amogh-jahagirdar commented on code in PR #15006:
URL: https://github.com/apache/iceberg/pull/15006#discussion_r2678917066


##########
core/src/main/java/org/apache/iceberg/MergingSnapshotProducer.java:
##########
@@ -1063,16 +1112,121 @@ private List<ManifestFile> newDeleteFilesAsManifests() 
{
       newDeleteFilesBySpec.forEach(
           (specId, deleteFiles) -> {
             PartitionSpec spec = ops().current().spec(specId);
+            if (foundDuplicateDVs) {
+              mergeDVsAndUpdateDeleteFiles(deleteFiles, spec);
+            }
+
+            // Update summaries for all delete files including eq. deletes for 
this partition spec
+            deleteFiles.forEach(file -> addedFilesSummary.addedFile(spec, 
file));
+
             List<ManifestFile> newDeleteManifests = 
writeDeleteManifests(deleteFiles, spec);
             cachedNewDeleteManifests.addAll(newDeleteManifests);
           });
 
       this.hasNewDeleteFiles = false;
+      this.foundDuplicateDVs = false;
     }
 
     return cachedNewDeleteManifests;
   }
 
+  private void mergeDVsAndUpdateDeleteFiles(DeleteFileSet deleteFiles, 
PartitionSpec spec) {
+    // Filter out DVs and group them by referenced data file
+    Map<String, List<DeleteFile>> dvsByReferencedLocation =
+        deleteFiles.stream()
+            .filter(ContentFileUtil::isDV)
+            .collect(
+                Collectors.toMap(
+                    DeleteFile::referencedDataFile,
+                    Lists::newArrayList,
+                    (existingDVs, newDVs) -> {
+                      existingDVs.addAll(newDVs);
+                      return existingDVs;
+                    }));
+
+    // Merge DVs
+    Map<String, List<DeleteFile>> dvsThatNeedMerging =
+        dvsByReferencedLocation.entrySet().stream()
+            .filter(e -> e.getValue().size() > 1)
+            .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
+
+    List<DeleteFile> newDVs = Lists.newArrayList();
+    Tasks.foreach(dvsThatNeedMerging.entrySet())
+        .executeWith(ThreadPools.getDeleteWorkerPool())
+        .stopOnFailure()
+        .throwFailureWhenFinished()
+        .run(
+            dvsToMergeForDataFile ->
+                newDVs.add(
+                    mergeAndWriteDV(
+                        dvsToMergeForDataFile.getKey(), 
dvsToMergeForDataFile.getValue(), spec)));
+
+    // Remove the merged DVs from the tracking set
+    for (List<DeleteFile> dvsThatWereMerged : dvsThatNeedMerging.values()) {
+      dvsThatWereMerged.forEach(deleteFiles::remove);
+    }
+
+    // Add the new DVs to the tracking set
+    deleteFiles.addAll(newDVs);
+  }
+
+  private DeleteFile mergeAndWriteDV(
+      String referencedDataFile, List<DeleteFile> dvs, PartitionSpec spec) {
+    DeleteFile firstDV = dvs.get(0);
+    PositionDeleteIndex positionDeleteIndex =
+        Deletes.readDV(firstDV, ops().io(), ops().encryption());
+    for (int i = 1; i < dvs.size(); i++) {
+      DeleteFile dv = dvs.get(i);
+      Preconditions.checkArgument(
+          Objects.equals(dv.dataSequenceNumber(), 
firstDV.dataSequenceNumber()),
+          "Cannot merge duplicate added DVs when data sequence numbers are 
different,"
+              + "expected all to be added with sequence %s, but got %s",

Review Comment:
   Primarily a safety net, because this check is only for the case where 
duplicate DVs are added in a single commit. 
   
   The way I think about it is if someone is adding DVs in a single commit that 
are duplicate AND span multiple sequence numbers, then something is probably 
wrong and from a merging perspective we'll really have no basis for inferring 
what the right sequence number to use is. So, I think it's reasonable to fail 
the commit in this case.



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