chore(metrics): add rdb_bgsave_in_progress and rdb_last_bgsave_status (#5061)

* add metric rdb_bgsave_in_progress
* add metric rdb_last_bgsave_status

src/server/detail/save_stages_controller.h

@@ -35,6 +35,8 @@ struct SaveStagesInputs {
   Service* service_;
   util::fb2::FiberQueueThreadPool* fq_threadpool_;
   std::shared_ptr<SnapshotStorage> snapshot_storage_;
+  // true if the command that triggered this flow is bgsave. false otherwise.
+  bool is_bg_save_;
 };
 
 class RdbSnapshot {
@@ -77,7 +79,7 @@ class RdbSnapshot {
 };
 
 struct SaveStagesController : public SaveStagesInputs {
-  SaveStagesController(SaveStagesInputs&& input);
+  explicit SaveStagesController(SaveStagesInputs&& input);
   // Objects of this class are used concurrently. Call this function
   // in a mutually exlusive context to avoid data races.
   // Also call this function before any call to `WaitAllSnapshots`
@@ -97,6 +99,10 @@ struct SaveStagesController : public SaveStagesInputs {
   uint32_t GetCurrentSaveDuration();
   RdbSaver::SnapshotStats GetCurrentSnapshotProgress() const;
 
+  bool IsBgSave() const {
+    return is_bg_save_;
+  }
+
  private:
   // In the new version (.dfs) we store a file for every shard and one more summary file.
   // Summary file is always last in snapshots array.
@@ -126,7 +132,6 @@ struct SaveStagesController : public SaveStagesInputs {
 
   void RunStage(void (SaveStagesController::*cb)(unsigned));
 
- private:
   time_t start_time_;
   std::filesystem::path full_path_;
 
@@ -135,6 +140,7 @@ struct SaveStagesController : public SaveStagesInputs {
 
   absl::flat_hash_map<string_view, size_t> rdb_name_map_;
   util::fb2::Mutex rdb_name_map_mu_;
+  bool is_bg_save_ = false;
 };
 
 GenericError ValidateFilename(const std::filesystem::path& filename, bool new_version);

src/server/server_family.cc

@@ -1707,7 +1707,8 @@ GenericError ServerFamily::DoSave(bool ignore_state) {
 }
 
 GenericError ServerFamily::DoSaveCheckAndStart(const SaveCmdOptions& save_cmd_opts,
-                                               Transaction* trans, bool ignore_state) {
+                                               Transaction* trans, DoSaveCheckAndStartOpts opts) {
+  auto [ignore_state, bg_save] = opts;
   auto state = ServerState::tlocal()->gstate();
 
   // In some cases we want to create a snapshot even if server is not active, f.e in takeover
@@ -1728,7 +1729,7 @@ GenericError ServerFamily::DoSaveCheckAndStart(const SaveCmdOptions& save_cmd_op
 
     save_controller_ = make_unique<SaveStagesController>(detail::SaveStagesInputs{
         save_cmd_opts.new_version, save_cmd_opts.cloud_uri, save_cmd_opts.basename, trans,
-        &service_, fq_threadpool_.get(), snapshot_storage});
+        &service_, fq_threadpool_.get(), snapshot_storage, opts.bg_save});
 
     auto res = save_controller_->InitResourcesAndStart();
 
@@ -1736,8 +1737,13 @@ GenericError ServerFamily::DoSaveCheckAndStart(const SaveCmdOptions& save_cmd_op
       DCHECK_EQ(res->error, true);
       last_save_info_.SetLastSaveError(*res);
       save_controller_.reset();
+      if (bg_save) {
+        last_save_info_.last_bgsave_status = false;
+      }
       return res->error;
     }
+
+    last_save_info_.bgsave_in_progress = bg_save;
   }
   return {};
 }
@@ -1751,6 +1757,11 @@ GenericError ServerFamily::WaitUntilSaveFinished(Transaction* trans, bool ignore
     util::fb2::LockGuard lk(save_mu_);
     save_info = save_controller_->Finalize();
 
+    if (save_controller_->IsBgSave()) {
+      last_save_info_.bgsave_in_progress = false;
+      last_save_info_.last_bgsave_status = !save_info.error;
+    }
+
     if (save_info.error) {
       last_save_info_.SetLastSaveError(save_info);
     } else {
@@ -1767,7 +1778,8 @@ GenericError ServerFamily::WaitUntilSaveFinished(Transaction* trans, bool ignore
 
 GenericError ServerFamily::DoSave(const SaveCmdOptions& save_cmd_opts, Transaction* trans,
                                   bool ignore_state) {
-  if (auto ec = DoSaveCheckAndStart(save_cmd_opts, trans, ignore_state); ec) {
+  DoSaveCheckAndStartOpts opts{.ignore_state = ignore_state};
+  if (auto ec = DoSaveCheckAndStart(save_cmd_opts, trans, opts); ec) {
     return ec;
   }
 
@@ -2182,7 +2194,8 @@ void ServerFamily::BgSave(CmdArgList args, const CommandContext& cmd_cntx) {
     return;
   }
 
-  if (auto ec = DoSaveCheckAndStart(*maybe_res, cmd_cntx.tx); ec) {
+  DoSaveCheckAndStartOpts opts{.bg_save = true};
+  if (auto ec = DoSaveCheckAndStart(*maybe_res, cmd_cntx.tx, opts); ec) {
     cmd_cntx.rb->SendError(ec.Format());
     return;
   }
@@ -2621,6 +2634,11 @@ string ServerFamily::FormatInfoMetrics(const Metrics& m, std::string_view sectio
     }
     append("rdb_changes_since_last_success_save", m.events.update);
 
+    auto save = GetLastSaveInfo();
+    append("rdb_bgsave_in_progress", static_cast<int>(save.bgsave_in_progress));
+    std::string val = save.last_bgsave_status ? "ok" : "err";
+    append("rdb_last_bgsave_status", val);
+
     // when last failed save
     append("last_failed_save", save_info.last_error_time);
     append("last_error", save_info.last_error.Format());

src/server/server_family.h

@@ -146,6 +146,9 @@ struct LastSaveInfo {
   GenericError last_error;
   time_t last_error_time = 0;      // epoch time in seconds.
   time_t failed_duration_sec = 0;  // epoch time in seconds.
+  // false if last attempt failed
+  bool last_bgsave_status = true;
+  bool bgsave_in_progress = false;
 };
 
 struct SnapshotSpec {
@@ -340,8 +343,13 @@ class ServerFamily {
 
   void BgSaveFb(boost::intrusive_ptr<Transaction> trans);
 
+  struct DoSaveCheckAndStartOpts {
+    bool ignore_state = false;
+    bool bg_save = false;
+  };
+
   GenericError DoSaveCheckAndStart(const SaveCmdOptions& save_cmd_opts, Transaction* trans,
-                                   bool ignore_state = false) ABSL_LOCKS_EXCLUDED(save_mu_);
+                                   DoSaveCheckAndStartOpts opts) ABSL_LOCKS_EXCLUDED(save_mu_);
 
   GenericError WaitUntilSaveFinished(Transaction* trans,
                                      bool ignore_state = false) ABSL_NO_THREAD_SAFETY_ANALYSIS;