Add disk time consumption metrics to dsproxy node, fix -11 crash in hive tests, KIKIMR-17759

Fix -11 crash code

Add estimatedDiskTimeConsumption metrics to dsproxy on node, KIKIMR-17759
Add estimatedDiskTimeConsumption to dsproxy on node

13 files changed, 140 insertions, 50 deletions

diff --git a/ydb/core/blobstorage/backpressure/queue.cpp b/ydb/core/blobstorage/backpressure/queue.cpp
index f16a73bcfc..0977eed6bf 100644
--- a/ydb/core/blobstorage/backpressure/queue.cpp
+++ b/ydb/core/blobstorage/backpressure/queue.cpp
@@ -11,7 +11,7 @@ TBlobStorageQueue::TBlobStorageQueue(const TIntrusivePtr<::NMonitoring::TDynamic
     , NextMsgId(0)
     , CurrentSequenceId(1)
     , LogPrefix(logPrefix)
-    , CostModel(2000, 100000000, 50000000, 540000, 540000, 500000, gType) // default cost model
+    , CostModel(std::make_shared<const TCostModel>(2000, 100000000, 50000000, 540000, 540000, 500000, gType)) // default cost model
     , BSProxyCtx(bspctx)
     , ClientId(clientId)
     , BytesWaiting(0)
@@ -52,8 +52,8 @@ TBlobStorageQueue::~TBlobStorageQueue() {
 void TBlobStorageQueue::UpdateCostModel(TInstant now, const NKikimrBlobStorage::TVDiskCostSettings& settings,
         const TBlobStorageGroupType& type) {
     TCostModel newCostModel(settings, type);
-    if (newCostModel != CostModel) {
-        CostModel = std::move(newCostModel);
+    if (newCostModel != *CostModel) {
+        CostModel = std::make_shared<const TCostModel>(std::move(newCostModel));
         InvalidateCosts();
     }
     CostSettingsUpdate = now + TDuration::Minutes(1);
@@ -78,8 +78,8 @@ bool TBlobStorageQueue::SetMaxWindowSize(ui64 maxWindowSize) {
     }
 }
 
-ui32 TBlobStorageQueue::GetMinREALHugeBlobInBytes() const {
-    return CostModel.MinREALHugeBlobInBytes;
+std::shared_ptr<const TCostModel> TBlobStorageQueue::GetCostModel() const {
+    return CostModel;
 }
 
 void TBlobStorageQueue::SetItemQueue(TItem& item, EItemQueue newQueue) {
@@ -141,7 +141,7 @@ void TBlobStorageQueue::SendToVDisk(const TActorContext& ctx, const TActorId& re
 
         // update item's cost if it is dirty
         if (item.DirtyCost) {
-            item.Cost = CostModel.CalculateCost(item.CostEssence);
+            item.Cost = CostModel->CalculateCost(item.CostEssence);
             item.DirtyCost = false;
         }
 
diff --git a/ydb/core/blobstorage/backpressure/queue.h b/ydb/core/blobstorage/backpressure/queue.h
index c5d8387e2c..f6667aef89 100644
--- a/ydb/core/blobstorage/backpressure/queue.h
+++ b/ydb/core/blobstorage/backpressure/queue.h
@@ -116,7 +116,7 @@ class TBlobStorageQueue {
 
     TString& LogPrefix;
 
-    TCostModel CostModel;
+    std::shared_ptr<const TCostModel> CostModel;
     TInstant CostSettingsUpdate;
 
