More confident DS proxy phantom blob checking logic (#8611)

Author: alexvru

ydb/core/blobstorage/dsproxy/dsproxy_get_impl.cpp

@@ -57,7 +57,7 @@ void TGetImpl::PrepareReply(NKikimrProto::EReplyStatus status, TString errorReas
 
                 // extra validation code for phantom logic
                 if (PhantomCheck) {
-                    TSubgroupPartLayout possiblyWritten;
+                    TSubgroupPartLayout possiblyPresent;
 
                     for (ui32 idxInSubgroup = 0; idxInSubgroup < blobState.Disks.size(); ++idxInSubgroup) {
                         const auto& disk = blobState.Disks[idxInSubgroup];
@@ -81,10 +81,13 @@ void TGetImpl::PrepareReply(NKikimrProto::EReplyStatus status, TString errorReas
                             }
                             switch (disk.DiskParts[partIdx].Situation) {
                                 case TBlobState::ESituation::Unknown:
+                                    Y_DEBUG_ABORT_S("proxy didn't probe some valid parts of the blob while returning NODATA"
+                                        << " State# " << blobState.ToString());
+                                    [[fallthrough]];
                                 case TBlobState::ESituation::Error:
                                 case TBlobState::ESituation::Present:
                                 case TBlobState::ESituation::Sent:
-                                    possiblyWritten.AddItem(idxInSubgroup, partIdx, Info->Type);
+                                    possiblyPresent.AddItem(idxInSubgroup, partIdx, Info->Type);
                                     break;
 
                                 case TBlobState::ESituation::Absent:
@@ -95,32 +98,11 @@ void TGetImpl::PrepareReply(NKikimrProto::EReplyStatus status, TString errorReas
                         }
                     }
 
-                    switch (Info->Type.GetErasure()) {
-                        case TBlobStorageGroupType::ErasureMirror3dc:
-                            if (possiblyWritten.GetDisksWithPart(0) || possiblyWritten.GetDisksWithPart(1) ||
-                                    possiblyWritten.GetDisksWithPart(2)) {
-                                okay = false;
-                            }
-                            break;
-
-                        case TBlobStorageGroupType::ErasureMirror3of4:
-                            if (possiblyWritten.GetDisksWithPart(0) || possiblyWritten.GetDisksWithPart(1)) {
-                                okay = false;
-                            }
-                            break;
-
-                        default: {
-                            ui32 numDistinctParts = 0;
-                            for (ui32 partIdx = 0; partIdx < Info->Type.TotalPartCount(); ++partIdx) {
-                                if (possiblyWritten.GetDisksWithPart(partIdx)) {
-                                    ++numDistinctParts;
-                                }
-                            }
-                            if (numDistinctParts >= Info->Type.MinimalRestorablePartCount()) {
-                                okay = false;
-                            }
-                            break;
-                        }
+                    const TBlobStorageGroupInfo::TSubgroupVDisks zero(&Info->GetTopology());
+                    const auto& checker = Info->GetQuorumChecker();
+                    const bool canBeRestored = checker.GetBlobState(possiblyPresent, zero) != TBlobStorageGroupInfo::EBS_UNRECOVERABLE_FRAGMENTARY;
+                    if (canBeRestored) {
+                        okay = false; // there is a slight chance that we can restore that blob
                     }
                 }