conclusions for unready storages and scanner methods (#3282)

17 files changed, 110 insertions, 131 deletions

diff --git a/ydb/core/tx/columnshard/counters/scan.h b/ydb/core/tx/columnshard/counters/scan.h
index 7103e2f115..3469dc2898 100644
--- a/ydb/core/tx/columnshard/counters/scan.h
+++ b/ydb/core/tx/columnshard/counters/scan.h
@@ -45,9 +45,11 @@ public:
         Success /* "Success" */ = 0,
         ConveyorInternalError /* "ConveyorInternalError" */,
         ExternalAbort /* "ExternalAbort" */,
-        IteratorInternalError /* "IteratorInternalError" */,
+        IteratorInternalErrorScan /* "IteratorInternalErrorScan" */,
+        IteratorInternalErrorResult /* "IteratorInternalErrorResult" */,
         Deadline /* "Deadline" */,
         UndeliveredEvent /* "UndeliveredEvent" */,
+        CannotAddInFlight /* "CannotAddInFlight" */,
 
         COUNT
     };
diff --git a/ydb/core/tx/columnshard/engines/reader/abstract/abstract.h b/ydb/core/tx/columnshard/engines/reader/abstract/abstract.h
index c19f00e400..734f18bc5b 100644
--- a/ydb/core/tx/columnshard/engines/reader/abstract/abstract.h
+++ b/ydb/core/tx/columnshard/engines/reader/abstract/abstract.h
@@ -19,11 +19,11 @@ public:
         return {};
     }
     virtual bool Finished() const = 0;
-    virtual std::optional<TPartialReadResult> GetBatch() = 0;
+    virtual TConclusion<std::optional<TPartialReadResult>> GetBatch() = 0;
     virtual void PrepareResults() {
 
     }
-    virtual bool ReadNextInterval() { return false; }
+    virtual TConclusion<bool> ReadNextInterval() { return false; }
     virtual TString DebugString(const bool verbose = false) const {
         Y_UNUSED(verbose);
         return "NO_DATA";
diff --git a/ydb/core/tx/columnshard/engines/reader/abstract/read_context.h b/ydb/core/tx/columnshard/engines/reader/abstract/read_context.h
index d88266eb81..af1b5ab5bb 100644
--- a/ydb/core/tx/columnshard/engines/reader/abstract/read_context.h
+++ b/ydb/core/tx/columnshard/engines/reader/abstract/read_context.h
@@ -108,7 +108,7 @@ protected:
     virtual void DoAbort() = 0;
     virtual bool DoIsFinished() const = 0;
     virtual std::vector<TPartialReadResult> DoExtractReadyResults(const int64_t maxRowsInBatch) = 0;
-    virtual bool DoReadNextInterval() = 0;
+    virtual TConclusion<bool> DoReadNextInterval() = 0;
 public:
     IDataReader(const std::shared_ptr<TReadContext>& context);
     virtual ~IDataReader() = default;
@@ -156,7 +156,7 @@ public:
         sb << DoDebugString(verbose);
         return sb;
     }
-    bool ReadNextInterval() {
+    [[nodiscard]] TConclusion<bool> ReadNextInterval() {
         return DoReadNextInterval();
     }
 };
diff --git a/ydb/core/tx/columnshard/engines/reader/actor/actor.cpp b/ydb/core/tx/columnshard/engines/reader/actor/actor.cpp
index a3805f3c4b..49ab834d3f 100644
--- a/ydb/core/tx/columnshard/engines/reader/actor/actor.cpp
+++ b/ydb/core/tx/columnshard/engines/reader/actor/actor.cpp
@@ -45,7 +45,7 @@ void TColumnShardScan::PassAway() {
 
