diff --git a/src/app_state.h b/src/app_state.h
index d194b45..48e5383 100644
--- a/src/app_state.h
+++ b/src/app_state.h
@@ -16,13 +16,18 @@ struct Inspected_File {
   int inot;
 };
 
-struct App_State {
-  u8 should_quit;
-  
-  Window_Data win_data;
-  User_Input user_input;
+// These data gets dropped and regenerated every time the file changes
+struct Loaded_File_Data {
   RNTuple_Data rndata;
   TFile_Data tfile_data;
+};
+
+struct App_State {
+  b8 should_quit;
+  
+  Loaded_File_Data *fdata;
+  Window_Data win_data;
+  User_Input user_input;
   Inspected_File inspected_file;
 
 #ifndef RNT_NO_GFX
@@ -34,9 +39,14 @@ struct App_State {
 
   Delta_Time_Accum delta_time_accum;
 
-  // Cache the last info node selected for faster lookup of offsets
+  // Cache the last info node selected for faster lookup of offsets.
+  // These are reset every frame.
   const Page_Info_Node *last_pinfo;
   const Section *last_other_root_obj;
+
+  // Saved command line args that are used when hot-reloading the file.
+  u32 walk_tkeys_flags;
+  b8 extended_info;
 };
 
 internal
diff --git a/src/mainloop.cpp b/src/mainloop.cpp
index a47e930..2b8c48a 100644
--- a/src/mainloop.cpp
+++ b/src/mainloop.cpp
@@ -157,8 +157,15 @@ void run_main_loop(GLFWwindow *window, Arena *arena, App_State &app)
       // TODO: this should re-run get_tfile_data and get_rntuple_data!
       char buf[sizeof(inotify_event) + NAME_MAX + 1];
       ssize_t nbytes = read(app.inspected_file.inot, buf, sizeof(buf));
-      if (nbytes)
-        app.inspected_file.size = file_size(app.inspected_file.stream);    
+      if (nbytes > 0) {
+        printf("nbytes %ld\n", nbytes);
+        app.inspected_file.size = file_size(app.inspected_file.stream);
+        // @Leak! Use two arenas?
+        b8 success = get_tfile_data(arena, app.inspected_file, app.walk_tkeys_flags, app.ntpl_name, app.fdata->tfile_data);
+        if (success)
+          app.fdata->rndata = get_rntuple_data(arena, app.inspected_file, app.fdata->tfile_data, app.extended_info);
+        compute_tot_sections_size(app.fdata->tfile_data.sections);
+      }
     }
 
     if ((app.user_input.key_state[KEY_ESC] & KEY_STATE_IS_DOWN) || glfwWindowShouldClose(window)) {
diff --git a/src/render.cpp b/src/render.cpp
index 7d0d13b..68923a4 100644
--- a/src/render.cpp
+++ b/src/render.cpp
@@ -141,15 +141,17 @@ void init_viewer(Arena *arena, App_State &app, u16 n_cols)
 {
   Viewer &viewer = app.viewer;
   viewer.mem_edit = make_memory_editor(app, (i32)n_cols);
+
+  const TFile_Data &tfile_data = app.fdata->tfile_data;
   
   // Init title
-  u32 n_ntuples = app.tfile_data.sections[Sec_RNTuple_Anchor].count;
+  u32 n_ntuples = tfile_data.sections[Sec_RNTuple_Anchor].count;
   if (n_ntuples) {
     Temp scratch = scratch_begin(&arena, 1);
     defer { scratch_end(scratch); };
 