     TBSProxyContextPtr BSProxyCtx;
@@ -184,7 +184,7 @@ public:
             const TBlobStorageGroupType& type);
     void InvalidateCosts();
     bool SetMaxWindowSize(ui64 maxWindowSize);
-    ui32 GetMinREALHugeBlobInBytes() const;
+    std::shared_ptr<const TCostModel> GetCostModel() const;
 
     void SetItemQueue(TItem& item, EItemQueue newQueue);
 
diff --git a/ydb/core/blobstorage/backpressure/queue_backpressure_client.cpp b/ydb/core/blobstorage/backpressure/queue_backpressure_client.cpp
index 9f4aa973f6..0fcaab8426 100644
--- a/ydb/core/blobstorage/backpressure/queue_backpressure_client.cpp
+++ b/ydb/core/blobstorage/backpressure/queue_backpressure_client.cpp
@@ -456,7 +456,7 @@ private:
             case EState::READY:
                 QLOG_NOTICE_S("BSQ96", "connection lost status# " << NKikimrProto::EReplyStatus_Name(status)
                     << " errorReason# " << errorReason << " timeout# " << timeout);
-                ctx.Send(BlobStorageProxy, new TEvProxyQueueState(VDiskId, QueueId, false, false, 0));
+                ctx.Send(BlobStorageProxy, new TEvProxyQueueState(VDiskId, QueueId, false, false, nullptr));
                 Queue.DrainQueue(status, TStringBuilder() << "BS_QUEUE: " << errorReason, ctx);
                 DrainStatus(status, ctx);
                 DrainAssimilate(status, errorReason, ctx);
@@ -563,7 +563,7 @@ private:
                 Queue.UpdateCostModel(ctx.Now(), record.GetCostSettings(), GType);
             }
             ctx.Send(BlobStorageProxy, new TEvProxyQueueState(VDiskId, QueueId, true, ExtraBlockChecksSupport,
-                Queue.GetMinREALHugeBlobInBytes()));
+                Queue.GetCostModel()));
             Queue.OnConnect();
             State = EState::READY;
         } else {
@@ -799,7 +799,7 @@ private:
             << " VDiskId# " << VDiskId
             << " IsConnected# " << isConnected);
         ctx.Send(ev->Sender, new TEvProxyQueueState(VDiskId, QueueId, isConnected, isConnected && ExtraBlockChecksSupport,
-            Queue.GetMinREALHugeBlobInBytes()));
+            Queue.GetCostModel()));
     }
 
 #define QueueRequestHFunc(TEvType) \
diff --git a/ydb/core/blobstorage/backpressure/queue_backpressure_client.h b/ydb/core/blobstorage/backpressure/queue_backpressure_client.h
index 971b8e00fa..0b80053d61 100644
--- a/ydb/core/blobstorage/backpressure/queue_backpressure_client.h
+++ b/ydb/core/blobstorage/backpressure/queue_backpressure_client.h
@@ -17,15 +17,15 @@ namespace NKikimr {
         NKikimrBlobStorage::EVDiskQueueId QueueId;
         bool IsConnected;
         bool ExtraBlockChecksSupport;
-        ui32 MinREALHugeBlobInBytes;
+        std::shared_ptr<const TCostModel> CostModel;
 
         TEvProxyQueueState(const TVDiskID &vDiskId, NKikimrBlobStorage::EVDiskQueueId queueId, bool isConnected,
-                bool extraBlockChecksSupport, ui32 minREALHugeBlobInBytes)
+                bool extraBlockChecksSupport, std::shared_ptr<const TCostModel> costModel)
             : VDiskId(vDiskId)
             , QueueId(queueId)
             , IsConnected(isConnected)
             , ExtraBlockChecksSupport(extraBlockChecksSupport)
-            , MinREALHugeBlobInBytes(minREALHugeBlobInBytes)
+            , CostModel(std::move(costModel))
         {}
 