 TColumnShardScan::TColumnShardScan(const TActorId& columnShardActorId, const TActorId& scanComputeActorId, const std::shared_ptr<IStoragesManager>& storagesManager, 
     const TComputeShardingPolicy& computeShardingPolicy, ui32 scanId, ui64 txId, ui32 scanGen, ui64 requestCookie, 
-    ui64 tabletId, TDuration timeout, std::vector<TReadMetadataBase::TConstPtr>&& readMetadataList,
+    ui64 tabletId, TDuration timeout, const TReadMetadataBase::TConstPtr& readMetadataRange,
     NKikimrDataEvents::EDataFormat dataFormat, const NColumnShard::TScanCounters& scanCountersPool)
     : StoragesManager(storagesManager)
     , ColumnShardActorId(columnShardActorId)
@@ -57,15 +57,14 @@ TColumnShardScan::TColumnShardScan(const TActorId& columnShardActorId, const TAc
     , RequestCookie(requestCookie)
     , DataFormat(dataFormat)
     , TabletId(tabletId)
-    , ReadMetadataRanges(std::move(readMetadataList))
-    , ReadMetadataIndex(0)
+    , ReadMetadataRange(readMetadataRange)
     , Deadline(TInstant::Now() + (timeout ? timeout + SCAN_HARD_TIMEOUT_GAP : SCAN_HARD_TIMEOUT))
     , ScanCountersPool(scanCountersPool)
     , Stats(NTracing::TTraceClient::GetLocalClient("SHARD", ::ToString(TabletId)/*, "SCAN_TXID:" + ::ToString(TxId)*/))
     , ComputeShardingPolicy(computeShardingPolicy)
 {
-    AFL_VERIFY(ReadMetadataRanges.size() == 1);
-    KeyYqlSchema = ReadMetadataRanges[ReadMetadataIndex]->GetKeyYqlSchema();
+    AFL_VERIFY(ReadMetadataRange);
+    KeyYqlSchema = ReadMetadataRange->GetKeyYqlSchema();
 }
 
 void TColumnShardScan::Bootstrap(const TActorContext& ctx) {
@@ -81,8 +80,8 @@ void TColumnShardScan::Bootstrap(const TActorContext& ctx) {
     ReadCoordinatorActorId = ctx.Register(new NBlobOperations::NRead::TReadCoordinatorActor(TabletId, SelfId()));
 
     std::shared_ptr<TReadContext> context = std::make_shared<TReadContext>(StoragesManager, ScanCountersPool,
-        ReadMetadataRanges[ReadMetadataIndex], SelfId(), ResourceSubscribeActorId, ReadCoordinatorActorId, ComputeShardingPolicy);
-    ScanIterator = ReadMetadataRanges[ReadMetadataIndex]->StartScan(context);
+        ReadMetadataRange, SelfId(), ResourceSubscribeActorId, ReadCoordinatorActorId, ComputeShardingPolicy);
+    ScanIterator = ReadMetadataRange->StartScan(context);
 
     // propagate self actor id // TODO: FlagSubscribeOnSession ?
     Send(ScanComputeActorId, new NKqp::TEvKqpCompute::TEvScanInitActor(ScanId, ctx.SelfID, ScanGen, TabletId), IEventHandle::FlagTrackDelivery);
@@ -92,12 +91,6 @@ void TColumnShardScan::Bootstrap(const TActorContext& ctx) {
     ContinueProcessing();
 }
 
-bool TColumnShardScan::ReadNextBlob() {
-    while (ScanIterator->ReadNextInterval()) {
-    }
-    return true;
-}
-
 void TColumnShardScan::HandleScan(NConveyor::TEvExecution::TEvTaskProcessedResult::TPtr& ev) {
     --InFlightReads;
     auto g = Stats->MakeGuard("task_result");
@@ -198,21 +191,24 @@ bool TColumnShardScan::ProduceResults() noexcept {
         return false;
     }
 
-    auto resultOpt = ScanIterator->GetBatch();
-    if (!resultOpt) {
-        ACFL_DEBUG("stage", "no data is ready yet")("iterator", ScanIterator->DebugString());
+    auto resultConclusion = ScanIterator->GetBatch();
+    if (resultConclusion.IsFail()) {
+        ACFL_ERROR("stage", "got error")("iterator", ScanIterator->DebugString())("message", resultConclusion.GetErrorMessage());
+        SendAbortExecution(resultConclusion.GetErrorMessage());
+
+        ScanIterator.reset();
+        Finish(NColumnShard::TScanCounters::EStatusFinish::IteratorInternalErrorResult);
         return false;
     }
-    auto& result = *resultOpt;
-    if (!result.ErrorString.empty()) {
-        ACFL_ERROR("stage", "got error")("iterator", ScanIterator->DebugString())("message", result.ErrorString);
-        SendAbortExecution(TString(result.ErrorString.data(), result.ErrorString.size()));
 
-        ScanIterator.reset();
-        Finish(NColumnShard::TScanCounters::EStatusFinish::IteratorInternalError);
+    std::optional<TPartialReadResult> resultOpt = resultConclusion.DetachResult();
+    if (!resultOpt) {
+        ACFL_DEBUG("stage", "no data is ready yet")("iterator", ScanIterator->DebugString());
         return false;
     }
 