     if (n_ntuples == 1) {
-      Section *sec = app.tfile_data.sections[Sec_RNTuple_Anchor].head;
+      Section *sec = tfile_data.sections[Sec_RNTuple_Anchor].head;
       const RNTuple_Anchor_Info *anchor = (const RNTuple_Anchor_Info *)sec->info;
       String8 ntpl_desc = rntuple_description(scratch.arena, anchor->anchor);
       if (rntuple_is_old_version(anchor->anchor)) {
@@ -163,7 +165,7 @@ void init_viewer(Arena *arena, App_State &app, u16 n_cols)
       }
     } else {
       String8 title = str8("RNTuples");
-      for (Section *sec = app.tfile_data.sections[Sec_RNTuple_Anchor].head; sec; sec = sec->next) {
+      for (Section *sec = tfile_data.sections[Sec_RNTuple_Anchor].head; sec; sec = sec->next) {
         const RNTuple_Anchor_Info *anchor = (const RNTuple_Anchor_Info *)sec->info;
         String8 s = push_str8f(scratch.arena, " \"%s;%hu\",", anchor->name, anchor->cycle);
         title = str8_concat(scratch.arena, title, s);
@@ -210,13 +212,13 @@ void viewer_jump_to(App_State &app, u64 addr)
 internal
 Page_Info_Node *viewer_jump_to_page(App_State &app, u64 page_idx)
 {
-  if (app.rndata.n_pages == 0)
+  if (app.fdata->rndata.n_pages == 0)
     return nullptr;
-  page_idx = (page_idx + app.rndata.n_pages) % app.rndata.n_pages;
+  page_idx = (page_idx + app.fdata->rndata.n_pages) % app.fdata->rndata.n_pages;
   
   #if 1
   // @Speed
-  Page_Info_Node *page = app.rndata.pages;
+  Page_Info_Node *page = app.fdata->rndata.pages;
   for (u64 i = 0; i < page_idx; ++i) {
     page = page->next;    
     assert(page);
@@ -226,9 +228,9 @@ Page_Info_Node *viewer_jump_to_page(App_State &app, u64 page_idx)
   // Find the page_idx-th page. We could just iterate n times over the pages list,
   // but skimming through the clusters first should be faster in most cases.
   Page_Info_Node *page = nullptr;
-  for (u64 i = 0; i < app.rndata.n_clusters - 1; ++i) {
-    const Cluster_Info &cluster = app.rndata.clusters[i];
-    const Cluster_Info &next_cluster = app.rndata.clusters[i];
+  for (u64 i = 0; i < app.fdata->rndata.n_clusters - 1; ++i) {
+    const Cluster_Info &cluster = app.fdata->rndata.clusters[i];
+    const Cluster_Info &next_cluster = app.fdata->rndata.clusters[i];
     if (cluster.first_page_idx <= page_idx && page_idx < next_cluster.first_page_idx) {
       u64 idx_in_cluster = page_idx - cluster.first_page_idx;
       page = cluster.first_page; 
@@ -240,7 +242,7 @@ Page_Info_Node *viewer_jump_to_page(App_State &app, u64 page_idx)
   }
   if (!page) {
     // page was not in the first N - 1 clusters, so it must be in the last one.
-    const Cluster_Info &cluster = app.rndata.clusters[app.rndata.n_clusters - 1];
+    const Cluster_Info &cluster = app.fdata->rndata.clusters[app.fdata->rndata.n_clusters - 1];
     assert(page_idx >= cluster.first_page_idx);
     u64 idx_in_cluster = page_idx - cluster.first_page_idx;
     page = cluster.first_page; 
@@ -259,11 +261,11 @@ Page_Info_Node *viewer_jump_to_page(App_State &app, u64 page_idx)
 internal
 void viewer_jump_to_cluster(App_State &app, u64 cluster_idx)
 {
-  if (app.rndata.n_clusters == 0)
+  if (app.fdata->rndata.n_clusters == 0)
     return;
-  cluster_idx = (cluster_idx + app.rndata.n_clusters) % app.rndata.n_clusters;
+  cluster_idx = (cluster_idx + app.fdata->rndata.n_clusters) % app.fdata->rndata.n_clusters;
   
-  Cluster_Info &cluster = app.rndata.clusters[cluster_idx];
+  Cluster_Info &cluster = app.fdata->rndata.clusters[cluster_idx];
   Page_Info_Node *page = cluster.first_page;
   assert(page);
 
