Fix VDisk compaction bug (#16151)

Author: alexvru

ydb/core/blobstorage/vdisk/hullop/blobstorage_buildslice.h

@@ -78,18 +78,6 @@ namespace NKikimr {
         // create a new slice
         TLevelSlicePtr res(new TLevelSlice(settings, slice->Ctx));
 
-        // assign VolatileOrderId for any new SSTables at level 0 to allow merging them to level 0 below
-        {
-            for (auto it = addIt; it.Valid(); it.Next()) {
-                if (const auto& table = it.Get(); !table.Level) {
-                    const ui64 prev = std::exchange(table.SstPtr->VolatileOrderId, ++slice->Ctx->VolatileOrderId);
-                    Y_ABORT_UNLESS(prev == 0);
-                } else { // items are sorted in ascending order of Level
-                    break;
-                }
-            }
-        }
-
         ui32 levelsSize = slice->SortedLevels.size();
         if (ctask.Action == NHullComp::ActCompactSsts) {
             Y_ABORT_UNLESS(ctask.CompactSsts.TargetLevel != (ui32)-1);

ydb/core/blobstorage/vdisk/hullop/blobstorage_hullactor.cpp

@@ -480,6 +480,15 @@ namespace NKikimr {
             } else {
                 Y_ABORT_UNLESS(RTCtx->LevelIndex->GetCompState() == TLevelIndexBase::StateCompInProgress);
 
+                // assign VolatileOrderId for any new SSTables at level 0 to allow merging them to level 0 below
+                if (const auto& cs = CompactionTask->CompactSsts; cs.TargetLevel == 0) {
+                    for (auto& seg : msg->SegVec->Segments) {
+                        const ui64 prev = std::exchange(seg->VolatileOrderId,
+                            ++RTCtx->LevelIndex->CurSlice->Ctx->VolatileOrderId);
+                        Y_ABORT_UNLESS(prev == 0);
+                    }
+                }
+
                 CompactionTask->CompactSsts.CompactionFinished(std::move(msg->SegVec),
                     std::move(msg->FreedHugeBlobs), std::move(msg->AllocatedHugeBlobs), msg->Aborted);