[SKV-636] refactor: remove useless function 'last_flushed_decree()' (a…

…pache#1456)

对应社区commit: https://github.com/apache/incubator-pegasus/pull/1456/files

apache#1383

This is a refactor patch before fixing apache#1383. This patch has no functionality
changes, but just including refactors:
1. Moves functions `load()`, `newr()` and `clear_on_failure()` from class replica
to class replica_stub, and the first two have been renamed to `load_replica()`
and `new_replica()`.
2. Encapsulates a new function `move_to_err_path`.
3. Some minor refactors like fix typo.

src/rdsn/include/dsn/dist/replication/replication_app_base.h

@@ -210,7 +210,6 @@ class replication_app_base : public replica_base
     // Query methods.
     //
     virtual replication::decree last_durable_decree() const = 0;
-    virtual replication::decree last_flushed_decree() const { return last_durable_decree(); }
     // The return type is generated by storage engine, e.g. rocksdb::Status::Code, 0 always mean OK.
     virtual int on_request(message_ex *request) = 0;
 

src/rdsn/src/replica/replica.cpp

@@ -418,8 +418,6 @@ mutation_ptr replica::new_mutation(decree decree)
 
 decree replica::last_durable_decree() const { return _app->last_durable_decree(); }
 
-decree replica::last_flushed_decree() const { return _app->last_flushed_decree(); }
-
 decree replica::last_prepared_decree() const
 {
     ballot lastBallot = 0;

src/rdsn/src/replica/replica.h

@@ -197,7 +197,6 @@ class replica : public serverlet<replica>, public ref_counter, public replica_ba
     decree last_committed_decree() const { return _prepare_list->last_committed_decree(); }
     decree last_prepared_decree() const;
     decree last_durable_decree() const;
-    decree last_flushed_decree() const;
     const std::string &dir() const { return _dir; }
     uint64_t create_time_milliseconds() const { return _create_time_ms; }
     const char *name() const { return replica_name(); }

src/server/pegasus_server_impl.cpp

@@ -2597,11 +2597,6 @@ void pegasus_server_impl::update_app_envs(const std::map<std::string, std::strin
     update_throttling_controller(envs);
 }
 
-int64_t pegasus_server_impl::last_flushed_decree() const
-{
-    return _meta_store->get_last_flushed_decree();
-}
-
 void pegasus_server_impl::update_app_envs_before_open_db(
     const std::map<std::string, std::string> &envs)
 {
@@ -3174,7 +3169,7 @@ bool pegasus_server_impl::release_storage_after_manual_compact()
     gc_checkpoints(true);
     ddebug_replica("finish gc_checkpoints, time_used = {}ms", dsn_now_ms() - start_time);
 
-    int64_t new_last_durable = last_flushed_decree();
+    int64_t new_last_durable = _meta_store->get_last_flushed_decree();
     if (new_last_durable > old_last_durable) {
         ddebug_replica("release storage succeed, last_durable_decree changed from {} to {}",
                        old_last_durable,

src/server/pegasus_server_impl.h

@@ -181,8 +181,6 @@ class pegasus_server_impl : public pegasus_read_service
 
     int64_t last_durable_decree() const override { return _last_durable_decree.load(); }
 
-    int64_t last_flushed_decree() const override;
-
     void update_app_envs(const std::map<std::string, std::string> &envs) override;
 
     void query_app_envs(/*out*/ std::map<std::string, std::string> &envs) override;