Package org.apache.drill.exec.store.image

Class ImageBatchReader

java.lang.Object

org.apache.drill.exec.store.image.ImageBatchReader

All Implemented Interfaces:

ManagedReader<FileScanFramework.FileSchemaNegotiator>

public class ImageBatchReader
extends Object
implements ManagedReader<FileScanFramework.FileSchemaNegotiator>

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected static class	ImageBatchReader.ColumnDefn	The class mainly process schema definition, index binding, and set up the vector (Column Writers) values.
protected static class	ImageBatchReader.GenericColumnDefn	Responsible for process of the image GenericMetadataDirectory metadata and create data type based on different tags.
protected static class	ImageBatchReader.ListColumnDefn	Responsible for process of the list-map with array writer.
protected static class	ImageBatchReader.MapColumnDefn	Responsible for process of the map writer (nested structure).

Constructor Summary

Constructors

Constructor	Description
ImageBatchReader(ImageFormatConfig config, EasySubScan scan)

Method Summary

Modifier and Type	Method	Description
void	close()	Release resources.
boolean	next()	Read the next batch.
boolean	open(FileScanFramework.FileSchemaNegotiator negotiator)	Setup the record reader.

Methods inherited from class java.lang.Object

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

Constructor Details

ImageBatchReader

public ImageBatchReader(ImageFormatConfig config,
 EasySubScan scan)

Method Details

open

public boolean open(FileScanFramework.FileSchemaNegotiator negotiator)

Description copied from interface: ManagedReader

Setup the record reader. Called just before the first call to next(). Allocate resources here, not in the constructor. Example: open files, allocate buffers, etc.

Specified by:

open in interface ManagedReader<FileScanFramework.FileSchemaNegotiator>

Parameters:

negotiator - mechanism to negotiate select and table schemas, then create the row set reader used to load data into value vectors

Returns:

true if the reader is open and ready to read (possibly no) rows. false for a "soft" failure in which no schema or data is available, but the scanner should not fail, it should move onto another reader

next

public boolean next()

Description copied from interface: ManagedReader

Read the next batch. Reading continues until either EOF, or until the mutator indicates that the batch is full. The batch is considered valid if it is non-empty. Returning true with an empty batch is valid, and is helpful on the very first batch (returning schema only.) An empty batch with a false return code indicates EOF and the batch will be discarded. A non-empty batch along with a false return result indicates a final, valid batch, but that EOF was reached and no more data is available.

This somewhat complex protocol avoids the need to allocate a final batch just to find out that no more data is available; it allows EOF to be returned along with the final batch.

Specified by:

next in interface ManagedReader<FileScanFramework.FileSchemaNegotiator>

Returns:

true if more data may be available (and so next() should be called again, false to indicate that EOF was reached

close

public void close()

Description copied from interface: ManagedReader

Release resources. Called just after a failure, when the scanner is cancelled, or after next() returns EOF. Release all resources and close files. Guaranteed to be called if open() returns normally; will not be called if open() throws an exception.

Specified by:

close in interface ManagedReader<FileScanFramework.FileSchemaNegotiator>