         TString ToString() const {
@@ -34,7 +34,9 @@ namespace NKikimr {
             str << " QueueId# " << static_cast<ui32>(QueueId);
             str << " IsConnected# " << (IsConnected ? "true" : "false");
             str << " ExtraBlockChecksSupport# " << (ExtraBlockChecksSupport ? "true" : "false");
-            str << " MinREALHugeBlobInBytes# " << MinREALHugeBlobInBytes;
+            if (CostModel) {
+                str << " CostModel# " << CostModel->ToString();
+            }
             str << "}";
             return str.Str();
         }
diff --git a/ydb/core/blobstorage/dsproxy/dsproxy.h b/ydb/core/blobstorage/dsproxy/dsproxy.h
index ce7f1a2478..2a1f64a24c 100644
--- a/ydb/core/blobstorage/dsproxy/dsproxy.h
+++ b/ydb/core/blobstorage/dsproxy/dsproxy.h
@@ -178,6 +178,7 @@ public:
         , LogCtx(logComponent, logAccEnabled)
         , Span(TWilson::BlobStorage, std::move(traceId), std::move(name))
         , RestartCounter(restartCounter)
+        , CostModel(GroupQueues->CostModel)
         , Source(source)
         , Cookie(cookie)
         , LatencyQueueKind(latencyQueueKind)
@@ -189,6 +190,8 @@ public:
         Span
             .Attribute("GroupId", Info->GroupID)
             .Attribute("RestartCounter", RestartCounter);
+
+        Y_VERIFY(CostModel);
     }
 
     void Registered(TActorSystem *as, const TActorId& parentId) override {
@@ -366,7 +369,14 @@ public:
     void SendToQueue(std::unique_ptr<T> event, ui64 cookie, bool timeStatsEnabled = false) {
         if constexpr (!std::is_same_v<T, TEvBlobStorage::TEvVStatus> && !std::is_same_v<T, TEvBlobStorage::TEvVAssimilate>) {
             event->MessageRelevanceTracker = MessageRelevanceTracker;
+            if constexpr (std::is_same_v<T, TEvBlobStorage::TEvVMultiPut>) {
+                bool internalQueue;
+                SentSubrequestCost += CostModel->GetCost(*event, &internalQueue);
+            } else {
+                SentSubrequestCost += CostModel->GetCost(*event);
+            }
         }
+
         const TActorId queueId = GroupQueues->Send(*this, Info->GetTopology(), std::move(event), cookie, Span.GetTraceId(),
             timeStatsEnabled);
         ++RequestsInFlight;
@@ -499,6 +509,7 @@ public:
         if (RequestHandleClass && PoolCounters) {
             PoolCounters->GetItem(*RequestHandleClass, RequestBytes).Register(
                 RequestBytes, GeneratedSubrequests, GeneratedSubrequestBytes, Timer.Passed());
+            *PoolCounters->DSProxyDiskCostCounter += SentSubrequestCost;
         }
 
         if (timeStats) {
@@ -570,8 +581,10 @@ protected:
     ui32 RequestBytes = 0;
     ui32 GeneratedSubrequests = 0;
     ui32 GeneratedSubrequestBytes = 0;
+    ui64 SentSubrequestCost = 0;
     bool Dead = false;
     const ui32 RestartCounter = 0;
+    std::shared_ptr<const TCostModel> CostModel;
 
