MergeScan (Apache Derby V10.14 Internals)

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 java.util.Vector<java.lang.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 interface org.apache.derby.iapi.store.access.ScanController
GE, GT, NA

Fields inherited from class org.apache.derby.impl.store.access.sort.SortScan
current, hold, sort, tran

Constructor Summary

Constructors
Constructor	Description
`MergeScan(MergeSort sort, TransactionManager tran, SortBuffer sortBuffer, java.util.Vector<java.lang.Long> mergeRuns, SortObserver sortObserver, boolean hold)`

Method Summary

All Methods Instance Methods Concrete Methods
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 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from class org.apache.derby.impl.store.access.sort.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 org.apache.derby.impl.store.access.sort.SortScan
fetch, fetchNext, fetchWithoutQualify

- Field Detail
  - sortBuffer
```
protected SortBuffer sortBuffer
```
    The sort buffer we will use.
  - mergeRuns
```
protected java.util.Vector<java.lang.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 Detail
  - MergeScan
```
MergeScan(MergeSort sort,
          TransactionManager tran,
          SortBuffer sortBuffer,
          java.util.Vector<java.lang.Long> mergeRuns,
          SortObserver sortObserver,
          boolean hold)
```
- Method Detail
  - 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

Class MergeScan

Field Summary

Fields inherited from interface org.apache.derby.iapi.store.access.ScanController

Fields inherited from class org.apache.derby.impl.store.access.sort.SortScan

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from class org.apache.derby.impl.store.access.sort.Scan

Methods inherited from class org.apache.derby.impl.store.access.sort.SortScan

Field Detail

sortBuffer

mergeRuns

openScans

sortObserver

Constructor Detail

MergeScan

Method Detail

next

close

closeForEndTransaction

init

mergeARow