[Backport stable-25-3-1] PR #30244: Fix S3 data loss in BlobDepot (#30249)

Author: ydbot

ydb/core/blob_depot/data.cpp

@@ -808,6 +808,7 @@ namespace NKikimr::NBlobDepot {
     }
 
     bool TData::IsUseful(const TS3Locator& locator) const {
+        Y_DEBUG_ABORT_UNLESS(IsLoaded());
         return RefCountS3.contains(locator);
     }
 

ydb/core/blob_depot/data_load.cpp

@@ -204,6 +204,7 @@ namespace NKikimr::NBlobDepot {
 
     void TBlobDepot::OnDataLoadComplete() {
         BarrierServer->OnDataLoaded();
+        S3Manager->OnDataLoaded();
         StartGroupAssimilator();
         TabletCounters->Simple()[NKikimrBlobDepot::COUNTER_MODE_LOADING_KEYS] = 0;
         TabletCounters->Simple()[NKikimrBlobDepot::COUNTER_MODE_LOADED] = 1;

ydb/core/blob_depot/s3.cpp

@@ -21,10 +21,11 @@ namespace NKikimr::NBlobDepot {
             Bucket = settings->GetSettings().GetBucket();
             SyncMode = settings->HasSyncMode();
             AsyncMode = settings->HasAsyncMode();
-            RunScannerActor();
+            Enabled = true;
         } else {
             SyncMode = false;
             AsyncMode = false;
+            Enabled = false;
         }
     }
 
@@ -47,6 +48,12 @@ namespace NKikimr::NBlobDepot {
         )
     }
 
+    void TS3Manager::OnDataLoaded() {
+        if (Enabled) {
+            RunScannerActor();
+        }
+    }
+
     void TBlobDepot::InitS3Manager() {
         S3Manager->Init(Config.HasS3BackendSettings() ? &Config.GetS3BackendSettings() : nullptr);
     }

ydb/core/blob_depot/s3.h

@@ -13,6 +13,7 @@ namespace NKikimr::NBlobDepot {
         TString BasePath;
         TString Bucket;
 
+        bool Enabled = false;
         bool SyncMode = false;
         bool AsyncMode = false;
 
@@ -38,6 +39,8 @@ namespace NKikimr::NBlobDepot {
         ui64 GetTotalS3TrashObjects() const { return TotalS3TrashObjects; }
         ui64 GetTotalS3TrashSize() const { return TotalS3TrashSize; }
 
+        void OnDataLoaded();
+
     private: ///////////////////////////////////////////////////////////////////////////////////////////////////////////
         class TTxPrepareWriteS3;
         friend class TBlobDepot;

ydb/core/blob_depot/s3_windows_stub.cpp

@@ -43,6 +43,8 @@ namespace NKikimr::NBlobDepot {
         Y_ABORT("S3 is not supported on Windows");
     }
 
+    void TBlobDepot::OnDataLoaded() {}
+
     void TBlobDepot::InitS3Manager() {
         S3Manager->Init(Config.HasS3BackendSettings() ? &Config.GetS3BackendSettings() : nullptr);
     }