@@ -275,12 +277,12 @@ void viewer_jump_to_cluster(App_State &app, u64 cluster_idx)
 internal
 void viewer_jump_to_page_list(App_State &app, u64 page_list_idx)
 {
-  if (app.rndata.n_cluster_groups == 0)
+  if (app.fdata->rndata.n_cluster_groups == 0)
     return;
 
-  page_list_idx = (page_list_idx + app.rndata.n_cluster_groups) % app.rndata.n_cluster_groups;
+  page_list_idx = (page_list_idx + app.fdata->rndata.n_cluster_groups) % app.fdata->rndata.n_cluster_groups;
 
-  Cluster_Group_Info &cg_info = app.rndata.cluster_groups[page_list_idx];
+  Cluster_Group_Info &cg_info = app.fdata->rndata.cluster_groups[page_list_idx];
 
   app.viewer.latest_section_gone_to[Sec_Page_List] = page_list_idx;
   viewer_jump_to(app, cg_info.rng_page_list.start);
@@ -295,7 +297,7 @@ void viewer_jump_to_section(App_State &app, Section_Id id, u64 &sec_idx)
     return;
   }
   
-  const Sections &sections = app.tfile_data.sections[id];
+  const Sections &sections = app.fdata->tfile_data.sections[id];
   if (sections.count == 0)
     return;
   
@@ -414,7 +416,7 @@ void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
 
       // Unique sections: just display a button that jumps to the start of it and show their size
       for (u32 i = 1; i < Sec_COUNT; ++i) {
-        if (!app.tfile_data.sections[i].head)
+        if (!app.fdata->tfile_data.sections[i].head)
           continue;
 
         // TODO: handle pages like other sections
@@ -429,10 +431,10 @@ void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
           viewer_jump_to_section(app, static_cast<Section_Id>(i), app.viewer.latest_section_gone_to[i]);
         ImGui::SameLine(); 
 
-        ImGui::Text("%s", to_pretty_size(scratch.arena, app.tfile_data.sections[i].tot_size).c());
-        if (app.tfile_data.sections[i].count > 1) {
+        ImGui::Text("%s", to_pretty_size(scratch.arena, app.fdata->tfile_data.sections[i].tot_size).c());
+        if (app.fdata->tfile_data.sections[i].count > 1) {
         // } else {
-        //   ImGui::Text("%s (%u)", to_pretty_size(scratch.arena, app.tfile_data.sections[i].tot_size).c(), app.tfile_data.sections[i].count);
+        //   ImGui::Text("%s (%u)", to_pretty_size(scratch.arena, app.fdata->tfile_data.sections[i].tot_size).c(), app.fdata->tfile_data.sections[i].count);
           ImGui::SameLine(); 
           i64 sec_to_go_to = app.viewer.latest_section_gone_to[i];
           ImGui::PushItemWidth(120.f);
@@ -445,7 +447,7 @@ void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
           }
           ImGui::PopItemWidth();
           ImGui::SameLine();
-          ImGui::Text(" / %u", app.tfile_data.sections[i].count);
+          ImGui::Text(" / %u", app.fdata->tfile_data.sections[i].count);
         }
       }
 
@@ -454,7 +456,7 @@ void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
       ImGui::SameLine(); 
       if (ImGui::Button("TKey Header")) {} // TODO: jump to next key
 
-      if (app.rndata.n_pages) {
+      if (app.fdata->rndata.n_pages) {
         ImGui::ColorEdit3("_Page Start", app.viewer.col_page_start, edit_flags);
         ImGui::SameLine(); 
         if (ImGui::Button("Page Start"))
@@ -466,7 +468,7 @@ void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
           app.viewer.latest_page = viewer_jump_to_page(app, app.viewer.latest_section_gone_to[Sec_Page]);
         ImGui::SameLine();
         {
-          const i64 step_fast_i64 = app.rndata.n_pages / 100;
+          const i64 step_fast_i64 = app.fdata->rndata.n_pages / 100;
           i64 page_to_go_to = app.viewer.latest_section_gone_to[Sec_Page];
           ImGui::PushItemWidth(100.f);
           if (ImGui::InputScalar("##page_viewed", ImGuiDataType_S64, &page_to_go_to, &step_i64, &step_fast_i64, "%u") && 
@@ -479,9 +481,9 @@ void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
         ImGui::SameLine();
         String8 this_page_width = app.viewer.latest_page 
                                   ? push_str8f(scratch.arena, " / %" PRIu64 " (this page: %s)", 
-                                               app.rndata.n_pages, to_pretty_size(scratch.arena, app.viewer.latest_page->range.len).c()) 
+                                               app.fdata->rndata.n_pages, to_pretty_size(scratch.arena, app.viewer.latest_page->range.len).c()) 
                                   : str8("");
-        ImGui::Text("%s%s", to_pretty_size(scratch.arena, app.rndata.tot_page_comp_size).c(), this_page_width.c());
+        ImGui::Text("%s%s", to_pretty_size(scratch.arena, app.fdata->rndata.tot_page_comp_size).c(), this_page_width.c());
       }
 
