25-3-1: make storage balancer async (#29212)

Author: vporyadke

ydb/core/mind/hive/hive_ut.cpp

@@ -3392,6 +3392,8 @@ Y_UNIT_TEST_SUITE(THiveTest) {
         const ui64 testerTablet = MakeTabletID(false, 1);
         CreateTestBootstrapper(runtime, CreateTestTabletInfo(hiveTablet, TTabletTypes::Hive), &CreateDefaultHive);
 
+        auto syncReassign = runtime.AddObserver<TEvHive::TEvReassignTablet>([] (auto&& ev) { ev->Get()->Record.SetAsync(false); });
+
         TTabletTypes::EType tabletType = TTabletTypes::Dummy;
         TVector<ui64> tablets;
         for (ui64 i = 0; i < NUM_TABLETS; ++i) {
@@ -9075,6 +9077,11 @@ Y_UNIT_TEST_SUITE(TStorageBalanceTest) {
                         OnBootTablet(info);
                         return TTestActorRuntime::EEventAction::PROCESS;
                     }
+                    case TEvHive::EvReassignTablet: {
+                        auto& record = ev->Get<TEvHive::TEvReassignTablet>()->Record;
+                        record.SetAsync(false);
+                        return TTestActorRuntime::EEventAction::PROCESS;
+                    }
                 }
                 return TTestActorRuntime::EEventAction::PROCESS;
             };

ydb/core/mind/hive/storage_balancer.cpp

@@ -177,6 +177,7 @@ class THiveStorageBalancer : public NActors::TActorBootstrapped<THiveStorageBala
             if (!ev) {
                 ev = std::make_unique<TEvHive::TEvReassignTablet>(channel.TabletId);
                 ev->Record.SetReassignReason(NKikimrHive::TEvReassignTablet::HIVE_REASSIGN_REASON_BALANCE);
+                ev->Record.SetAsync(true);
             }
             ev->Record.AddChannels(channel.ChannelId);
         }