private void updateDeleteTombstoneStats(Collection<IndexFinalState> indexFinalStates) {
    DeleteTombstoneStats.Builder builder = new DeleteTombstoneStats.Builder(time);
    for (IndexFinalState finalState : indexFinalStates) {
      if (finalState.isDelete()) {
        if (finalState.getExpirationTime() != Utils.Infinite_Time) {
          builder.expiredCountInc().expiredSizeInc(finalState.getRecordSize());
        } else {
          builder.permanentCountInc().permanentSizeInc(finalState.getRecordSize(), finalState.getOperationTime());
        }
      }
    }
    deleteTombstoneStats.set(builder.build());
  }
A helper method to update stats for both expired and permanent delete tombstones.
@param indexFinalStates a collection of {@link IndexFinalState} containing DELETE tombstone index value only
ambry-store/src/main/java/com/github/ambry/store/BlobStoreStats.java