       ImGui::ColorEdit3("_Checksum", app.viewer.col_checksum, edit_flags);
@@ -492,22 +494,22 @@ void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
       // -------------------------------
       ImGui::Separator();
       String8 root_version_str = push_str8f(scratch.arena, "%u.%u.%u", 
-                                            app.tfile_data.root_version_major,
-                                            app.tfile_data.root_version_minor,
-                                            app.tfile_data.root_version_patch);
+                                            app.fdata->tfile_data.root_version_major,
+                                            app.fdata->tfile_data.root_version_minor,
+                                            app.fdata->tfile_data.root_version_patch);
       ImGui::Text("ROOT version: %s", root_version_str.c());
-      ImGui::Text("TFile compression: %u", app.tfile_data.compression);
-      ImGui::Text("Num pages: %lu", app.rndata.n_pages);
-      ImGui::Text("Num elements: %lu", app.rndata.n_elems);
-      ImGui::Text("Num entries: %lu", app.rndata.n_entries);
-      if (app.rndata.tot_page_uncomp_size) {
+      ImGui::Text("TFile compression: %u", app.fdata->tfile_data.compression);
+      ImGui::Text("Num pages: %lu", app.fdata->rndata.n_pages);
+      ImGui::Text("Num elements: %lu", app.fdata->rndata.n_elems);
+      ImGui::Text("Num entries: %lu", app.fdata->rndata.n_entries);
+      if (app.fdata->rndata.tot_page_uncomp_size) {
         ImGui::Text("Pages uncompr. size: %s (comp.ratio = %.3f)",
-                    to_pretty_size(scratch.arena, app.rndata.tot_page_uncomp_size).c(),
-                    (f32)app.rndata.tot_page_comp_size / app.rndata.tot_page_uncomp_size);
+                    to_pretty_size(scratch.arena, app.fdata->rndata.tot_page_uncomp_size).c(),
+                    (f32)app.fdata->rndata.tot_page_comp_size / app.fdata->rndata.tot_page_uncomp_size);
       }
 