+    auto& result = *resultOpt;
+
     if (!result.GetRecordsCount()) {
         ACFL_DEBUG("stage", "got empty batch")("iterator", ScanIterator->DebugString());
         return true;
@@ -263,14 +259,27 @@ void TColumnShardScan::ContinueProcessing() {
     while (ScanIterator && ProduceResults()) {
     }
 
-    // Switch to the next range if the current one is finished
-    if (ScanIterator && ScanIterator->Finished() && ChunksLimiter.HasMore()) {
-        NextReadMetadata();
-    }
-
     if (ScanIterator) {
-        // Make read-ahead requests for the subsequent blobs
-        ReadNextBlob();
+        // Switch to the next range if the current one is finished
+        if (ScanIterator->Finished() && ChunksLimiter.HasMore()) {
+            auto g = Stats->MakeGuard("Finish");
+            MakeResult();
+            SendResult(false, true);
+            ScanIterator.reset();
+            Finish(NColumnShard::TScanCounters::EStatusFinish::Success);
+        } else {
+            while (true) {
+                TConclusion<bool> hasMoreData = ScanIterator->ReadNextInterval();
+                if (hasMoreData.IsFail()) {
+                    ACFL_ERROR("event", "ContinueProcessing")("error", hasMoreData.GetErrorMessage());
+                    ScanIterator.reset();
+                    SendScanError("iterator_error:" + hasMoreData.GetErrorMessage());
+                    return Finish(NColumnShard::TScanCounters::EStatusFinish::IteratorInternalErrorScan);
+                } else if (!*hasMoreData) {
+                    break;
+                }
+            }
+        }
     }
     AFL_VERIFY(!ScanIterator || !ChunksLimiter.HasMore() || InFlightReads || ScanCountersPool.InWaiting())("scan_actor_id", ScanActorId)("tx_id", TxId)("scan_id", ScanId)("gen", ScanGen)("tablet", TabletId)
         ("debug", ScanIterator->DebugString());
@@ -286,21 +295,6 @@ void TColumnShardScan::MakeResult(size_t reserveRows /*= 0*/) {
     }
 }
 
-void TColumnShardScan::NextReadMetadata() {
-    auto g = Stats->MakeGuard("NextReadMetadata");
-    if (++ReadMetadataIndex == ReadMetadataRanges.size()) {
-        // Send empty batch with "finished" flag
-        MakeResult();
-        SendResult(false, true);
-        ScanIterator.reset();
-        return Finish(NColumnShard::TScanCounters::EStatusFinish::Success);
-    }
-
-    auto context = std::make_shared<TReadContext>(StoragesManager, ScanCountersPool, ReadMetadataRanges[ReadMetadataIndex], SelfId(),
-        ResourceSubscribeActorId, ReadCoordinatorActorId, ComputeShardingPolicy);
-    ScanIterator = ReadMetadataRanges[ReadMetadataIndex]->StartScan(context);
-}
-
 void TColumnShardScan::AddRow(const TConstArrayRef<TCell>& row) {
     Result->Rows.emplace_back(TOwnedCellVec::Make(row));
     ++Rows;
@@ -379,11 +373,10 @@ bool TColumnShardScan::SendResult(bool pageFault, bool lastBatch) {
     return true;
 }
 
-void TColumnShardScan::SendScanError(TString reason /*= {}*/) {
+void TColumnShardScan::SendScanError(const TString& reason) {
+    AFL_VERIFY(reason);
     TString msg = TStringBuilder() << "Scan failed at tablet " << TabletId;
-    if (!reason.empty()) {
-        msg += ", reason: " + reason;
-    }
+    msg += ", reason: " + reason;
 
     auto ev = MakeHolder<NKqp::TEvKqpCompute::TEvScanError>(ScanGen, TabletId);
     ev->Record.SetStatus(Ydb::StatusIds::GENERIC_ERROR);
@@ -393,12 +386,11 @@ void TColumnShardScan::SendScanError(TString reason /*= {}*/) {
     Send(ScanComputeActorId, ev.Release());
 }
 
-void TColumnShardScan::SendAbortExecution(TString reason /*= {}*/) {
+void TColumnShardScan::SendAbortExecution(const TString& reason) {
+    AFL_VERIFY(reason);
     auto status = NYql::NDqProto::StatusIds::PRECONDITION_FAILED;
     TString msg = TStringBuilder() << "Scan failed at tablet " << TabletId;
-    if (!reason.empty()) {
-        msg += ", reason: " + reason;
-    }
+    msg += ", reason: " + reason;
 
