Class MergeScan

java.lang.Object

org.apache.derby.impl.store.access.sort.Scan

org.apache.derby.impl.store.access.sort.SortScan

org.apache.derby.impl.store.access.sort.MergeScan

All Implemented Interfaces:

ScanManager, GenericScanController, GroupFetchScanController, RowCountable, ScanController, ScanInfo

Direct Known Subclasses:

MergeScanRowSource

public class MergeScan
extends SortScan

A sort scan that is capable of merging as many merge runs as will fit in the passed-in sort buffer.

Field Summary

Fields

Modifier and Type	Field	Description
protected Vector<Long>	mergeRuns	The merge runs.
protected StreamContainerHandle[]	openScans	Array of scan controllers for the merge runs.
protected SortBuffer	sortBuffer	The sort buffer we will use.
private SortObserver	sortObserver

Fields inherited from class SortScan

current, hold, sort, tran

Fields inherited from interface ScanController

GE, GT, NA

Constructor Summary

Constructors

Constructor	Description
MergeScan(MergeSort sort, TransactionManager tran, SortBuffer sortBuffer, Vector<Long> mergeRuns, SortObserver sortObserver, boolean hold)

Method Summary

Modifier and Type	Method	Description
void	close()	Close the scan.
boolean	closeForEndTransaction(boolean closeHeldScan)	Close the scan.
boolean	init(TransactionManager tran)	Initialize the scan, returning false if there was some error.
(package private) void	mergeARow(int scanindex)	Insert rows while we keep getting duplicates from the merge run whose scan is in the open scan array entry indexed by scanindex.
boolean	next()	Move to the next position in the scan.

Methods inherited from class SortScan

fetch, fetchNext, fetchWithoutQualify

Methods inherited from class Scan

delete, didNotQualify, doesCurrentPositionQualify, fetchLocation, fetchNextGroup, fetchNextGroup, fetchSet, getAllScanInfo, getEstimatedRowCount, getScanInfo, isCurrentPositionDeleted, isHeldAfterCommit, isKeyed, isTableLocked, newRowLocationTemplate, positionAtRowLocation, reopenScan, reopenScanByRowLocation, replace, setEstimatedRowCount

Methods inherited from class Object

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

Field Details

sortBuffer

protected SortBuffer sortBuffer

The sort buffer we will use.

mergeRuns

protected Vector<Long> mergeRuns

The merge runs.

openScans

protected StreamContainerHandle[] openScans

Array of scan controllers for the merge runs. Entries in the array become null as the last row is pulled out and the scan is closed.

sortObserver

private SortObserver sortObserver

Constructor Details

MergeScan

MergeScan(MergeSort sort,
 TransactionManager tran,
 SortBuffer sortBuffer,
 Vector<Long> mergeRuns,
 SortObserver sortObserver,
 boolean hold)

Method Details

next

public boolean next()
             throws StandardException

Move to the next position in the scan.

Returns:

True if there is a next position in the scan, false if there isn't.

Throws:

StandardException - Standard exception policy.

See Also:

• ScanController.next()

close

public void close()

Close the scan.

Specified by:

close in interface GenericScanController

Overrides:

close in class SortScan

See Also:

• GenericScanController.close()

closeForEndTransaction

public boolean closeForEndTransaction(boolean closeHeldScan)

Close the scan.

Parameters:

closeHeldScan - If true, means to close scan even if it has been opened to be kept opened across commit. This is used to close these scans on abort.

Returns:

boolean indicating that the close has resulted in a real close of the scan. A held scan will return false if called by closeForEndTransaction(false), otherwise it will return true. A non-held scan will always return true.

See Also:

• ScanManager.closeForEndTransaction(boolean)

init

public boolean init(TransactionManager tran)
             throws StandardException

Initialize the scan, returning false if there was some error.

Throws:

StandardException

mergeARow

void mergeARow(int scanindex)
        throws StandardException

Insert rows while we keep getting duplicates from the merge run whose scan is in the open scan array entry indexed by scanindex.

Throws:

StandardException