org.apache.pig
Interface Algebraic

All Known Implementing Classes:
AVG, COUNT, MAX, MIN, SUM

public interface Algebraic

Suppose we have to compute an function f over a bag X. In general, we need to know the entire X before we can make any progress on f. However, some functions are algebraic e.g. SUM. In these cases, you can apply some initital function f_init on subsets of X to get partial results. You can then combine partial results from different subsets of X using an intermediate function f_intermed. To get the final answers, several partial results can be combined by invoking a final f_final function. For the function SUM, f_init, f_intermed, and f_final are all SUM. See the code for builtin AVG to get a better idea of how algebraic works. When eval functions implement this interface, it is a hint to the system to try and compute partial results early which causes queries to run faster.

Author:
utkarsh

Method Summary
 String getFinal()
           
 String getInitial()
           
 String getIntermed()
           
 

Method Detail

getInitial

String getInitial()
Returns:
A string to instatiate f_init. f_init should be an eval func

getIntermed

String getIntermed()
Returns:
A string to instantiate f_intermed. f_intermed should be an eval func

getFinal

String getFinal()
Returns:
A string to instantiate f_final. f_final should be an eval func parametrized by the same datum as the eval func implementing this interface


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