     Send(ScanComputeActorId, new NKqp::TEvKqp::TEvAbortExecution(status, msg));
 }
diff --git a/ydb/core/tx/columnshard/engines/reader/actor/actor.h b/ydb/core/tx/columnshard/engines/reader/actor/actor.h
index 234fb17823..1ae46d783e 100644
--- a/ydb/core/tx/columnshard/engines/reader/actor/actor.h
+++ b/ydb/core/tx/columnshard/engines/reader/actor/actor.h
@@ -33,7 +33,7 @@ public:
     TColumnShardScan(const TActorId& columnShardActorId, const TActorId& scanComputeActorId,
         const std::shared_ptr<IStoragesManager>& storagesManager, const TComputeShardingPolicy& computeShardingPolicy,
         ui32 scanId, ui64 txId, ui32 scanGen, ui64 requestCookie,
-        ui64 tabletId, TDuration timeout, std::vector<TReadMetadataBase::TConstPtr>&& readMetadataList,
+        ui64 tabletId, TDuration timeout, const TReadMetadataBase::TConstPtr& readMetadataRange,
         NKikimrDataEvents::EDataFormat dataFormat, const NColumnShard::TScanCounters& scanCountersPool);
 
     void Bootstrap(const TActorContext& ctx);
@@ -55,8 +55,6 @@ private:
         }
     }
 
-    bool ReadNextBlob();
-
     void HandleScan(NConveyor::TEvExecution::TEvTaskProcessedResult::TPtr& ev);
 
     void HandleScan(NKqp::TEvKqpCompute::TEvScanDataAck::TPtr& ev);
@@ -75,8 +73,6 @@ private:
 private:
     void MakeResult(size_t reserveRows = 0);
 
-    void NextReadMetadata();
-
     void AddRow(const TConstArrayRef<TCell>& row) override;
 
     TOwnedCellVec ConvertLastKey(const std::shared_ptr<arrow::RecordBatch>& lastReadKey);
@@ -101,9 +97,9 @@ private:
 
     bool SendResult(bool pageFault, bool lastBatch);
 
-    void SendScanError(TString reason = {});
+    void SendScanError(const TString& reason);
 
-    void SendAbortExecution(TString reason = {});
+    void SendAbortExecution(const TString& reason);
 
     void Finish(const NColumnShard::TScanCounters::EStatusFinish status);
 
@@ -123,8 +119,7 @@ private:
     const NKikimrDataEvents::EDataFormat DataFormat;
     const ui64 TabletId;
 
-    std::vector<TReadMetadataBase::TConstPtr> ReadMetadataRanges;
-    ui32 ReadMetadataIndex;
+    TReadMetadataBase::TConstPtr ReadMetadataRange;
     std::unique_ptr<TScanIteratorBase> ScanIterator;
 
     std::vector<std::pair<TString, NScheme::TTypeInfo>> KeyYqlSchema;
diff --git a/ydb/core/tx/columnshard/engines/reader/common/result.h b/ydb/core/tx/columnshard/engines/reader/common/result.h
index 8b575d8a26..cfa9ebe87e 100644
--- a/ydb/core/tx/columnshard/engines/reader/common/result.h
+++ b/ydb/core/tx/columnshard/engines/reader/common/result.h
@@ -54,8 +54,6 @@ public:
         return LastReadKey;
     }
 
-    std::string ErrorString;
-
     explicit TPartialReadResult(
         const std::vector<std::shared_ptr<NResourceBroker::NSubscribe::TResourcesGuard>>& resourcesGuards,
         const NArrow::TShardedRecordBatch& batch, std::shared_ptr<arrow::RecordBatch> lastKey)
diff --git a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/iterator.cpp b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/iterator.cpp
index e8b33132b0..c8de567ad8 100644
--- a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/iterator.cpp
+++ b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/iterator.cpp
@@ -15,7 +15,7 @@ TColumnShardScanIterator::TColumnShardScanIterator(const std::shared_ptr<TReadCo
     }
 }
 
-std::optional<TPartialReadResult> TColumnShardScanIterator::GetBatch() {
+TConclusion<std::optional<TPartialReadResult>> TColumnShardScanIterator::GetBatch() {
     FillReadyResults();
     return ReadyResults.pop_front();
 }
@@ -24,7 +24,7 @@ void TColumnShardScanIterator::PrepareResults() {
     FillReadyResults();
 }
 
