24-3-9-hotfix: Do not lose ScanShards when altering

ydb/core/tx/schemeshard/schemeshard__operation_alter_cdc_stream.cpp

@@ -61,7 +61,7 @@ class TPropose: public TSubOperationState {
         NIceDb::TNiceDb db(context.GetDB());
 
         context.SS->PersistCdcStream(db, pathId);
-        context.SS->CdcStreams[pathId] = stream->AlterData;
+        context.SS->CdcStreams[pathId]->FinishAlter();
 
         context.SS->ClearDescribePathCaches(path);
         context.OnComplete.PublishToSchemeBoard(OperationId, pathId);

ydb/core/tx/schemeshard/schemeshard_info_types.h

@@ -2437,6 +2437,20 @@ struct TCdcStreamInfo : public TSimpleRefCount<TCdcStreamInfo> {
         return result;
     }
 
+    void FinishAlter() {
+        Y_ABORT_UNLESS(AlterData);
+
+        AlterVersion = AlterData->AlterVersion;
+        Mode = AlterData->Mode;
+        Format = AlterData->Format;
+        VirtualTimestamps = AlterData->VirtualTimestamps;
+        ResolvedTimestamps = AlterData->ResolvedTimestamps;
+        AwsRegion = AlterData->AwsRegion;
+        State = AlterData->State;
+
+        AlterData.Reset();
+    }
+
     ui64 AlterVersion = 1;
     EMode Mode;
     EFormat Format;

ydb/core/tx/schemeshard/ut_cdc_stream/ut_cdc_stream.cpp

@@ -1,7 +1,9 @@
 #include <ydb/core/metering/metering.h>
+#include <ydb/core/testlib/actors/block_events.h>
 #include <ydb/core/tx/schemeshard/ut_helpers/helpers.h>
 #include <ydb/core/tx/schemeshard/schemeshard_billing_helpers.h>
 #include <ydb/core/tx/schemeshard/schemeshard_impl.h>
+#include <ydb/core/tx/schemeshard/schemeshard_private.h>
 
 #include <library/cpp/json/json_reader.h>
 #include <library/cpp/json/json_writer.h>
@@ -1754,6 +1756,80 @@ Y_UNIT_TEST_SUITE(TCdcStreamWithInitialScanTests) {
         env.TestWaitNotification(runtime, txId);
     }
 
+    Y_UNIT_TEST(RacyAlterStreamAndRestart) {
+        TTestBasicRuntime runtime;
+        TTestEnv env(runtime, TTestEnvOptions()
+            .EnableChangefeedInitialScan(true));
+        ui64 txId = 100;
+
+        TActorId schemeShardActorId;
+        auto findActorId = runtime.AddObserver<TEvSchemeShard::TEvModifySchemeTransactionResult>([&](auto& ev) {
+            if (!schemeShardActorId) {
+                schemeShardActorId = ev->Sender;
+            }
+        });
+
+        TestCreateTable(runtime, ++txId, "/MyRoot", R"(
+            Name: "Table"
+            Columns { Name: "key" Type: "Uint64" }
+            Columns { Name: "value" Type: "Uint64" }
+            KeyColumnNames: ["key"]
+        )");
+        env.TestWaitNotification(runtime, txId);
+
+        TBlockEvents<TEvSchemeShard::TEvModifySchemeTransaction> blockedAlterStream(runtime, [&](auto& ev) {
+            const auto& record = ev->Get()->Record;
+            if (record.GetTransaction(0).GetOperationType() == NKikimrSchemeOp::ESchemeOpAlterCdcStream) {
+                txId = record.GetTxId();
+                return true;
+            }
+            return false;
+        });
+
+        TestCreateCdcStream(runtime, ++txId, "/MyRoot", R"(
+            TableName: "Table"
+            StreamDescription {
+              Name: "Stream"
+              Mode: ECdcStreamModeKeysOnly
+              Format: ECdcStreamFormatProto
+              State: ECdcStreamStateScan
+            }
+        )");
+        env.TestWaitNotification(runtime, txId);
+
+        runtime.WaitFor("AlterCdcStream", [&]{ return blockedAlterStream.size(); });
+        blockedAlterStream.Stop();
+
+        UNIT_ASSERT(schemeShardActorId);
+
+        TBlockEvents<TEvPrivate::TEvProgressOperation> blockedProgress(runtime, [&](auto& ev) {
+            return schemeShardActorId == ev->Sender;
+        });
+
+        blockedAlterStream.Unblock();
+        runtime.WaitFor("Progress", [&]{ return blockedProgress.size(); });
+        blockedProgress.Stop();
+
+        RebootTablet(runtime, TTestTxConfig::SchemeShard, runtime.AllocateEdgeActor());
+        env.TestWaitNotification(runtime, txId);
+
+        TestDescribeResult(DescribePrivatePath(runtime, "/MyRoot/Table/Stream"), {
+            NLs::PathExist,
+            NLs::StreamState(NKikimrSchemeOp::ECdcStreamStateReady),
+        });
+
+        TestDropCdcStream(runtime, ++txId, "/MyRoot", R"(
+            TableName: "Table"
+            StreamName: "Stream"
+        )");
+        env.TestWaitNotification(runtime, txId);
+
+        RebootTablet(runtime, TTestTxConfig::SchemeShard, runtime.AllocateEdgeActor());
+        TestDescribeResult(DescribePrivatePath(runtime, "/MyRoot/Table/Stream"), {
+            NLs::PathNotExist,
+        });
+    }
+
     void Metering(bool serverless) {
         TTestBasicRuntime runtime;
         TTestEnv env(runtime, TTestEnvOptions()