 private:
     const TActorId Source;
diff --git a/ydb/core/blobstorage/dsproxy/dsproxy_monactor.cpp b/ydb/core/blobstorage/dsproxy/dsproxy_monactor.cpp
index 453b31506e..09da2018d5 100644
--- a/ydb/core/blobstorage/dsproxy/dsproxy_monactor.cpp
+++ b/ydb/core/blobstorage/dsproxy/dsproxy_monactor.cpp
@@ -87,8 +87,13 @@ public:
                             str << "GroupID: " << Info->GroupID << "<br/>" << "Generation: " << Info->GroupGeneration;
                         }
                         DIV() {
-                            str << "MinREALHugeBlobInBytes: ";
-                            str << GroupQueues->MinREALHugeBlobInBytes;
+                            str << "CostModel: ";
+                            auto costModel = GroupQueues->CostModel; // acquire owning pointer
+                            if (costModel) {
+                                str << costModel->ToString();
+                            } else {
+                                str << "None";
+                            }
                         }
                         DIV() TABLE_CLASS("table table-bordered table-condensed") TABLEBODY() {
                             ui32 maxFailDomain = 0;
diff --git a/ydb/core/blobstorage/dsproxy/dsproxy_state.cpp b/ydb/core/blobstorage/dsproxy/dsproxy_state.cpp
index 0092b7d436..c74b0c09ef 100644
--- a/ydb/core/blobstorage/dsproxy/dsproxy_state.cpp
+++ b/ydb/core/blobstorage/dsproxy/dsproxy_state.cpp
@@ -206,7 +206,7 @@ namespace NKikimr {
         auto *msg = ev->Get();
         Y_VERIFY(Topology);
         Sessions->QueueConnectUpdate(Topology->GetOrderNumber(msg->VDiskId), msg->QueueId, msg->IsConnected,
-            msg->ExtraBlockChecksSupport, msg->MinREALHugeBlobInBytes, *Topology);
+            msg->ExtraBlockChecksSupport, msg->CostModel, *Topology);
         MinREALHugeBlobInBytes = Sessions->GetMinREALHugeBlobInBytes();
         if (msg->IsConnected && (CurrentStateFunc() == &TThis::StateEstablishingSessions ||
                 CurrentStateFunc() == &TThis::StateEstablishingSessionsTimeout)) {
diff --git a/ydb/core/blobstorage/dsproxy/group_sessions.cpp b/ydb/core/blobstorage/dsproxy/group_sessions.cpp
index 0ffe410e66..b56ae76421 100644
--- a/ydb/core/blobstorage/dsproxy/group_sessions.cpp
+++ b/ydb/core/blobstorage/dsproxy/group_sessions.cpp
@@ -116,49 +116,80 @@ bool TGroupSessions::GoodToGo(const TBlobStorageGroupInfo::TTopology& topology,
 }
 
 void TGroupSessions::QueueConnectUpdate(ui32 orderNumber, NKikimrBlobStorage::EVDiskQueueId queueId, bool connected,
-        bool extraGroupChecksSupport, ui32 minREALHugeBlobInBytes, const TBlobStorageGroupInfo::TTopology& topology) {
+        bool extraGroupChecksSupport, std::shared_ptr<const TCostModel> costModel, const TBlobStorageGroupInfo::TTopology& topology) {
     const auto v = topology.GetVDiskId(orderNumber);
     const ui32 fdom = topology.GetFailDomainOrderNumber(v);
     auto& f = GroupQueues->FailDomains[fdom];
     auto& vdisk = f.VDisks[v.VDisk];
     auto& q = vdisk.Queues.GetQueue(queueId);
 
+    bool updated = false;
+
     if (connected) {
         ConnectedQueuesMask[orderNumber] |= 1 << queueId;
         q.ExtraBlockChecksSupport = extraGroupChecksSupport;
-        q.MinREALHugeBlobInBytes = minREALHugeBlobInBytes;
+        Y_VERIFY(costModel);
+        if (!q.CostModel || *q.CostModel != *costModel) {
+            updated = true;
+            q.CostModel = costModel;
+        }
     } else {
         ConnectedQueuesMask[orderNumber] &= ~(1 << queueId);
         q.ExtraBlockChecksSupport.reset();
-        q.MinREALHugeBlobInBytes = 0;
+        if (q.CostModel) {
+            updated = true;
+            q.CostModel = nullptr;
+        }
     }
     q.IsConnected = connected;
 
