public CostEstimate costIndexScan(Index index,long nrows){
  return new CostEstimate(nrows,model.indexScan(schema.indexRowType(index),(int)nrows));
}

public CostEstimate costIndexScan ( Index index , long nrows ) { return new CostEstimate ( nrows , model . indexScan ( schema . indexRowType ( index ) , ( int ) nrows ) ) ; }
estimate cost of scanning given number of rows from this index . one random access to get there , then nrows - 1 sequential accesses following , plus a surcharge for copying something as wide as the index .