-bool TColumnShardScanIterator::ReadNextInterval() {
+TConclusion<bool> TColumnShardScanIterator::ReadNextInterval() {
     return IndexedData->ReadNextInterval();
 }
 
diff --git a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/iterator.h b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/iterator.h
index beba3b2733..61c3c97007 100644
--- a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/iterator.h
+++ b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/iterator.h
@@ -83,10 +83,10 @@ public:
         return IndexedData->IsFinished() && ReadyResults.empty();
     }
 
-    std::optional<TPartialReadResult> GetBatch() override;
+    TConclusion<std::optional<TPartialReadResult>> GetBatch() override;
     virtual void PrepareResults() override;
 
-    virtual bool ReadNextInterval() override;
+    virtual TConclusion<bool> ReadNextInterval() override;
 
 private:
     void FillReadyResults();
diff --git a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/plain_read_data.cpp b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/plain_read_data.cpp
index 1f362c00cc..875acea032 100644
--- a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/plain_read_data.cpp
+++ b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/plain_read_data.cpp
@@ -69,7 +69,7 @@ std::vector<TPartialReadResult> TPlainReadData::DoExtractReadyResults(const int6
     return result;
 }
 
-bool TPlainReadData::DoReadNextInterval() {
+TConclusion<bool> TPlainReadData::DoReadNextInterval() {
     return Scanner->BuildNextInterval();
 }
 
diff --git a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/plain_read_data.h b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/plain_read_data.h
index 07946d5195..0df41d3a9a 100644
--- a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/plain_read_data.h
+++ b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/plain_read_data.h
@@ -28,7 +28,7 @@ protected:
     }
 
     virtual std::vector<TPartialReadResult> DoExtractReadyResults(const int64_t maxRowsInBatch) override;
-    virtual bool DoReadNextInterval() override;
+    virtual TConclusion<bool> DoReadNextInterval() override;
 
     virtual void DoAbort() override {
         AbortedFlag = true;
diff --git a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/scanner.cpp b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/scanner.cpp
index 11f284f14f..51de7b6d84 100644
--- a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/scanner.cpp
+++ b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/scanner.cpp
@@ -76,7 +76,7 @@ TScanHead::TScanHead(std::deque<std::shared_ptr<IDataSource>>&& sources, const s
     }
 }
 
-bool TScanHead::BuildNextInterval() {
+TConclusion<bool> TScanHead::BuildNextInterval() {
     while (BorderPoints.size() && (FetchingIntervals.size() < InFlightLimit || BorderPoints.begin()->second.GetStartSources().empty())) {
         auto firstBorderPointInfo = std::move(BorderPoints.begin()->second);
         bool includeStart = firstBorderPointInfo.GetStartSources().size();
diff --git a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/scanner.h b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/scanner.h
index a2ca7f3861..5465ec0330 100644
--- a/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/scanner.h
+++ b/ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/scanner.h
@@ -69,7 +69,7 @@ public:
 
     TScanHead(std::deque<std::shared_ptr<IDataSource>>&& sources, const std::shared_ptr<TSpecialReadContext>& context);
 
-    bool BuildNextInterval();
+    [[nodiscard]] TConclusion<bool> BuildNextInterval();
 
 };
 
diff --git a/ydb/core/tx/columnshard/engines/reader/sys_view/abstract/abstract.h b/ydb/core/tx/columnshard/engines/reader/sys_view/abstract/abstract.h
index 63fcd76852..37a9855703 100644
--- a/ydb/core/tx/columnshard/engines/reader/sys_view/abstract/abstract.h
+++ b/ydb/core/tx/columnshard/engines/reader/sys_view/abstract/abstract.h
@@ -89,7 +89,7 @@ protected:
 
     std::deque<std::shared_ptr<TPortionInfo>> IndexPortions;
 
-    virtual std::optional<TPartialReadResult> GetBatch() override {
+    virtual TConclusion<std::optional<TPartialReadResult>> GetBatch() override {
         // Take next raw batch
         auto batch = FillStatsBatch();
 
@@ -99,13 +99,13 @@ protected:
 
