start;
-        ++n_chunks;
-      } else if (groups[n_groups - 1].range.end() != cur_group.range.start) {    
-        // close current chunk
-        Page_Info_Group &prev_group = groups[n_groups - 1];
-        chunks_tail->range.len = (prev_group.range.end() - chunks_tail->range.start);
-        // open new chunk
-        Page_Info_Chunk *chunk = arena_push<Page_Info_Chunk>(arena);
-        chunk->range.start = cur_group.range.start;
-        chunks_tail->next = chunk;
-        chunks_tail = chunk;
-        ++n_chunks;
-      } else {
-        chunks_tail->range.len += cur_group.range.len;
-      }
-
-      ++n_groups;
-    }
     last = pinfo;
+    if (idx++ % GROUP_SIZE != 0)
+      continue;
+    
+    // Create a new group every GROUP_SIZE page infos
+    
+    Page_Info_Group &cur_group = groups[n_groups];
+    cur_group.first = pinfo;
+    cur_group.range.start = pinfo->range.start;
+    if (n_groups > 1) {
+      Page_Info_Group &prev_group = groups[n_groups - 1];
+      prev_group.range.len = cur_group.range.start - prev_group.range.start;
+    }
+
+    assert((!chunks_head) == (n_groups == 0));
+
+    if (!chunks_head) { 
+      assert(!chunks_tail);
+      chunks_head = chunks_tail = arena_push<Page_Info_Chunk>(arena);
+      chunks_head->range.start = cur_group.range.start;
+      chunks_head->first_group = n_groups;
+      ++n_chunks;
+    } else if (groups[n_groups - 1].range.end() != cur_group.range.start) {    
+      // close current chunk
+      Page_Info_Group &prev_group = groups[n_groups - 1];
+      chunks_tail->range.len = (prev_group.range.end() - chunks_tail->range.start);
+      // open new chunk
+      Page_Info_Chunk *chunk = arena_push<Page_Info_Chunk>(arena);
+      chunk->range.start = cur_group.range.start;
+      chunk->first_group = n_groups;
+      chunks_tail->next = chunk;
+      chunks_tail = chunk;
+      ++n_chunks;
+    } else {
+      chunks_tail->range.len += cur_group.range.len;
+    }
+
+    ++n_groups;
   }
   if (last)
     groups[n_groups - 1].range.len = last->range.end() - groups[n_groups - 1].range.start;
diff --git a/src/rntuple.h b/src/rntuple.h
index 7f128ff..46b2b44 100644
--- a/src/rntuple.h
+++ b/src/rntuple.h
@@ -12,7 +12,7 @@ struct Page_Info_Node {
   u64 n_elems;
 };
 
-inline const Page_Info_Node invalid_pinfo = { nullptr, 0, 0 };
+static const Page_Info_Node invalid_pinfo {};
 
 struct Page_Info_Group {
   Byte_Range range;
diff --git a/src/rntviewer.cpp b/src/rntviewer.cpp
index be4f819..d34c396 100644
--- a/src/rntviewer.cpp
+++ b/src/rntviewer.cpp
@@ -121,7 +121,6 @@ int main(int argc, char **argv)
   app.ntpl_name = ntpl_name;
   app.rndata = get_rntuple_data(arena, fname, ntpl_name);
   app.vsettings = make_viewer_settings();
-  app.last_pinfo = &invalid_pinfo;
   
   // Start main loop
   run_main_loop(window, arena, app);