org.apache.hadoop.hbase.client

Class AsyncTableResultScanner

java.lang.Object

org.apache.hadoop.hbase.client.AsyncTableResultScanner

All Implemented Interfaces:

Closeable, AutoCloseable, Iterable<Result>, AdvancedScanResultConsumer, ResultScanner, ScanResultConsumerBase

@InterfaceAudience.Private
class AsyncTableResultScanner
extends Object
implements ResultScanner, AdvancedScanResultConsumer

The ResultScanner implementation for AsyncTable. It will fetch data automatically in background and cache it in memory. Typically the maxCacheSize will be 2 * scan.getMaxResultSize().

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.hadoop.hbase.client.AdvancedScanResultConsumer

AdvancedScanResultConsumer.ScanController, AdvancedScanResultConsumer.ScanResumer

Field Summary

Fields

Modifier and Type	Field and Description
private long	cacheSize
private boolean	closed
private Throwable	error
private static org.slf4j.Logger	LOG
private long	maxCacheSize
private Queue<Result>	queue
private AsyncTable<AdvancedScanResultConsumer>	rawTable
private AdvancedScanResultConsumer.ScanResumer	resumer
private Scan	scan
private ScanMetrics	scanMetrics

Constructor Summary

Constructors

Constructor and Description
AsyncTableResultScanner(AsyncTable<AdvancedScanResultConsumer> table, Scan scan, long maxCacheSize)

Method Summary

Modifier and Type	Method and Description
private void	addToCache(Result result)
void	close() Closes the scanner and releases any resources it has allocated
ScanMetrics	getScanMetrics()
(package private) boolean	isSuspended()
Result	next() Grab the next row's worth of values.
void	onComplete() Indicate that the scan operation is completed normally.
void	onError(Throwable error) Indicate that we hit an unrecoverable error and the scan operation is terminated.
void	onHeartbeat(AdvancedScanResultConsumer.ScanController controller) Indicate that there is a heartbeat message but we have not cumulated enough cells to call AdvancedScanResultConsumer.onNext(Result[], ScanController).
void	onNext(Result[] results, AdvancedScanResultConsumer.ScanController controller) Indicate that we have receive some data.
void	onScanMetricsCreated(ScanMetrics scanMetrics) If scan.isScanMetricsEnabled() returns true, then this method will be called prior to all other methods in this interface to give you the ScanMetrics instance for this scan operation.
boolean	renewLease() Allow the client to renew the scanner's lease on the server.
private void	resumePrefetch()
private void	stopPrefetch(AdvancedScanResultConsumer.ScanController controller)

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.hadoop.hbase.client.ResultScanner

iterator, next

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Field Detail

LOG

private static final org.slf4j.Logger LOG

rawTable

private final AsyncTable<AdvancedScanResultConsumer> rawTable

maxCacheSize

private final long maxCacheSize

scan

private final Scan scan

queue

private final Queue<Result> queue

scanMetrics

private ScanMetrics scanMetrics

cacheSize

private long cacheSize

closed

private boolean closed

error

private Throwable error

resumer

private AdvancedScanResultConsumer.ScanResumer resumer

Constructor Detail

AsyncTableResultScanner

public AsyncTableResultScanner(AsyncTable<AdvancedScanResultConsumer> table,
                               Scan scan,
                               long maxCacheSize)

Method Detail

addToCache

private void addToCache(Result result)

stopPrefetch

private void stopPrefetch(AdvancedScanResultConsumer.ScanController controller)

onNext

public void onNext(Result[] results,
                   AdvancedScanResultConsumer.ScanController controller)

Description copied from interface: AdvancedScanResultConsumer

Indicate that we have receive some data.

Specified by:

onNext in interface AdvancedScanResultConsumer

Parameters:

results - the data fetched from HBase service.

controller - used to suspend or terminate the scan. Notice that the controller instance is only valid within scope of onNext method. You can only call its method in onNext, do NOT store it and call it later outside onNext.

onHeartbeat

public void onHeartbeat(AdvancedScanResultConsumer.ScanController controller)

Description copied from interface: AdvancedScanResultConsumer

Indicate that there is a heartbeat message but we have not cumulated enough cells to call AdvancedScanResultConsumer.onNext(Result[], ScanController).

Note that this method will always be called when RS returns something to us but we do not have enough cells to call AdvancedScanResultConsumer.onNext(Result[], ScanController). Sometimes it may not be a 'heartbeat' message for RS, for example, we have a large row with many cells and size limit is exceeded before sending all the cells for this row. For RS it does send some data to us and the time limit has not been reached, but we can not return the data to client so here we call this method to tell client we have already received something.

This method give you a chance to terminate a slow scan operation.

Specified by:

onHeartbeat in interface AdvancedScanResultConsumer

Parameters:

controller - used to suspend or terminate the scan. Notice that the controller instance is only valid within the scope of onHeartbeat method. You can only call its method in onHeartbeat, do NOT store it and call it later outside onHeartbeat.

onError

public void onError(Throwable error)

Description copied from interface: ScanResultConsumerBase

Indicate that we hit an unrecoverable error and the scan operation is terminated.

We will not call ScanResultConsumerBase.onComplete() after calling ScanResultConsumerBase.onError(Throwable).

Specified by:

onError in interface ScanResultConsumerBase

onComplete

public void onComplete()

Description copied from interface: ScanResultConsumerBase

Indicate that the scan operation is completed normally.

Specified by:

onComplete in interface ScanResultConsumerBase

onScanMetricsCreated

public void onScanMetricsCreated(ScanMetrics scanMetrics)

Description copied from interface: ScanResultConsumerBase

If scan.isScanMetricsEnabled() returns true, then this method will be called prior to all other methods in this interface to give you the ScanMetrics instance for this scan operation. The ScanMetrics instance will be updated on-the-fly during the scan, you can store it somewhere to get the metrics at any time if you want.

Specified by:

onScanMetricsCreated in interface ScanResultConsumerBase

resumePrefetch

private void resumePrefetch()

next

public Result next()
            throws IOException

Description copied from interface: ResultScanner

Grab the next row's worth of values. The scanner will return a Result.

Specified by:

next in interface ResultScanner

Returns:

Result object if there is another row, null if the scanner is exhausted.

Throws:

IOException - e

close

public void close()

Description copied from interface: ResultScanner

Closes the scanner and releases any resources it has allocated

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Specified by:

close in interface ResultScanner

renewLease

public boolean renewLease()

Description copied from interface: ResultScanner

Allow the client to renew the scanner's lease on the server.

Specified by:

renewLease in interface ResultScanner

Returns:

true if the lease was successfully renewed, false otherwise.

isSuspended

boolean isSuspended()

getScanMetrics

public ScanMetrics getScanMetrics()

Specified by:

getScanMetrics in interface ResultScanner

Returns:

the scan metrics, or null if we do not enable metrics.