         ApplyRangePredicates(batch);
         if (!batch->num_rows()) {
-            return {};
+            return std::nullopt;
         }
         // Leave only requested columns
         auto resultBatch = NArrow::ExtractColumns(batch, ResultSchema);
         NArrow::TStatusValidator::Validate(ReadMetadata->GetProgram().ApplyProgram(resultBatch));
         if (!resultBatch->num_rows()) {
-            return {};
+            return std::nullopt;
         }
         TPartialReadResult out(resultBatch, lastKey);
 
diff --git a/ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.cpp b/ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.cpp
index 988a2b60a6..c7a3ff6b23 100644
--- a/ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.cpp
+++ b/ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.cpp
@@ -150,20 +150,18 @@ bool TTxScan::Execute(TTransactionContext& /*txc*/, const TActorContext& /*ctx*/
     if (!record.RangesSize()) {
         auto range = scannerConstructor->BuildReadMetadata(Self, read);
         if (range) {
-            ReadMetadataRanges = {range.DetachResult()};
+            ReadMetadataRange = range.DetachResult();
         } else {
             ErrorDescription = range.GetErrorMessage();
         }
         return true;
     }
 
-    ReadMetadataRanges.reserve(1);
-
     auto ydbKey = scannerConstructor->GetPrimaryKeyScheme(Self);
     auto* indexInfo = (vIndex && isIndex) ? &vIndex->GetSchema(snapshot)->GetIndexInfo() : nullptr;
     for (auto& range : record.GetRanges()) {
         if (!FillPredicatesFromRange(read, range, ydbKey, Self->TabletID(), indexInfo, ErrorDescription)) {
-            ReadMetadataRanges.clear();
+            ReadMetadataRange = nullptr;
             return true;
         }
     }
@@ -171,13 +169,12 @@ bool TTxScan::Execute(TTransactionContext& /*txc*/, const TActorContext& /*ctx*/
         auto newRange = scannerConstructor->BuildReadMetadata(Self, read);
         if (!newRange) {
             ErrorDescription = newRange.GetErrorMessage();
-            ReadMetadataRanges.clear();
+            ReadMetadataRange = nullptr;
             return true;
         }
-        ReadMetadataRanges.emplace_back(newRange.DetachResult());
+        ReadMetadataRange = newRange.DetachResult();
     }
-    Y_ABORT_UNLESS(ReadMetadataRanges.size() == 1);
-
+    AFL_VERIFY(ReadMetadataRange);
     return true;
 }
 
@@ -198,6 +195,7 @@ struct TContainerPrinter {
 };
 
 void TTxScan::Complete(const TActorContext& ctx) {
+
     auto& request = Ev->Get()->Record;
     auto scanComputeActor = Ev->Sender;
     const auto& snapshot = request.GetSnapshot();
@@ -210,38 +208,43 @@ void TTxScan::Complete(const TActorContext& ctx) {
     if (scanGen > 1) {
         Self->IncCounter(NColumnShard::COUNTER_SCAN_RESTARTED);
     }
+    const NActors::TLogContextGuard gLogging = NActors::TLogContextBuilder::Build()
+        ("tx_id", txId)("scan_id", scanId)("gen", scanGen)("table", table)("snapshot", snapshot)("tablet", Self->TabletID())("timeout", timeout);
 
-    TStringStream detailedInfo;
-    if (IS_LOG_PRIORITY_ENABLED(NActors::NLog::PRI_TRACE, NKikimrServices::TX_COLUMNSHARD)) {
-        detailedInfo << " read metadata: (" << TContainerPrinter(ReadMetadataRanges) << ")" << " req: " << request;
-    }
-    if (ReadMetadataRanges.empty()) {
-        LOG_S_DEBUG("TTxScan failed "
-            << " txId: " << txId
-            << " scanId: " << scanId
-            << " gen: " << scanGen
-            << " table: " << table
-            << " snapshot: " << snapshot
-            << " timeout: " << timeout
-            << detailedInfo.Str()
-            << " at tablet " << Self->TabletID());
+    if (!ReadMetadataRange) {
+        AFL_WARN(NKikimrServices::TX_COLUMNSHARD_SCAN)("event", "TTxScan failed")("reason", "no metadata");
 
         auto ev = MakeHolder<NKqp::TEvKqpCompute::TEvScanError>(scanGen, Self->TabletID());
-
         ev->Record.SetStatus(Ydb::StatusIds::BAD_REQUEST);
         auto issue = NYql::YqlIssue({}, NYql::TIssuesIds::KIKIMR_BAD_REQUEST, TStringBuilder()
-            << "Table " << table << " (shard " << Self->TabletID() << ") scan failed, reason: " << ErrorDescription ? ErrorDescription : "unknown error");
+            << "Table " << table << " (shard " << Self->TabletID() << ") scan failed, reason: " << ErrorDescription ? ErrorDescription : "no metadata ranges");
         NYql::IssueToMessage(issue, ev->Record.MutableIssues()->Add());
 
