code: private Map<CellName, Row> rows(DecoratedKey partitionKey, List<CellName> clusteringKeys, long timestamp) {
          ColumnSlice[] slices = rowMapper.columnSlices(clusteringKeys);
  
          if (baseCfs.metadata.hasStaticColumns()) {
              LinkedList<ColumnSlice> l = new LinkedList<>(Arrays.asList(slices));
              l.addFirst(baseCfs.metadata.comparator.staticPrefix().slice());
              slices = new ColumnSlice[l.size()];
              slices = l.toArray(slices);
          }
  
          SliceQueryFilter dataFilter = new SliceQueryFilter(slices,
                                                             false,
                                                             Integer.MAX_VALUE,
                                                             baseCfs.metadata.clusteringColumns().size());
          QueryFilter queryFilter = new QueryFilter(partitionKey, baseCfs.name, dataFilter, timestamp);
  
          ColumnFamily queryColumnFamily = baseCfs.getColumnFamily(queryFilter);
  
          // Avoid null
          if (queryColumnFamily == null) {
              return null;
          }
  
          // Remove deleted/expired columns
          ColumnFamily cleanQueryColumnFamily = cleanExpired(queryColumnFamily, timestamp);
  
          // Split CQL3 row column families
          Map<CellName, ColumnFamily> columnFamilies = rowMapper.splitRows(cleanQueryColumnFamily);
  
          // Build and return rows
          Map<CellName, Row> rows = new HashMap<>(columnFamilies.size());
          for (Map.Entry<CellName, ColumnFamily> entry : columnFamilies.entrySet()) {
              Row row = new Row(partitionKey, entry.getValue());
              rows.put(entry.getKey(), row);
          }
          return rows;
      }
docs: Returns the CQL3 {@link Row} identified by the specified key pair, using the specified time stamp to ignore
  deleted columns. The {@link Row} is retrieved from the storage engine, so it involves IO operations.
  
  @param partitionKey   The partition key.
  @param clusteringKeys The clustering keys.
  @param timestamp      The time stamp to ignore deleted columns.
  @return The CQL3 {@link Row} identified by the specified key pair.