org.apache.tajo.storage

Class NullScanner

java.lang.Object

org.apache.tajo.storage.NullScanner

All Implemented Interfaces:

Closeable, AutoCloseable, SchemaObject, Scanner

public class NullScanner
extends Object
implements Scanner

Field Summary

Fields

Modifier and Type	Field and Description
protected int	columnNum
protected org.apache.hadoop.conf.Configuration	conf
protected Fragment	fragment
protected TableMeta	meta
protected float	progress
protected Schema	schema
protected TableStats	tableStats
protected Column[]	targets

Constructor Summary

Constructors

Constructor and Description
NullScanner(org.apache.hadoop.conf.Configuration conf, Schema schema, TableMeta meta, Fragment fragment)

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Close scanner
TableStats	getInputStats()
float	getProgress() How much of the input has the Scanner consumed
Schema	getSchema()
void	init()
boolean	isProjectable() It returns if the projection is executed in the underlying scanner layer.
boolean	isSelectable() It returns if the selection is executed in the underlying scanner layer.
boolean	isSplittable() It returns if the file is splittable.
Tuple	next() It returns one tuple at each call.
void	pushOperators(LogicalNode planPart) Push a plan part into scanner.
void	reset() Reset the cursor.
void	setFilter(EvalNode filter) Set a filter condition
void	setLimit(long num) This method does not guarantee that the scanner will retrieve the specified number of rows.
void	setTarget(Column[] targets) Set target columns

Methods inherited from class java.lang.Object

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

Field Detail

conf

protected final org.apache.hadoop.conf.Configuration conf

meta

protected final TableMeta meta

schema

protected final Schema schema

fragment

protected final Fragment fragment

columnNum

protected final int columnNum

targets

protected Column[] targets

progress

protected float progress

tableStats

protected TableStats tableStats

Constructor Detail

NullScanner

public NullScanner(org.apache.hadoop.conf.Configuration conf,
           Schema schema,
           TableMeta meta,
           Fragment fragment)

Method Detail

init

public void init()
          throws IOException

Specified by:

init in interface Scanner

Throws:

IOException

next

public Tuple next()
           throws IOException

Description copied from interface: Scanner

It returns one tuple at each call.

Specified by:

next in interface Scanner

Returns:

retrieve null if the scanner has no more tuples. Otherwise it returns one tuple.

Throws:

IOException - if internal I/O error occurs during next method

reset

public void reset()
           throws IOException

Description copied from interface: Scanner

Reset the cursor. After executed, the scanner will retrieve the first tuple.

Specified by:

reset in interface Scanner

Throws:

IOException - if internal I/O error occurs during reset method

close

public void close()
           throws IOException

Description copied from interface: Scanner

Close scanner

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Scanner

Throws:

IOException - if internal I/O error occurs during close method

pushOperators

public void pushOperators(LogicalNode planPart)

Description copied from interface: Scanner

Push a plan part into scanner. It will be used in future issues.

Specified by:

pushOperators in interface Scanner

isProjectable

public boolean isProjectable()

Description copied from interface: Scanner

It returns if the projection is executed in the underlying scanner layer. If TRUE, the upper layers (i.e., SeqScanExec) assume that next() will return a tuple which contains only projected fields. In other words, the field number of a retrieved tuple is equivalent tothe number of targets. If FALSE, the upper layers assume that next() will return a tuple which contains projected fields and non-projected fields, padded by NullDatum. In other words, the width of tuple is equivalent to the field number of the table schema.

Specified by:

isProjectable in interface Scanner

Returns:

true if this scanner can project the given columns.

setTarget

public void setTarget(Column[] targets)

Description copied from interface: Scanner

Set target columns

Specified by:

setTarget in interface Scanner

Parameters:

targets - columns to be projected

isSelectable

public boolean isSelectable()

Description copied from interface: Scanner

It returns if the selection is executed in the underlying scanner layer.

Specified by:

isSelectable in interface Scanner

Returns:

true if this scanner can filter tuples against a given condition.

setFilter

public void setFilter(EvalNode filter)

Description copied from interface: Scanner

Set a filter condition

Specified by:

setFilter in interface Scanner

Parameters:

filter - to be searched TODO - to be changed Object type

setLimit

public void setLimit(long num)

Description copied from interface: Scanner

This method does not guarantee that the scanner will retrieve the specified number of rows. This information is used for a hint.

Specified by:

setLimit in interface Scanner

Parameters:

num - The number of rows to be retrieved.

isSplittable

public boolean isSplittable()

Description copied from interface: Scanner

It returns if the file is splittable.

Specified by:

isSplittable in interface Scanner

Returns:

true if this scanner can split the a file.

getProgress

public float getProgress()

Description copied from interface: Scanner

How much of the input has the Scanner consumed

Specified by:

getProgress in interface Scanner

Returns:

progress from 0.0 to 1.0.

getInputStats

public TableStats getInputStats()

Specified by:

getInputStats in interface Scanner

getSchema

public Schema getSchema()

Specified by:

getSchema in interface SchemaObject