-    auto update = [](auto& current, const auto& next) {
-        if (next.MinREALHugeBlobInBytes && (!current.MinREALHugeBlobInBytes || next.MinREALHugeBlobInBytes < current.MinREALHugeBlobInBytes)) {
-            current.MinREALHugeBlobInBytes = next.MinREALHugeBlobInBytes;
+    if (updated) {
+        auto iterate = [](auto& currentCostModel, const auto& next) {
+            if (next.CostModel) {
+                if (!currentCostModel) {
+                    currentCostModel.emplace(*next.CostModel);
+                } else {
+                    currentCostModel->PessimisticComposition(*next.CostModel);
+                }
+            }
+        };
+
+        auto update = [](std::shared_ptr<const TCostModel>& current, const std::optional<TCostModel>& recalculated) {
+            if (!recalculated) {
+                current.reset();
+            } else {
+                if (!current || *current != *recalculated) {
+                    current = std::make_shared<const TCostModel>(*recalculated);
+                }
+            }
+        };
+
+        // recalculate CostModel for the whole VDisk
+        std::optional<TCostModel> pessimistic;
+        vdisk.CostModel.reset();
+        vdisk.Queues.ForEachQueue([&](auto& q) { iterate(pessimistic, q); });
+        update(vdisk.CostModel, pessimistic);
+
+        // do the same for the fail domain
+        f.CostModel.reset();
+        pessimistic.reset();
+        for (const auto& vdisk : f.VDisks) {
+            iterate(pessimistic, vdisk);
         }
-    };
+        update(f.CostModel, pessimistic);
 
-    // recalculate MinREALHugeBlobInBytes for the whole VDisk
-    vdisk.MinREALHugeBlobInBytes = 0;
-    vdisk.Queues.ForEachQueue([&](auto& q) { update(vdisk, q); });
-
-    // do the same for the fail domain
-    f.MinREALHugeBlobInBytes = 0;
-    for (const auto& vdisk : f.VDisks) {
-        update(f, vdisk);
-    }
-
-    // and for the whole group
-    GroupQueues->MinREALHugeBlobInBytes = 0;
-    for (const auto& fdom : GroupQueues->FailDomains) {
-        update(*GroupQueues, fdom);
+        // and for the whole group
+        GroupQueues->CostModel.reset();
+        pessimistic.reset();
+        for (const auto& fdom : GroupQueues->FailDomains) {
+            iterate(pessimistic, fdom);
+        }
+        update(GroupQueues->CostModel, pessimistic);
     }
 }
 
 ui32 TGroupSessions::GetMinREALHugeBlobInBytes() const {
-    return GroupQueues->MinREALHugeBlobInBytes;
+    return GroupQueues->CostModel ? GroupQueues->CostModel->MinREALHugeBlobInBytes : 0;
 }
 
 ui32 TGroupSessions::GetNumUnconnectedDisks() {
diff --git a/ydb/core/blobstorage/dsproxy/group_sessions.h b/ydb/core/blobstorage/dsproxy/group_sessions.h
index 714159f90c..c8ce50fca8 100644
--- a/ydb/core/blobstorage/dsproxy/group_sessions.h
+++ b/ydb/core/blobstorage/dsproxy/group_sessions.h
@@ -22,7 +22,7 @@ namespace NKikimr {
                     TActorId ActorId;
                     TIntrusivePtr<NBackpressure::TFlowRecord> FlowRecord;
                     std::optional<bool> ExtraBlockChecksSupport;
-                    ui32 MinREALHugeBlobInBytes = 0;
+                    std::shared_ptr<const TCostModel> CostModel = nullptr;
                     volatile bool IsConnected = false;
                 };
                 TQueue PutTabletLog;
@@ -133,7 +133,7 @@ namespace NKikimr {
             };
 
             TQueues Queues;
-            ui32 MinREALHugeBlobInBytes = 0;
+            std::shared_ptr<const TCostModel> CostModel;
 
             TString ToString() const {
                 return TStringBuilder() << "{Queues# " << Queues.ToString() << "}";
@@ -142,7 +142,7 @@ namespace NKikimr {
 
         struct TFailDomain {
             TStackVec<TVDisk, TypicalDisksInFailDomain> VDisks;
-            ui32 MinREALHugeBlobInBytes = 0;
+            std::shared_ptr<const TCostModel> CostModel;
 