         ctx.Send(scanComputeActor, ev.Release());
         return;
     }
+    TStringBuilder detailedInfo;
+    if (IS_LOG_PRIORITY_ENABLED(NActors::NLog::PRI_TRACE, NKikimrServices::TX_COLUMNSHARD)) {
+        detailedInfo << " read metadata: (" << *ReadMetadataRange << ")" << " req: " << request;
+    }
 
     const TVersionedIndex* index = nullptr;
     if (Self->HasIndex()) {
         index = &Self->GetIndexAs<TColumnEngineForLogs>().GetVersionedIndex();
     }
-    ui64 requestCookie = Self->InFlightReadsTracker.AddInFlightRequest(ReadMetadataRanges, index);
+    const TConclusion<ui64> requestCookie = Self->InFlightReadsTracker.AddInFlightRequest(ReadMetadataRange, index);
+    if (!requestCookie) {
+        AFL_ERROR(NKikimrServices::TX_COLUMNSHARD_SCAN)("event", "TTxScan failed")("reason", requestCookie.GetErrorMessage())("trace_details", detailedInfo);
+        auto ev = MakeHolder<NKqp::TEvKqpCompute::TEvScanError>(scanGen, Self->TabletID());
+
+        ev->Record.SetStatus(Ydb::StatusIds::INTERNAL_ERROR);
+        auto issue = NYql::YqlIssue({}, NYql::TIssuesIds::KIKIMR_TEMPORARILY_UNAVAILABLE, TStringBuilder()
+            << "Table " << table << " (shard " << Self->TabletID() << ") scan failed, reason: " << requestCookie.GetErrorMessage());
+        NYql::IssueToMessage(issue, ev->Record.MutableIssues()->Add());
+        Self->ScanCounters.OnScanDuration(NColumnShard::TScanCounters::EStatusFinish::CannotAddInFlight, TDuration::Zero());
+        ctx.Send(scanComputeActor, ev.Release());
+        return;
+    }
     auto statsDelta = Self->InFlightReadsTracker.GetSelectStatsDelta();
 
     Self->IncCounter(NColumnShard::COUNTER_READ_INDEX_PORTIONS, statsDelta.Portions);
@@ -253,17 +256,9 @@ void TTxScan::Complete(const TActorContext& ctx) {
     AFL_VERIFY(shardingPolicy.DeserializeFromProto(request.GetComputeShardingPolicy()));
 
     auto scanActor = ctx.Register(new TColumnShardScan(Self->SelfId(), scanComputeActor, Self->GetStoragesManager(),
-        shardingPolicy, scanId, txId, scanGen, requestCookie, Self->TabletID(), timeout, std::move(ReadMetadataRanges), dataFormat, Self->ScanCounters));
-
-    LOG_S_DEBUG("TTxScan starting " << scanActor
-        << " txId: " << txId
-        << " scanId: " << scanId
-        << " gen: " << scanGen
-        << " table: " << table
-        << " snapshot: " << snapshot
-        << " timeout: " << timeout
-        << detailedInfo.Str()
-        << " at tablet " << Self->TabletID());
+        shardingPolicy, scanId, txId, scanGen, *requestCookie, Self->TabletID(), timeout, ReadMetadataRange, dataFormat, Self->ScanCounters));
+
+    AFL_DEBUG(NKikimrServices::TX_COLUMNSHARD_SCAN)("event", "TTxScan started")("actor_id", scanActor)("trace_detailed", detailedInfo);
 }
 
 }
diff --git a/ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.h b/ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.h
index 36ad75ae47..2d9eb9619a 100644
--- a/ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.h
+++ b/ydb/core/tx/columnshard/engines/reader/transaction/tx_scan.h
@@ -22,7 +22,7 @@ public:
 private:
     TString ErrorDescription;
     TEvColumnShard::TEvScan::TPtr Ev;
-    std::vector<TReadMetadataPtr> ReadMetadataRanges;
+    TReadMetadataPtr ReadMetadataRange;
 };
 
