cleanup followers KIKIMR-15244

ref:1ceb7e9a7afb417943fa6ea2a506acf4033fd98a

3 files changed, 26 insertions, 14 deletions

diff --git a/ydb/core/mind/hive/leader_tablet_info.cpp b/ydb/core/mind/hive/leader_tablet_info.cpp
index 87205b6cfed..6345caa4db3 100644
--- a/ydb/core/mind/hive/leader_tablet_info.cpp
+++ b/ydb/core/mind/hive/leader_tablet_info.cpp
@@ -140,6 +140,16 @@ TFollowerGroup& TLeaderTabletInfo::AddFollowerGroup(TFollowerGroupId followerGro
     return followerGroup;
 }
 
+ui32 TLeaderTabletInfo::GetActualFollowerCount(TFollowerGroupId followerGroupId) const {
+    ui32 count = 0;
+    for (const auto& follower : Followers) {
+        if (follower.FollowerGroup.Id == followerGroupId) {
+            ++count;
+        }
+    }
+    return count;
+}
+
 TActorId TLeaderTabletInfo::SetLockedToActor(const TActorId& actor, const TDuration& timeout) {
     TActorId previousOwner = LockedToActor;
     if (LockedToActor != actor) {
diff --git a/ydb/core/mind/hive/leader_tablet_info.h b/ydb/core/mind/hive/leader_tablet_info.h
index 7ae56f6c00e..fd7057339d0 100644
--- a/ydb/core/mind/hive/leader_tablet_info.h
+++ b/ydb/core/mind/hive/leader_tablet_info.h
@@ -247,17 +247,11 @@ public:
 
     template <template <typename, typename...> class Cont, typename Type, typename... Types>
     static decltype(Type::Id) GenerateId(const Cont<Type, Types...>& items) {
-        decltype(Type::Id) id = 1;
-        bool retry;
-        do {
-            retry = false;
-            for (const auto& item : items) {
-                if (item.Id == id) {
-                    ++id;
-                    retry = true;
-                }
-            }
-        } while (retry);
+        decltype(Type::Id) id = 0;
+        for (const auto& item : items) {
+            id = std::max<decltype(Type::Id)>(id, item.Id);
+        }
+        ++id;
         return id;
     }
 
@@ -268,6 +262,7 @@ public:
     TFollowerTabletInfo& AddFollower(TFollowerGroup& followerGroup, TFollowerId followerId = 0);
     TFollowerGroupId GenerateFollowerGroupId() const;
     TFollowerGroup& AddFollowerGroup(TFollowerGroupId followerGroupId = 0);
+    ui32 GetActualFollowerCount(TFollowerGroupId followerGroupId) const;
 
     TFollowerGroup& GetFollowerGroup(TFollowerGroupId followerGroupId) {
         auto it = std::find(FollowerGroups.begin(), FollowerGroups.end(), followerGroupId);
diff --git a/ydb/core/mind/hive/tx__create_tablet.cpp b/ydb/core/mind/hive/tx__create_tablet.cpp
index 3bccb638882..8e92d92e53a 100644
--- a/ydb/core/mind/hive/tx__create_tablet.cpp
+++ b/ydb/core/mind/hive/tx__create_tablet.cpp
@@ -274,7 +274,7 @@ public:
                     auto itFollowerGroup = tablet->FollowerGroups.begin();
                     for (const auto& srcFollowerGroup : FollowerGroups) {
                         TFollowerGroup& followerGroup = itFollowerGroup != tablet->FollowerGroups.end() ? *itFollowerGroup : tablet->AddFollowerGroup();
-                        ui32 oldFollowerCount = followerGroup.GetComputedFollowerCount(Self->GetDataCenters());
+                        ui32 oldFollowerCount = tablet->GetActualFollowerCount(followerGroup.Id);
                         followerGroup = srcFollowerGroup;
 
                         TVector<ui32> allowedDataCenters;
@@ -302,10 +302,17 @@ public:
                         }
 
                         for (ui32 i = followerGroup.GetComputedFollowerCount(Self->GetDataCenters()); i < oldFollowerCount; ++i) {
-                            TFollowerTabletInfo& follower = tablet->Followers.back();
+                            auto itFollower = tablet->Followers.rbegin();
+                            while (itFollower != tablet->Followers.rend() && itFollower->FollowerGroup.Id != followerGroup.Id) {
+                                ++itFollower;
+                            }
+                            if (itFollower == tablet->Followers.rend()) {
+                                break;
+                            }
+                            TFollowerTabletInfo& follower = *itFollower;
                             db.Table<Schema::TabletFollowerTablet>().Key(TabletId, follower.Id).Delete();
                             follower.InitiateStop(SideEffects);
-                            tablet->Followers.pop_back();
+                            tablet->Followers.erase(std::prev(itFollower.base()));
                         }
                         ++itFollowerGroup;
                     }