MB-28753 - document number "xxx" not found

err with update workload

Introducer was incorrectly updating the offsets slice
of segments, by considering only the live doc count
while computing the "running". This can result in
incorrectly computing the residing segment as well as
the local doc numbers while loading a document after
a search hit.

index/scorch/introducer.go

@@ -154,7 +154,7 @@ func (s *Scorch) introduceSegment(next *segmentIntroduction) error {
 			newSnapshot.segment = append(newSnapshot.segment, newss)
 			root.segment[i].segment.AddRef()
 			newSnapshot.offsets = append(newSnapshot.offsets, running)
-			running += root.segment[i].Count()
+			running += newss.segment.Count()
 		}
 	}
 
@@ -315,7 +315,7 @@ func (s *Scorch) introduceMerge(nextMerge *segmentMerge) {
 			})
 			root.segment[i].segment.AddRef()
 			newSnapshot.offsets = append(newSnapshot.offsets, running)
-			running += root.segment[i].Count()
+			running += root.segment[i].segment.Count()
 		}
 	}