feat(update_replication_factor#7): replace cluster-level max_replicas…

…_in_group with max_replica_count of each replica

src/meta/meta_data.cpp

@@ -36,12 +36,19 @@
 
 #include <dsn/dist/fmt_logging.h>
 #include <dsn/service_api_cpp.h>
+#include <dsn/utility/flags.h>
 
 #include "meta_data.h"
 
 namespace dsn {
 namespace replication {
 
+DSN_DEFINE_uint32("meta_server",
+ max_reserved_number_of_dropped_replicas,
+ 1,
+ "max reserved number allowed for dropped replicas");
+DSN_TAG_VARIABLE(max_reserved_number_of_dropped_replicas, FT_MUTABLE);
+
 void when_update_replicas(config_type::type t, const std::function<void(bool)> &func)
 {
  switch (t) {
@@ -301,7 +308,8 @@ void config_context::check_size()
 {
  // when add learner, it is possible that replica_count > max_replica_count, so we
  // need to remove things from dropped only when it's not empty.
- while (replica_count(*config_owner) + dropped.size() > MAX_REPLICA_COUNT_IN_GRROUP &&
+ while (replica_count(*config_owner) + dropped.size() >
+ config_owner->max_replica_count + FLAGS_max_reserved_number_of_dropped_replicas &&
  !dropped.empty()) {
  dropped.erase(dropped.begin());
  prefered_dropped = (int)dropped.size() - 1;