       {
-        const i64 step_fast_i64 = app.rndata.n_clusters / 100;
+        const i64 step_fast_i64 = app.fdata->rndata.n_clusters / 100;
         i64 cluster_to_highlight = app.viewer.highlighted_cluster;
         ImGui::PushItemWidth(100.f);
         if (ImGui::InputScalar("##highlighted_cluster", ImGuiDataType_S64, &cluster_to_highlight, &step_i64, &step_fast_i64, "%u") &&
diff --git a/src/render_term.cpp b/src/render_term.cpp
index 4b52c2a..152de6d 100644
--- a/src/render_term.cpp
+++ b/src/render_term.cpp
@@ -55,12 +55,12 @@ String8_Node *render_legend_to_string(Arena *arena, const Term_Viewer &viewer, c
                    range.start, range.end(), to_pretty_size(arena, range.len).c());
     else if (section == Sec_Page)
       tail = push_str8_node(arena, tail, "%s%20s %s(%lu) [%s] \n", 
-                   color_str.c(), sec_name.c(), color_none.c(), app.rndata.n_pages,
-                   to_pretty_size(arena, app.rndata.tot_page_comp_size).c());
+                   color_str.c(), sec_name.c(), color_none.c(), app.fdata->rndata.n_pages,
+                   to_pretty_size(arena, app.fdata->rndata.tot_page_comp_size).c());
     else if (section == Sec_Page_List)
       tail = push_str8_node(arena, tail, "%s%20s %s(%lu) [%s]\n", 
-                   color_str.c(), sec_name.c(), color_none.c(), app.rndata.n_cluster_groups, 
-                   to_pretty_size(arena, app.rndata.tot_page_list_size).c());
+                   color_str.c(), sec_name.c(), color_none.c(), app.fdata->rndata.n_cluster_groups, 
+                   to_pretty_size(arena, app.fdata->rndata.tot_page_list_size).c());
     if (!head) {
       head = tail;
       if (prev)
@@ -87,15 +87,15 @@ String8_Node *render_info_to_string(Arena *arena, Byte_Range range, const App_St
     "  Num elements: %lu\n",
     ansi_color_table[ACol_None].c(),
     range.start, range.end(), app.inspected_file.size,
-    app.tfile_data.root_version_major, app.tfile_data.root_version_minor, app.tfile_data.root_version_patch,
-    app.tfile_data.compression,
-    app.rndata.n_pages,
-    app.rndata.n_elems);
+    app.fdata->tfile_data.root_version_major, app.fdata->tfile_data.root_version_minor, app.fdata->tfile_data.root_version_patch,
+    app.fdata->tfile_data.compression,
+    app.fdata->rndata.n_pages,
+    app.fdata->rndata.n_elems);
 
-  if (app.rndata.tot_page_uncomp_size) {
+  if (app.fdata->rndata.tot_page_uncomp_size) {
     res = push_str8_node(arena, res, "  Pages uncompressed size: %s (comp.ratio = %.3f)\n",
-                         to_pretty_size(arena, app.rndata.tot_page_uncomp_size).c(),
-                         (f32)app.rndata.tot_page_comp_size / app.rndata.tot_page_uncomp_size);
+                         to_pretty_size(arena, app.fdata->rndata.tot_page_uncomp_size).c(),
+                         (f32)app.fdata->rndata.tot_page_comp_size / app.fdata->rndata.tot_page_uncomp_size);
   }
 
   return res;
@@ -217,7 +217,9 @@ String8_Node *render_range_to_string(Arena *arena, App_State &app, u64 len, u64
   defer { scratch_end(scratch); };
 
   // Header
-  String8 ntpl_desc = rntuple_description(scratch.arena, ((const RNTuple_Anchor_Info *)app.tfile_data.sections[Sec_RNTuple_Anchor].head->info)->anchor); // FIXME :multiple_anchors:
+  // FIXME :multiple_anchors:
+  String8 ntpl_desc = rntuple_description(scratch.arena,
+                                          ((const RNTuple_Anchor_Info *)app.fdata->tfile_data.sections[Sec_RNTuple_Anchor].head->info)->anchor); 
   String8_Node *result = push_str8_node(arena, nullptr, "RNTuple '%s' (%s) from file \"%s\"\n",
                                         app.ntpl_name.c(), ntpl_desc.c(), app.inspected_file.name.c());
   String8_Node *result_tail = result;
diff --git a/src/rntuple.cpp b/src/rntuple.cpp
index dab63f2..7f68dcf 100644
--- a/src/rntuple.cpp
+++ b/src/rntuple.cpp
@@ -485,12 +485,13 @@ Section find_section(App_State &app, u64 off, i64 hilite_cluster = -1)
   // These are supposed to never be null. If they are invalid, they must be set to `&invalid_pinfo` etc.
   assert(app.last_pinfo);
   
-  const RNTuple_Data &rdata = app.rndata;
+  const RNTuple_Data &rdata = app.fdata->rndata;
+  const TFile_Data &tfile_data = app.fdata->tfile_data;
 
