feat(remote_command): allow empty writes to be queried/enabled/disabl…

…ed by remote command (#2153)

Support querying/enabling/disabling empty writes on one, multiple or all replica servers
by just one remote command conveniently.

For example, after a table is migrated from a cluster A to another cluster B by duplication,
we want to check whether that migration has been finished by decree. However, since
empty writes would increase the decree, it is necessary to use only one command to
disable empty writes on all replica servers of cluster A without need to restart all of them.

src/replica/replica_stub.cpp

@@ -229,6 +229,7 @@ METRIC_DEFINE_gauge_int64(server,
                           "The max size of copied files among all splitting replicas");
 
 DSN_DECLARE_bool(duplication_enabled);
+DSN_DECLARE_bool(empty_write_disabled);
 DSN_DECLARE_bool(enable_acl);
 DSN_DECLARE_bool(encrypt_data_at_rest);
 DSN_DECLARE_int32(fd_beacon_interval_seconds);
@@ -2354,6 +2355,11 @@ void replica_stub::register_ctrl_command()
                 });
             }));
 
+        _cmds.emplace_back(::dsn::command_manager::instance().register_bool_command(
+            FLAGS_empty_write_disabled,
+            "replica.disable-empty-write",
+            "whether to disable empty writes"));
+
 #ifdef DSN_ENABLE_GPERF
         _cmds.emplace_back(::dsn::command_manager::instance().register_bool_command(
             _release_tcmalloc_memory,