org.apache.hadoop.hive.ql.optimizer.stats.annotation
Class StatsRulesProcFactory.SelectStatsRule

java.lang.Object
  org.apache.hadoop.hive.ql.optimizer.stats.annotation.StatsRulesProcFactory.DefaultStatsRule
      org.apache.hadoop.hive.ql.optimizer.stats.annotation.StatsRulesProcFactory.SelectStatsRule

All Implemented Interfaces:

NodeProcessor

Enclosing class:

StatsRulesProcFactory

public static class StatsRulesProcFactory.SelectStatsRule
extends StatsRulesProcFactory.DefaultStatsRule
implements NodeProcessor

SELECT operator doesn't change the number of rows emitted from the parent operator. It changes the size of each tuple emitted. In a typical case, where only subset of columns are selected the average row size will reduce as some of the columns will be pruned. In order to accurately compute the average row size, column level statistics is required. Column level statistics stores average size of values in column which can be used to more reliably estimate the reduction in size of each tuple. In the absence of column level statistics, size of columns will be based on data type. For primitive data types size from JavaDataModel will be used and for variable length data types worst case will be assumed.

For more information, refer 'Estimating The Cost Of Operations' chapter in "Database Systems: The Complete Book" by Garcia-Molina et. al.

Constructor Summary

StatsRulesProcFactory.SelectStatsRule()

Method Summary

Object

process(Node nd, Stack<Node> stack, NodeProcessorCtx procCtx, Object... nodeOutputs) Generic process for all ops that don't have specific implementations.

Methods inherited from class java.lang.Object

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

Constructor Detail

StatsRulesProcFactory.SelectStatsRule

public StatsRulesProcFactory.SelectStatsRule()

Method Detail

process

public Object process(Node nd,
                      Stack<Node> stack,
                      NodeProcessorCtx procCtx,
                      Object... nodeOutputs)
               throws SemanticException

Description copied from interface: NodeProcessor

Generic process for all ops that don't have specific implementations.

Specified by:

process in interface NodeProcessor

Overrides:

process in class StatsRulesProcFactory.DefaultStatsRule

Parameters:

nd - operator to process

procCtx - operator processor context

nodeOutputs - A variable argument list of outputs from other nodes in the walk

Returns:

Object to be returned by the process call

Throws:

SemanticException