avoid decommissioning DEL markers with single versions (#17274)

cmd/erasure-server-pool-decom.go

@@ -673,9 +673,6 @@ func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool
 		return err
 	}
 
-	for _, set := range pool.sets {
-		set := set
-
 	vc, _ := globalBucketVersioningSys.Get(bi.Name)
 
 	// Check if the current bucket has a configured lifecycle policy
@@ -684,6 +681,9 @@ func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool
 	// Check if bucket is object locked.
 	lr, _ := globalBucketObjectLockSys.Get(bi.Name)
 
+	for _, set := range pool.sets {
+		set := set
+
 		filterLifecycle := func(bucket, object string, fi FileInfo) bool {
 			if lc == nil {
 				return false
@@ -728,22 +728,33 @@ func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool
 					continue
 				}
 
+				// any object with only single DEL marker we don't need
+				// to decommission, just skip it.
+				if version.Deleted && len(fivs.Versions) == 1 {
+					decommissionedCount++
+					continue
+				}
+
+				versionID := version.VersionID
+				if versionID == "" {
+					versionID = nullVersionID
+				}
+
 				if version.Deleted {
 					_, err := z.DeleteObject(ctx,
 						bi.Name,
 						version.Name,
 						ObjectOptions{
-							Versioned:          vc.PrefixEnabled(version.Name),
-							VersionID:          version.VersionID,
+							// Since we are preserving a delete marker, we have to make sure this is always true.
+							// regardless of the current configuration of the bucket we must preserve all versions
+							// on the pool being decommissioned.
+							Versioned:          true,
+							VersionID:          versionID,
 							MTime:              version.ModTime,
 							DeleteReplication:  version.ReplicationState,
 							DeleteMarker:       true, // make sure we create a delete marker
 							SkipDecommissioned: true, // make sure we skip the decommissioned pool
 						})
-					if isErrObjectNotFound(err) || isErrVersionNotFound(err) {
-						// object/version already deleted by the application, nothing to do here we move on.
-						continue
-					}
 					var failure bool
 					if err != nil {
 						logger.LogIf(ctx, err)
@@ -765,7 +776,7 @@ func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool
 					if version.IsRemote() {
 						stopFn := globalDecommissionMetrics.log(decomMetricDecommissionObject, idx, bi.Name, version.Name, version.VersionID)
 						if err := z.DecomTieredObject(ctx, bi.Name, version.Name, version, ObjectOptions{
-							VersionID:   version.VersionID,
+							VersionID:   versionID,
 							MTime:       version.ModTime,
 							UserDefined: version.Metadata,
 						}); err != nil {
@@ -785,7 +796,7 @@ func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool
 						nil,
 						http.Header{},
 						ObjectOptions{
-							VersionID:    version.VersionID,
+							VersionID:    versionID,
 							NoDecryption: true,
 							NoLock:       true,
 						})