Package edu.caltech.nanodb.queryeval

Class StatisticsUpdater

  • public class StatisticsUpdater
extends java.lang.Object
    This helper class provides basic functionality for updating column statistics based on a selection predicate. The supported predicates are very limited, because the problem becomes very grungy for arbitrary predicates. Supported predicates include:
    • A single comparison between a column and a value
    • A Boolean AND expression, although only the column-value comparisons within the expression will be used to update statistics

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      private StatisticsUpdater()
      This class should not be instantiated.

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      private static void updateCompareStats​(CompareOperator comp, Schema schema, java.util.List<ColumnStats> stats)
      Try to update the column-statistics based on the passed-in comparison operation.
      static java.util.ArrayList<ColumnStats> updateStats​(Expression expr, Schema schema, java.util.List<ColumnStats> inputStats)
      This static helper takes a selection predicate, a schema the predicate is evaluated against, and input column-statistics, and produces output column-statistics that reflect the input arguments.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • StatisticsUpdater

        private StatisticsUpdater()
        This class should not be instantiated.

    • Method Detail

      • updateStats

        public static java.util.ArrayList<ColumnStats> updateStats​(Expression expr,
                                                           Schema schema,
                                                           java.util.List<ColumnStats> inputStats)

        This static helper takes a selection predicate, a schema the predicate is evaluated against, and input column-statistics, and produces output column-statistics that reflect the input arguments. The output is a deep-copy of the input, so that no accidental side-effects occur.

        Only a very limited number of selection predicates are supported, all centering around conjunctive selection based on "COLUMN op VALUE" components. Other kinds of predicates will not be used to update the statistics.

        If a predicate includes a column-reference that is not part of the input schema, then that part of the predicate will be ignored.

        Parameters:
        expr - the selection predicate
        schema - the schema that the selection predicate is evaluated against
        inputStats - the column statistics of the input tuple-sequence that will be filtered by the selection predicate
        Returns:
        estimated column statistics

      • updateCompareStats

        private static void updateCompareStats​(CompareOperator comp,
                                       Schema schema,
                                       java.util.List<ColumnStats> stats)
        Try to update the column-statistics based on the passed-in comparison operation. Updates will only occur if the comparison is of the form "COLUMN = VALUE".
        Parameters:
        comp - The comparison operation to consider
        schema - The schema that the operation is evaluated against
        stats - the statistics to update based on the comparison