 }
\ No newline at end of file
diff --git a/ydb/core/tx/columnshard/inflight_request_tracker.cpp b/ydb/core/tx/columnshard/inflight_request_tracker.cpp
index bd593dff80..98ca6d7ab6 100644
--- a/ydb/core/tx/columnshard/inflight_request_tracker.cpp
+++ b/ydb/core/tx/columnshard/inflight_request_tracker.cpp
@@ -47,13 +47,13 @@ void TInFlightReadsTracker::RemoveInFlightRequest(ui64 cookie, const NOlap::TVer
     RequestsMeta.erase(cookie);
 }
 
-void TInFlightReadsTracker::AddToInFlightRequest(const ui64 cookie, NOlap::NReader::TReadMetadataBase::TConstPtr readMetaBase, const NOlap::TVersionedIndex* index) {
+TConclusionStatus TInFlightReadsTracker::AddToInFlightRequest(const ui64 cookie, NOlap::NReader::TReadMetadataBase::TConstPtr readMetaBase, const NOlap::TVersionedIndex* index) {
     RequestsMeta[cookie].push_back(readMetaBase);
 
     auto readMeta = std::dynamic_pointer_cast<const NOlap::NReader::NPlain::TReadMetadata>(readMetaBase);
 
     if (!readMeta) {
-        return;
+        return TConclusionStatus::Success();
     }
 
     auto selectInfo = readMeta->SelectInfo;
@@ -69,7 +69,10 @@ void TInFlightReadsTracker::AddToInFlightRequest(const ui64 cookie, NOlap::NRead
     }
 
     for (auto&& i : portionBlobIds) {
-        auto storage = StoragesManager->GetOperatorVerified(i.first);
+        auto storage = StoragesManager->GetOperatorOptional(i.first);
+        if (!storage) {
+            return TConclusionStatus::Fail("blobs storage info not ready for '" + i.first + "'");
+        }
         auto tracker = storage->GetBlobsTracker();
         for (auto& blobId : i.second) {
             tracker->UseBlob(blobId);
@@ -81,6 +84,7 @@ void TInFlightReadsTracker::AddToInFlightRequest(const ui64 cookie, NOlap::NRead
     for (const auto& committedBlob : readMeta->CommittedBlobs) {
         tracker->UseBlob(committedBlob.GetBlobRange().GetBlobId());
     }
+    return TConclusionStatus::Success();
 }
 
 }
diff --git a/ydb/core/tx/columnshard/inflight_request_tracker.h b/ydb/core/tx/columnshard/inflight_request_tracker.h
index 03fc5d7a2a..d530c11d7a 100644
--- a/ydb/core/tx/columnshard/inflight_request_tracker.h
+++ b/ydb/core/tx/columnshard/inflight_request_tracker.h
@@ -14,18 +14,11 @@ using NOlap::IBlobInUseTracker;
 class TInFlightReadsTracker {
 public:
     // Returns a unique cookie associated with this request
-    ui64 AddInFlightRequest(NOlap::NReader::TReadMetadataBase::TConstPtr readMeta, const NOlap::TVersionedIndex* index) {
+    [[nodiscard]] TConclusion<ui64> AddInFlightRequest(NOlap::NReader::TReadMetadataBase::TConstPtr readMeta, const NOlap::TVersionedIndex* index) {
         const ui64 cookie = NextCookie++;
-        AddToInFlightRequest(cookie, readMeta, index);
-        return cookie;
-    }
-
-    // Returns a unique cookie associated with this request
-    template <class TReadMetadataList>
-    ui64 AddInFlightRequest(const TReadMetadataList& readMetaList, const NOlap::TVersionedIndex* index) {
-        const ui64 cookie = NextCookie++;
-        for (const auto& readMetaPtr : readMetaList) {
-            AddToInFlightRequest(cookie, readMetaPtr, index);
+        auto status = AddToInFlightRequest(cookie, readMeta, index);
+        if (!status) {
+            return status;
         }
         return cookie;
     }
@@ -50,7 +43,7 @@ public:
     }
 
 private:
-    void AddToInFlightRequest(const ui64 cookie, NOlap::NReader::TReadMetadataBase::TConstPtr readMetaBase, const NOlap::TVersionedIndex* index);
+    [[nodiscard]] TConclusionStatus AddToInFlightRequest(const ui64 cookie, NOlap::NReader::TReadMetadataBase::TConstPtr readMetaBase, const NOlap::TVersionedIndex* index);
 
 private:
     std::shared_ptr<NOlap::IStoragesManager> StoragesManager;