diff --git a/td/telegram/Global.cpp b/td/telegram/Global.cpp
index 2fbfa7d6..3ccb0ec2 100644
--- a/td/telegram/Global.cpp
+++ b/td/telegram/Global.cpp
@@ -71,14 +71,30 @@ Status Global::init(const TdParameters &parameters, ActorId<Td> td, unique_ptr<T
   td_db_ = std::move(td_db_ptr);
 
   string save_diff_str = td_db()->get_binlog_pmc()->get("server_time_difference");
-  auto default_time_difference = Clocks::system() - Time::now();
+  string save_system_time_str = td_db()->get_binlog_pmc()->get("system_time");
+  auto system_time = Clocks::system();
+  auto default_time_difference = system_time - Time::now();
   if (save_diff_str.empty()) {
     server_time_difference_ = default_time_difference;
     server_time_difference_was_updated_ = false;
   } else {
     double save_diff;
     unserialize(save_diff, save_diff_str).ensure();
+
+    double save_system_time;
+    if (save_system_time_str.empty()) {
+      save_system_time = 0;
+    } else {
+      unserialize(save_system_time, save_system_time_str).ensure();
+    }
+
     double diff = save_diff + default_time_difference;
+    if (save_system_time > system_time) {
+      double time_backwards_fix = save_system_time - system_time;
+      LOG(WARNING) << "Fix system time which went backwards: " << format::as_time(time_backwards_fix) << " "
+                   << tag("saved_system_time", save_system_time) << tag("system_time", system_time);
+      diff += time_backwards_fix;
+    }
     LOG(DEBUG) << "LOAD: " << tag("server_time_difference", diff);
     server_time_difference_ = diff;
     server_time_difference_was_updated_ = false;
@@ -97,8 +113,19 @@ void Global::update_server_time_difference(double diff) {
     // diff = server_time - Time::now
     // save_diff = server_time - Clocks::system
     double save_diff = diff + Time::now() - Clocks::system();
-    auto str = serialize(save_diff);
-    td_db()->get_binlog_pmc()->set("server_time_difference", str);
+
+    td_db()->get_binlog_pmc()->set("server_time_difference", serialize(save_diff));
+    save_system_time();
+  }
+}
+
+void Global::save_system_time() {
+  auto t = Time::now();
+  if (system_time_saved_at_.load(std::memory_order_relaxed) + 10 < t) {
+    system_time_saved_at_ = t;
+    double save_system_time = Clocks::system();
+    LOG(INFO) << "Save system time";
+    td_db()->get_binlog_pmc()->set("system_time", serialize(save_system_time));
   }
 }
 
diff --git a/td/telegram/Global.h b/td/telegram/Global.h
index a70b592c..93007f77 100644
--- a/td/telegram/Global.h
+++ b/td/telegram/Global.h
@@ -144,6 +144,7 @@ class Global : public ActorContext {
   }
 
   void update_server_time_difference(double diff);
+  void save_system_time();
 
   double get_server_time_difference() const {
     return server_time_difference_.load(std::memory_order_relaxed);
@@ -407,6 +408,7 @@ class Global : public ActorContext {
   std::atomic<double> dns_time_difference_{0.0};
   std::atomic<bool> dns_time_difference_was_updated_{false};
   std::atomic<bool> close_flag_{false};
+  std::atomic<double> system_time_saved_at_{0.0};
 
   std::vector<std::shared_ptr<NetStatsCallback>> net_stats_file_callbacks_;
 
diff --git a/td/telegram/files/FileManager.cpp b/td/telegram/files/FileManager.cpp
index d7857247..25f5132f 100644
--- a/td/telegram/files/FileManager.cpp
+++ b/td/telegram/files/FileManager.cpp
@@ -42,6 +42,7 @@
 #include <algorithm>
 #include <cmath>
 #include <limits>
+#include <numeric>
 #include <tuple>
 #include <utility>
 
@@ -1384,6 +1385,12 @@ Result<FileId> FileManager::merge(FileId x_file_id, FileId y_file_id, bool no_sy
     LOG(WARNING) << "File remote location was changed from " << y_node->remote_.full.value() << " to "
                  << x_node->remote_.full.value();
   }
+  auto count_local = [](auto &node) {
+    return std::accumulate(node->file_ids_.begin(), node->file_ids_.end(), 0,
+                           [](const auto &x, const auto &y) { return x + (y.get_remote() != 0); });
+  };
+  if (count_local(x_node) + count_local(y_node) > 100) {
+  }
 
   FileNodePtr nodes[] = {x_node, y_node, x_node};
   FileNodeId node_ids[] = {get_file_id_info(x_file_id)->node_id_, get_file_id_info(y_file_id)->node_id_};
diff --git a/td/telegram/net/ConnectionCreator.cpp b/td/telegram/net/ConnectionCreator.cpp
index 040a663e..8ae9e583 100644
--- a/td/telegram/net/ConnectionCreator.cpp
+++ b/td/telegram/net/ConnectionCreator.cpp
@@ -577,6 +577,7 @@ void ConnectionCreator::on_online(bool online_flag) {
 }
 
 void ConnectionCreator::on_pong(size_t hash) {
+  G()->save_system_time();
   if (active_proxy_id_ != 0) {
     auto now = G()->unix_time();
     int32 &last_used = proxy_last_used_date_[active_proxy_id_];
@@ -1006,6 +1007,7 @@ void ConnectionCreator::client_add_connection(size_t hash, Result<unique_ptr<mtp
 
 void ConnectionCreator::client_wakeup(size_t hash) {
   LOG(INFO) << tag("hash", format::as_hex(hash)) << " wakeup";
+  G()->save_system_time();
   client_loop(clients_[hash]);
 }
 
diff --git a/td/telegram/net/Session.cpp b/td/telegram/net/Session.cpp
index 8fb4a542..455a4798 100644
--- a/td/telegram/net/Session.cpp
+++ b/td/telegram/net/Session.cpp
@@ -119,7 +119,7 @@ Session::Session(unique_ptr<Callback> callback, std::shared_ptr<AuthDataShared>
                  int32 dc_id, bool is_main, bool use_pfs, bool is_cdn, bool need_destroy,
                  const mtproto::AuthKey &tmp_auth_key, std::vector<mtproto::ServerSalt> server_salts)
     : raw_dc_id_(raw_dc_id), dc_id_(dc_id), is_main_(is_main), is_cdn_(is_cdn) {
-  VLOG(dc) << "Start connection";
+  VLOG(dc) << "Start connection " << tag("need_destroy", need_destroy);
   need_destroy_ = need_destroy;
   if (need_destroy) {
     use_pfs = false;