   Section sec {};
 
   for (u32 i = 1; i < Sec_COUNT_Regular; ++i) {   
-    for (Section *sec = app.tfile_data.sections[i].head; sec; sec = sec->next) {
+    for (Section *sec = tfile_data.sections[i].head; sec; sec = sec->next) {
       if (sec->range.start - sec->pre_size <= off && off < sec->range.end()) {
         return *sec;
       }
@@ -499,8 +500,8 @@ Section find_section(App_State &app, u64 off, i64 hilite_cluster = -1)
 
   // Page / PageList lookup.
   // If we don't have a Sec_Page section it means we don't have any RNTuple, so skip it.
-  if (app.tfile_data.sections[Sec_Page].head) {
-    u64 rblob_sz = app.tfile_data.sections[Sec_Page].head->pre_size;
+  if (tfile_data.sections[Sec_Page].head) {
+    u64 rblob_sz = tfile_data.sections[Sec_Page].head->pre_size;
 
     /// Page fast lookup (relative to app.last_pinfo)
     {
@@ -578,7 +579,7 @@ Section find_section(App_State &app, u64 off, i64 hilite_cluster = -1)
 
   // Lookup other root objects.
   // @Copypasted from the fast page lookup
-  if (app.tfile_data.sections[Sec_Other].count > 0) {
+  if (tfile_data.sections[Sec_Other].count > 0) {
     // fast case: `off` is in the same obj as previous `off`.
     for (i32 i = 0; i < 2; ++i) {
       const Section &other_sec = *app.last_other_root_obj;
@@ -594,7 +595,7 @@ Section find_section(App_State &app, u64 off, i64 hilite_cluster = -1)
     }
 
     // Slow linear lookup, ideally only done once per render when last_other_root_obj is invalid.
-    for (Section *other_sec = app.tfile_data.sections[Sec_Other].head; other_sec; other_sec = other_sec->next) {
+    for (Section *other_sec = tfile_data.sections[Sec_Other].head; other_sec; other_sec = other_sec->next) {
       if (other_sec->range.start - other_sec->pre_size <= off && off < other_sec->range.end()) {
         app.last_other_root_obj = other_sec;
         return *other_sec;
diff --git a/src/rntviewer.cpp b/src/rntviewer.cpp
index 61d8fbb..873363f 100644
--- a/src/rntviewer.cpp
+++ b/src/rntviewer.cpp
@@ -164,9 +164,13 @@ int main(int argc, char **argv)
     walk_tkeys_flags |= WTK_PRINT_KEYS_INFO;
   if (!args.dont_collect_other_root_objs)
     walk_tkeys_flags |= WTK_COLLECT_OTHER_ROOT_OBJS;
-  b8 success = get_tfile_data(arena, app.inspected_file, walk_tkeys_flags, app.ntpl_name, app.tfile_data);
+  app.walk_tkeys_flags = walk_tkeys_flags;
+  app.extended_info = args.extended_info;
+
+  app.fdata = arena_push<Loaded_File_Data>(arena);
+  b8 success = get_tfile_data(arena, app.inspected_file, walk_tkeys_flags, app.ntpl_name, app.fdata->tfile_data);
   if (args.only_print_rntuple_names) {
-    for (Section *sec = app.tfile_data.sections[Sec_RNTuple_Anchor].head; sec; sec = sec->next) {
+    for (Section *sec = app.fdata->tfile_data.sections[Sec_RNTuple_Anchor].head; sec; sec = sec->next) {
       const RNTuple_Anchor_Info *info = (const RNTuple_Anchor_Info *)sec->info;
       printf("%s at 0x%" PRIX64 "\n", info->name.c(), info->offset_in_file);
     }
@@ -174,9 +178,9 @@ int main(int argc, char **argv)
   }
 
   if (success)
-    app.rndata = get_rntuple_data(arena, app.inspected_file, app.tfile_data, args.extended_info);
+    app.fdata->rndata = get_rntuple_data(arena, app.inspected_file, app.fdata->tfile_data, args.extended_info);
 
-  compute_tot_sections_size(app.tfile_data.sections);
+  compute_tot_sections_size(app.fdata->tfile_data.sections);
 
   if (args.print_to_terminal) {
     u64 nbytes_displayed = args.nbytes_displayed;