Package org.apache.drill.exec.physical.impl.scan.v3.lifecycle

Class ScanEventListener

java.lang.Object

org.apache.drill.exec.physical.impl.scan.v3.lifecycle.ScanEventListener

All Implemented Interfaces:

ScanOperatorEvents

public class ScanEventListener
extends Object
implements ScanOperatorEvents

Binds the scan lifeycle to the scan operator. Defers creating the scan lifecycle until the operator context is available to allow most fields in the scan lifecycle to be immutable.

Constructor Summary

Constructors

Constructor	Description
ScanEventListener(ScanLifecycleBuilder scanOptions)

Method Summary

Modifier and Type	Method	Description
void	bind(OperatorContext context)	Build the scan-level schema from the physical operator select list.
void	close()	Called when the scan operator itself is closed.
RowBatchReader	nextReader()	A scanner typically readers multiple data sources (such as files or file blocks.) A batch reader handles each read.

Methods inherited from class java.lang.Object

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

Constructor Details

ScanEventListener

public ScanEventListener(ScanLifecycleBuilder scanOptions)

Method Details

bind

public void bind(OperatorContext context)

Description copied from interface: ScanOperatorEvents

Build the scan-level schema from the physical operator select list. The operator context is provided to allow access to the user name, to options, and to other information that might influence schema resolution.

After this call, the schema manager should be ready to build a reader-specific schema for each reader as it is opened.

Specified by:

bind in interface ScanOperatorEvents

Parameters:

context - the operator context for the scan operator

nextReader

public RowBatchReader nextReader()

Description copied from interface: ScanOperatorEvents

A scanner typically readers multiple data sources (such as files or file blocks.) A batch reader handles each read. This method returns the next reader in whatever sequence that this scan defines.

The preferred implementation is to create each batch reader in this call to minimize resource usage. Production queries may read thousands of files or blocks, so incremental reader creation can be far more efficient than creating readers at the start of the scan.

Specified by:

nextReader in interface ScanOperatorEvents

Returns:

a batch reader for one of the scan elements within the scan physical plan for this scan operator

close

public void close()

Description copied from interface: ScanOperatorEvents

Called when the scan operator itself is closed. Indicates that no more readers are available.

Specified by:

close in interface ScanOperatorEvents