org.apache.hadoop.hbase.client

Interface RawScanResultConsumer

@InterfaceAudience.Public
public interface RawScanResultConsumer

Receives Result for an asynchronous scan.

Notice that, the onNext(Result[], ScanController) method will be called in the thread which we send request to HBase service. So if you want the asynchronous scanner fetch data from HBase in background while you process the returned data, you need to move the processing work to another thread to make the onNext call return immediately. And please do NOT do any time consuming tasks in all methods below unless you know what you are doing.

Since:

2.0.0

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	RawScanResultConsumer.ScanController Used to suspend or stop a scan, or get a scan cursor if available.
static interface	RawScanResultConsumer.ScanResumer Used to resume a scan.

Method Summary

Modifier and Type	Method and Description
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.
default void	onHeartbeat(RawScanResultConsumer.ScanController controller) Indicate that there is a heartbeat message but we have not cumulated enough cells to call onNext(Result[], ScanController).
void	onNext(Result[] results, RawScanResultConsumer.ScanController controller) Indicate that we have receive some data.
default 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.

Method Detail

onNext

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

Indicate that we have receive some data.

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

default void onHeartbeat(RawScanResultConsumer.ScanController controller)

Indicate that there is a heartbeat message but we have not cumulated enough cells to call 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 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.

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

void onError(Throwable error)

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

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

onComplete

void onComplete()

Indicate that the scan operation is completed normally.

onScanMetricsCreated

default 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. 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.