org.apache.hawq.pxf.service

Class ReadSamplingBridge

java.lang.Object

org.apache.hawq.pxf.service.ReadSamplingBridge

All Implemented Interfaces:

Bridge

public class ReadSamplingBridge
extends java.lang.Object
implements Bridge

ReadSamplingBridge wraps a ReadBridge, and returns only some of the output records, based on a ratio sample. The sample to pass or discard a record is done after all of the processing is completed ( accessor -> resolver -> output builder) to make sure there are no chunks of data instead of single records.
The goal is to get as uniform as possible sampling. This is achieved by creating a bit map matching the precision of the sampleRatio, so that for a ratio of 0.034, a bit-map of 1000 bits will be created, and 34 bits will be set. This map is matched against each read record, discarding ones with a 0 bit and continuing until a 1 bit record is read.

Constructor Summary

Constructors

Constructor and Description
ReadSamplingBridge(ProtocolData protData) C'tor - set the implementation of the bridge.

Method Summary

Modifier and Type	Method and Description
boolean	beginIteration()
Writable	getNext() Fetches next sample, according to the sampling ratio.
boolean	isThreadSafe()
boolean	setNext(java.io.DataInputStream inputStream)

Methods inherited from class java.lang.Object

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

Constructor Detail

ReadSamplingBridge

public ReadSamplingBridge(ProtocolData protData)
                   throws java.lang.Exception

C'tor - set the implementation of the bridge.

Parameters:

protData - input containing sampling ratio

Throws:

java.lang.Exception - if the sampling ratio is wrong

Method Detail

getNext

public Writable getNext()
                 throws java.lang.Exception

Fetches next sample, according to the sampling ratio.

Specified by:

getNext in interface Bridge

Throws:

java.lang.Exception

beginIteration

public boolean beginIteration()
                       throws java.lang.Exception

Specified by:

beginIteration in interface Bridge

Throws:

java.lang.Exception

setNext

public boolean setNext(java.io.DataInputStream inputStream)
                throws java.lang.Exception

Specified by:

setNext in interface Bridge

Throws:

java.lang.Exception

isThreadSafe

public boolean isThreadSafe()

Specified by:

isThreadSafe in interface Bridge