             // Ill-formed because TVDisk is not assignable.
             TFailDomain(const TFailDomain& other) = default;
@@ -162,7 +162,7 @@ namespace NKikimr {
 
         TStackVec<TFailDomain, TypicalFailDomainsInGroup> FailDomains;
         TStackVec<TVDisk*, TypicalDisksInGroup> DisksByOrderNumber;
-        ui32 MinREALHugeBlobInBytes = 0;
+        std::shared_ptr<const TCostModel> CostModel;
 
         TGroupQueues(const TBlobStorageGroupInfo::TTopology& topology)
             : FailDomains(topology.GetTotalFailDomainsNum())
@@ -246,7 +246,7 @@ namespace NKikimr {
         void Poison();
         bool GoodToGo(const TBlobStorageGroupInfo::TTopology& topology, bool waitForAllVDisks);
         void QueueConnectUpdate(ui32 orderNumber, NKikimrBlobStorage::EVDiskQueueId queueId, bool connected,
-            bool extraBlockChecksSupport, ui32 minREALHugeBlobInBytes, const TBlobStorageGroupInfo::TTopology& topology);
+            bool extraBlockChecksSupport, std::shared_ptr<const TCostModel> costModel, const TBlobStorageGroupInfo::TTopology& topology);
         ui32 GetNumUnconnectedDisks();
         ui32 GetMinREALHugeBlobInBytes() const;
     };
diff --git a/ydb/core/blobstorage/storagepoolmon/storagepool_counters.h b/ydb/core/blobstorage/storagepoolmon/storagepool_counters.h
index 0eb004ec16..de923b6bb7 100644
--- a/ydb/core/blobstorage/storagepoolmon/storagepool_counters.h
+++ b/ydb/core/blobstorage/storagepoolmon/storagepool_counters.h
@@ -149,6 +149,8 @@ private:
     TRequestMonItem RequestMon[HcCount][MaxSizeClassBucketIdx + 1];
     TString StoragePoolName;
 
+    TIntrusivePtr<::NMonitoring::TDynamicCounters> PoolGroup;
+
 public:
     TRequestMonItem& GetItem(EHandleClass handleClass, ui32 requestBytes) {
         Y_VERIFY((ui32)handleClass < (ui32)HcCount);
@@ -164,12 +166,13 @@ public:
     }
 
     TStoragePoolCounters(TIntrusivePtr<::NMonitoring::TDynamicCounters> &counters, const TString &storagePoolName,
-            NPDisk::EDeviceType type) {
-        StoragePoolName = storagePoolName;
-        TIntrusivePtr<::NMonitoring::TDynamicCounters> poolGroup = counters->GetSubgroup("storagePool", storagePoolName);
+            NPDisk::EDeviceType type)
+        : StoragePoolName(storagePoolName)
+        , PoolGroup(counters->GetSubgroup("storagePool", storagePoolName))
+    {
         for (ui32 handleClass = 0; handleClass < (ui32)HcCount; ++handleClass) {
             TString handleClassName = GetHandleClassName((EHandleClass)handleClass);
-            TIntrusivePtr<::NMonitoring::TDynamicCounters> hcGroup = poolGroup->GetSubgroup("handleClass", handleClassName);
+            TIntrusivePtr<::NMonitoring::TDynamicCounters> hcGroup = PoolGroup->GetSubgroup("handleClass", handleClassName);
             if (IsReducedHandleClass((EHandleClass)handleClass)) {
                 for (ui32 sizeClassIdx = 0; sizeClassIdx <= MaxReducedSizeClassBucketIdx; ++sizeClassIdx) {
                     TString sizeClassName = ReducedSizeClassName(sizeClassIdx);
@@ -182,8 +185,17 @@ public:
                 }
             }
         }
+
+        // request cost counters
+        {
+            auto group = PoolGroup->GetSubgroup("subsystem", "cost");
+            DSProxyDiskCostCounter = group->GetCounter("DSProxyDiskCostNs", true);
+        }
     }
 
