Fix partitioning for empty tables (#9372)

Author: fexolm

ydb/core/kqp/ut/olap/blobs_sharing_ut.cpp

@@ -411,7 +411,7 @@ Y_UNIT_TEST_SUITE(KqpOlapBlobsSharing) {
 
     public:
         TAsyncReshardingTest() {
-            TLocalHelper(Kikimr).CreateTestOlapTable("olapTable", "olapStore", 24, 4);
+            TLocalHelper(Kikimr).CreateTestOlapTable("olapTable", "olapStore", 128, 4);
         }
 
         void AddBatch(int numRows) {
@@ -475,6 +475,18 @@ Y_UNIT_TEST_SUITE(KqpOlapBlobsSharing) {
         tester.CheckCount();
     }
 
+    Y_UNIT_TEST(SplitEmpty) {
+        TAsyncReshardingTest tester;
+
+        tester.CheckCount();
+
+        tester.StartResharding("SPLIT");
+
+        tester.CheckCount();
+        tester.WaitResharding();
+        tester.CheckCount();
+    }
+
     Y_UNIT_TEST(ChangeSchemaAndSplit) {
         TAsyncReshardingTest tester;
         tester.DisableCompaction();

ydb/core/tx/columnshard/data_sharing/common/session/common.cpp

@@ -22,13 +22,12 @@ bool TCommonSession::TryStart(const NColumnShard::TColumnShard& shard) {
     THashMap<ui64, std::vector<std::shared_ptr<TPortionInfo>>> portionsByPath;
     THashSet<TString> StoragesIds;
     for (auto&& i : GetPathIdsForStart()) {
-        auto& portionsVector = portionsByPath[i];
         const auto& g = index.GetGranuleVerified(i);
         for (auto&& p : g.GetPortionsOlderThenSnapshot(GetSnapshotBarrier())) {
             if (shard.GetDataLocksManager()->IsLocked(*p.second, { "sharing_session:" + GetSessionId() })) {
                 return false;
             }
-            portionsVector.emplace_back(p.second);
+            portionsByPath[i].emplace_back(p.second);
         }
     }
 
@@ -52,7 +51,7 @@ void TCommonSession::PrepareToStart(const NColumnShard::TColumnShard& shard) {
 }
 
 void TCommonSession::Finish(const NColumnShard::TColumnShard& shard, const std::shared_ptr<NDataLocks::TManager>& dataLocksManager) {
-    AFL_VERIFY(State == EState::InProgress);
+    AFL_VERIFY(State == EState::InProgress || State == EState::Prepared);
     State = EState::Finished;
     shard.GetSharingSessionsManager()->FinishSharingSession();
     AFL_VERIFY(LockGuard);

ydb/core/tx/columnshard/data_sharing/manager/sessions.cpp

@@ -79,6 +79,10 @@ bool TSessionsManager::Load(NTable::TDatabase& database, const TColumnEngineForL
                 AFL_VERIFY(protoSessionCursorStatic->ParseFromString(rowset.GetValue<Schema::SourceSessions::CursorStatic>()));
             }
 
+            if (protoSessionCursorDynamic && !protoSessionCursorStatic) {
+                protoSessionCursorStatic = NKikimrColumnShardDataSharingProto::TSourceSession::TCursorStatic{};
+            }
+
             AFL_VERIFY(index);
             session->DeserializeFromProto(protoSession, protoSessionCursorDynamic, protoSessionCursorStatic).Validate();
             AFL_VERIFY(SourceSessions.emplace(session->GetSessionId(), session).second);

ydb/core/tx/columnshard/data_sharing/source/session/cursor.cpp

@@ -132,8 +132,11 @@ NKikimr::TConclusionStatus TSourceCursor::DeserializeFromProto(const NKikimrColu
     for (auto&& i : protoStatic.GetPathHashes()) {
         PathPortionHashes.emplace(i.GetPathId(), i.GetHash());
     }
-    AFL_VERIFY(PathPortionHashes.size());
-    IsStaticSaved = true;
+    if (PathPortionHashes.empty()) {
+        AFL_ERROR(NKikimrServices::TX_COLUMNSHARD)("problem", "empty static cursor");
+    } else {
+        IsStaticSaved = true;
+    }
     return TConclusionStatus::Success();
 }
 
@@ -178,10 +181,14 @@ bool TSourceCursor::Start(const std::shared_ptr<IStoragesManager>& storagesManag
         local.emplace(i.first, std::move(portionsMap));
     }
     std::swap(PortionsForSend, local);
-    if (!StartPathId) {
-        AFL_VERIFY(PortionsForSend.size());
-        AFL_VERIFY(PortionsForSend.begin()->second.size());
 
+    if (PortionsForSend.empty()) {
+        AFL_VERIFY(!StartPortionId);
+        NextPathId = std::nullopt;
+        NextPortionId = std::nullopt;
+        return true;
+    } else if (!StartPathId) {
+        AFL_VERIFY(PortionsForSend.begin()->second.size());
         NextPathId = PortionsForSend.begin()->first;
         NextPortionId = PortionsForSend.begin()->second.begin()->first;
         AFL_VERIFY(Next(storagesManager, index));