private FetchData checkOperators(FetchData fetch, boolean aggressive, boolean bypassFilter) {
    if (aggressive) {
      return isConvertible(fetch) ? fetch : null;
    }
    return checkOperators(fetch, fetch.scanOp, bypassFilter);
  }
Tries to convert simple fetch query to single fetch task, which fetches rows directly
from location of table/partition.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/SimpleFetchOptimizer.java