org.apache.tajo.storage

Interface Scanner

All Superinterfaces:

AutoCloseable, Closeable, SchemaObject

All Known Subinterfaces:

SeekableScanner

All Known Implementing Classes:

AbstractScanner, MergeScanner, NullScanner

public interface Scanner
extends SchemaObject, Closeable

Scanner Interface

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
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 interface org.apache.tajo.catalog.SchemaObject

getSchema

Method Detail

init

void init()
          throws IOException

Throws:

IOException

next

Tuple next()
           throws IOException

It returns one tuple at each call.

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

void reset()
           throws IOException

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

Throws:

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

close

void close()
           throws IOException

Close scanner

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

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

pushOperators

void pushOperators(LogicalNode planPart)

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

Parameters:

planPart -

isProjectable

boolean isProjectable()

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.

Returns:

true if this scanner can project the given columns.

setTarget

void setTarget(Column[] targets)

Set target columns

Parameters:

targets - columns to be projected

isSelectable

boolean isSelectable()

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

Returns:

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

setFilter

void setFilter(EvalNode filter)

Set a filter condition

Parameters:

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

setLimit

void setLimit(long num)

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

Parameters:

num - The number of rows to be retrieved.

isSplittable

boolean isSplittable()

It returns if the file is splittable.

Returns:

true if this scanner can split the a file.

getProgress

float getProgress()

How much of the input has the Scanner consumed

Returns:

progress from 0.0 to 1.0.

getInputStats

TableStats getInputStats()