YQ-3893 Fix next message offset in topic session (#12284)

Author: kardymonds

ydb/core/fq/libs/row_dispatcher/topic_session.cpp

@@ -148,8 +148,8 @@ class TTopicSession : public TActorBootstrapped<TTopicSession> {
         TQueue<std::pair<ui64, TString>> Buffer;
         ui64 UnreadBytes = 0;
         bool DataArrivedSent = false;
-        TMaybe<ui64> NextMessageOffset;
-        ui64 LastSendedNextMessageOffset = 0;
+        TMaybe<ui64> NextMessageOffset;                 // offset to restart topic session
+        TMaybe<ui64> ProcessedNextMessageOffset;        // offset of fully processed data (to save to checkpoint)
         TVector<ui64> FieldsIds;
         TDuration ReconnectPeriod;
         TStats Stat;        // Send (filtered) to read_actor
@@ -509,16 +509,15 @@ void TTopicSession::Handle(NFq::TEvPrivate::TEvSendStatisticToReadActor::TPtr&)
 
     auto readBytes = ClientsStats.Bytes;
     for (auto& [actorId, info] : Clients) {
-        if (!info.NextMessageOffset) {
+        if (!info.ProcessedNextMessageOffset) {
             continue;
         }
         auto event = std::make_unique<TEvRowDispatcher::TEvStatistics>();
         event->Record.SetPartitionId(PartitionId);
-        event->Record.SetNextMessageOffset(*info.NextMessageOffset);
+        event->Record.SetNextMessageOffset(*info.ProcessedNextMessageOffset);
         event->Record.SetReadBytes(readBytes);
-        info.LastSendedNextMessageOffset = *info.NextMessageOffset;
         event->ReadActorId = info.ReadActorId;
-        LOG_ROW_DISPATCHER_TRACE("Send status to " << info.ReadActorId << ", offset " << *info.NextMessageOffset);
+        LOG_ROW_DISPATCHER_TRACE("Send status to " << info.ReadActorId << ", offset " << info.ProcessedNextMessageOffset);
         Send(RowDispatcherActorId, event.release());
     }
     ClientsStats.Clear();
@@ -541,6 +540,11 @@ void TTopicSession::Handle(NFq::TEvPrivate::TEvDataFiltered::TPtr& ev) {
         if (!info.NextMessageOffset || *info.NextMessageOffset < ev->Get()->Offset + 1) {
             info.NextMessageOffset = ev->Get()->Offset + 1;
         }
+        if (info.Buffer.empty()) {
+            if (!info.ProcessedNextMessageOffset || *info.ProcessedNextMessageOffset < ev->Get()->Offset + 1) {
+                info.ProcessedNextMessageOffset = ev->Get()->Offset + 1;
+            }
+        }
     }
 }
 
@@ -776,7 +780,7 @@ void TTopicSession::SendData(TClientsInfo& info) {
     } while(!info.Buffer.empty());
     info.Stat.Add(dataSize, eventsSize);
     info.FilteredDataRate->Add(dataSize);
-    info.LastSendedNextMessageOffset = *info.NextMessageOffset;
+    info.ProcessedNextMessageOffset = *info.NextMessageOffset;
 }
 
 void TTopicSession::UpdateFieldsIds(TClientsInfo& info) {

ydb/core/fq/libs/row_dispatcher/ut/topic_session_ut.cpp

@@ -206,13 +206,14 @@ class TFixture : public NUnitTest::TBaseFixture {
         return eventHolder->Get()->Record.MessagesSize();
     }
 
-    void ExpectStatisticToReadActor(TSet<NActors::TActorId> readActorIds) {
+    void ExpectStatisticToReadActor(TSet<NActors::TActorId> readActorIds, ui64 expectedNextMessageOffset) {
         size_t count = readActorIds.size();
         for (size_t i = 0; i < count; ++i) {
             auto eventHolder = Runtime.GrabEdgeEvent<TEvRowDispatcher::TEvStatistics>(RowDispatcherActorId, TDuration::Seconds(GrabTimeoutSec));
             UNIT_ASSERT(eventHolder.Get() != nullptr);
             UNIT_ASSERT(readActorIds.contains(eventHolder->Get()->ReadActorId));
             readActorIds.erase(eventHolder->Get()->ReadActorId);
+            UNIT_ASSERT_VALUES_EQUAL(eventHolder->Get()->Record.GetNextMessageOffset(), expectedNextMessageOffset);
         }
     }
 
@@ -244,12 +245,20 @@ Y_UNIT_TEST_SUITE(TopicSessionTests) {
         StartSession(ReadActorId1, source);
         StartSession(ReadActorId2, source);
 
-        const std::vector<TString> data = { Json1 };
+        std::vector<TString> data = { Json1 };
         PQWrite(data, topicName);
         ExpectNewDataArrived({ReadActorId1, ReadActorId2});
         ExpectMessageBatch(ReadActorId1, { Json1 });
         ExpectMessageBatch(ReadActorId2, { Json1 });
-        ExpectStatisticToReadActor({ReadActorId1, ReadActorId2});
+        ExpectStatisticToReadActor({ReadActorId1, ReadActorId2}, 1);
+
+        data = { Json2 };
+        PQWrite(data, topicName);
+        ExpectNewDataArrived({ReadActorId1, ReadActorId2});
+        ExpectStatisticToReadActor({ReadActorId1, ReadActorId2}, 1);
+        ExpectMessageBatch(ReadActorId1, data);
+        ExpectMessageBatch(ReadActorId2, data);
+        ExpectStatisticToReadActor({ReadActorId1, ReadActorId2}, 2);
 
         auto source2 = BuildSource(topicName, false, "OtherConsumer");
         StartSession(ReadActorId3, source2, Nothing(), true);