+public:
+    // request cost counters
+    ::NMonitoring::TDynamicCounters::TCounterPtr DSProxyDiskCostCounter;
 };
 
 class TDsProxyPerPoolCounters : public TThrRefBase {
diff --git a/ydb/core/blobstorage/ut_vdisk/lib/helpers.cpp b/ydb/core/blobstorage/ut_vdisk/lib/helpers.cpp
index 884673b2ed..48ea78f3bd 100644
--- a/ydb/core/blobstorage/ut_vdisk/lib/helpers.cpp
+++ b/ydb/core/blobstorage/ut_vdisk/lib/helpers.cpp
@@ -413,7 +413,7 @@ class TManyMultiPuts : public TActorBootstrapped<TManyMultiPuts> {
     void Handle(TEvProxyQueueState::TPtr& ev, const TActorContext& ctx) {
         if (ev->Get()->IsConnected && !Started) {
             // put logo blob
-            MinREALHugeBlobInBytes = ev->Get()->MinREALHugeBlobInBytes;
+            MinREALHugeBlobInBytes = ev->Get()->CostModel->MinREALHugeBlobInBytes;
             Y_VERIFY(MinREALHugeBlobInBytes);
             SendPut(ctx);
             Started = true;
diff --git a/ydb/core/blobstorage/vdisk/common/vdisk_costmodel.cpp b/ydb/core/blobstorage/vdisk/common/vdisk_costmodel.cpp
index 3acfe26ea3..4a6921a34e 100644
--- a/ydb/core/blobstorage/vdisk/common/vdisk_costmodel.cpp
+++ b/ydb/core/blobstorage/vdisk/common/vdisk_costmodel.cpp
@@ -153,4 +153,26 @@ namespace NKikimr {
         return cost;
     }
 
+    TString TCostModel::ToString() const {
+        TStringStream str;
+        str << "{SeekTimeUs# " << SeekTimeUs;
+        str << " ReadSpeedBps# " << ReadSpeedBps;
+        str << " WriteSpeedBps# " << WriteSpeedBps;
+        str << " ReadBlockSize# " << ReadBlockSize;
+        str << " WriteBlockSize# " << WriteBlockSize;
+        str << " MinREALHugeBlobInBytes# " << MinREALHugeBlobInBytes;
+        str << " GType# " << GType.ToString();
+        str << "}";
+        return str.Str();
+    }
+
+    void TCostModel::PessimisticComposition(const TCostModel& other) {
+        SeekTimeUs = std::max(SeekTimeUs, other.SeekTimeUs);
+        ReadSpeedBps = std::min(ReadSpeedBps, other.ReadSpeedBps);
+        WriteSpeedBps = std::min(WriteSpeedBps, other.WriteSpeedBps);
+        ReadBlockSize = std::min(ReadBlockSize, other.ReadBlockSize);
+        WriteBlockSize = std::min(WriteBlockSize, other.WriteBlockSize);
+        MinREALHugeBlobInBytes = std::max(MinREALHugeBlobInBytes, other.MinREALHugeBlobInBytes);
+    }
+
 } // NKikimr
diff --git a/ydb/core/blobstorage/vdisk/common/vdisk_costmodel.h b/ydb/core/blobstorage/vdisk/common/vdisk_costmodel.h
index eb16996c30..d072757471 100644
--- a/ydb/core/blobstorage/vdisk/common/vdisk_costmodel.h
+++ b/ydb/core/blobstorage/vdisk/common/vdisk_costmodel.h
@@ -216,6 +216,11 @@ namespace NKikimr {
         ui64 MovedPatchCostBySize(ui32 blobSize) const;
         ui64 ReadCostBySize(ui64 size) const;
         ui64 ReadCost(const TEvBlobStorage::TEvVGet &ev) const;
+
+    public:
+        TString ToString() const;
+        void PessimisticComposition(const TCostModel& other);
+
     };
 
 } // NKikimr