CardinalityCounter (Apache Derby V10.10 Internals)

java.lang.Object
- org.apache.derby.impl.sql.execute.CardinalityCounter

All Implemented Interfaces:

RowLocationRetRowSource, RowSource
```
public class CardinalityCounter
extends java.lang.Object
implements RowLocationRetRowSource
```
This is a decorator (in Design Patterns Terminology) class to enhance the functionality of a RowLocationRetRowSource. It assumes that the rows are coming in sorted order from the row source and it simply keeps track of the cardinality of all the leading columns.

Field Summary

Fields
Modifier and Type Field and Description

private long[] cardinality

private long numRows

private DataValueDescriptor[] prevKey

private RowLocationRetRowSource rowSource

Fields
Modifier and Type	Field and Description
`private long[]`	`cardinality`
`private long`	`numRows`
`private DataValueDescriptor[]`	`prevKey`
`private RowLocationRetRowSource`	`rowSource`

Constructor Summary

Constructors
Constructor and Description

CardinalityCounter(RowLocationRetRowSource rowSource)

Constructors
Constructor and Description
`CardinalityCounter(RowLocationRetRowSource rowSource)`

Method Summary

Methods
Modifier and Type	Method and Description
`private DataValueDescriptor[]`	`clone(DataValueDescriptor[] clonee)`
`void`	`closeRowSource()` closeRowSource tells the RowSource that it will no longer need to return any rows and it can release any resource it may have.
`long[]`	`getCardinality()` return the array of cardinalities that are kept internally.
`DataValueDescriptor[]`	`getNextRowFromRowSource()` Gets next row from the row source and update the count of unique values that are returned.
`long`	`getRowCount()` get the number of rows seen in the row source thus far.
`FormatableBitSet`	`getValidColumns()` getValidColumns describes the DataValueDescriptor[] returned by all calls to the getNextRowFromRowSource() call.
`void`	`keepCount(DataValueDescriptor[] currentKey)`
`boolean`	`needsRowLocation()` needsRowLocation returns true iff this the row source expects the drainer of the row source to call rowLocation after getting a row from getNextRowFromRowSource.
`boolean`	`needsToClone()` Does the caller of getNextRowFromRowSource() need to clone the row in order to keep a reference to the row past the getNextRowFromRowSource() call which returned the row.
`void`	`rowLocation(RowLocation rl)` rowLocation is a callback for the drainer of the row source to return the rowLocation of the current row, i.e, the row that is being returned by getNextRowFromRowSource.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - rowSource
```
private RowLocationRetRowSource rowSource
```
  - prevKey
```
private DataValueDescriptor[] prevKey
```
  - cardinality
```
private long[] cardinality
```
  - numRows
```
private long numRows
```
- Constructor Detail
  - CardinalityCounter
```
public CardinalityCounter(RowLocationRetRowSource rowSource)
```
- Method Detail
  - needsRowLocation
```
public boolean needsRowLocation()
```
    Description copied from interface: RowLocationRetRowSource
    
    needsRowLocation returns true iff this the row source expects the drainer of the row source to call rowLocation after getting a row from getNextRowFromRowSource.
    
    Specified by:
    
    needsRowLocation in interface RowLocationRetRowSource
    
    Returns:
    true iff this row source expects some row location to be returned
    See Also:
    RowLocationRetRowSource.needsRowLocation()
  - rowLocation
```
public void rowLocation(RowLocation rl)
                 throws StandardException
```
    Description copied from interface: RowLocationRetRowSource
    rowLocation is a callback for the drainer of the row source to return the rowLocation of the current row, i.e, the row that is being returned by getNextRowFromRowSource. This interface is for the purpose of loading a base table with index. In that case, the indices can be built at the same time the base table is laid down once the row location of the base row is known. This is an example pseudo code on how this call is expected to be used:
```
                boolean needsRL = rowSource.needsRowLocation();
                DataValueDescriptor[] row;
                while((row = rowSource.getNextRowFromRowSource()) != null)
                {
                        RowLocation rl = heapConglomerate.insertRow(row);
                        if (needsRL)
                                rowSource.rowLocation(rl);
                }
                
```
    NeedsRowLocation and rowLocation will ONLY be called by a drainer of the row source which CAN return a row location. Drainer of row source which cannot return rowLocation will guarentee to not call either callbacks. Conversely, if NeedsRowLocation is called and it returns true, then for every row return by getNextRowFromRowSource, a rowLocation callback must also be issued with the row location of the row. Implementor of both the source and the drain of the row source must be aware of this protocol.
    The RowLocation object is own by the caller of rowLocation, in other words, the drainer of the RowSource. This is so that we don't need to new a row location for every row. If the Row Source wants to keep the row location, it needs to clone it (RowLocation is a ClonableObject).
    Specified by:
    
    rowLocation in interface RowLocationRetRowSource
    
    Throws:
    
    StandardException - on error
    See Also:
    RowLocationRetRowSource.rowLocation(org.apache.derby.iapi.types.RowLocation)
  - getNextRowFromRowSource
```
public DataValueDescriptor[] getNextRowFromRowSource()
                                              throws StandardException
```
    Gets next row from the row source and update the count of unique values that are returned.
    
    Specified by:
    
    getNextRowFromRowSource in interface RowSource
    
    Throws:
    
    StandardException - Standard Derby Error Policy
    See Also:
    RowSource.getNextRowFromRowSource()
  - needsToClone
```
public boolean needsToClone()
```
    Description copied from interface: RowSource
    
    Does the caller of getNextRowFromRowSource() need to clone the row in order to keep a reference to the row past the getNextRowFromRowSource() call which returned the row. This call must always return the same for all rows in a RowSource (ie. the caller will call this once per scan from a RowSource and assume the behavior is true for all rows in the RowSource).
    
    Specified by:
    
    needsToClone in interface RowSource
    
    See Also:
    RowSource.needsToClone()
  - getValidColumns
```
public FormatableBitSet getValidColumns()
```
    Description copied from interface: RowSource
    
    getValidColumns describes the DataValueDescriptor[] returned by all calls to the getNextRowFromRowSource() call. If getValidColumns returns null, the number of columns is given by the DataValueDescriptor.length where DataValueDescriptor[] is returned by the preceeding getNextRowFromRowSource() call. Column N maps to DataValueDescriptor[N], where column numbers start at zero. If getValidColumns return a non null validColumns FormatableBitSet the number of columns is given by the number of bits set in validColumns. Column N is not in the partial row if validColumns.get(N) returns false. Column N is in the partial row if validColumns.get(N) returns true. If column N is in the partial row then it maps to DataValueDescriptor[M] where M is the count of calls to validColumns.get(i) that return true where i < N. If DataValueDescriptor.length is greater than the number of columns indicated by validColumns the extra entries are ignored.
    
    Specified by:
    
    getValidColumns in interface RowSource
    
    See Also:
    RowSource.getValidColumns()
  - closeRowSource
```
public void closeRowSource()
```
    Description copied from interface: RowSource
    
    closeRowSource tells the RowSource that it will no longer need to return any rows and it can release any resource it may have. Subsequent call to any method on the RowSource will result in undefined behavior. A closed rowSource can be closed again.
    
    Specified by:
    
    closeRowSource in interface RowSource
    
    See Also:
    RowSource.closeRowSource()
  - clone
```
private DataValueDescriptor[] clone(DataValueDescriptor[] clonee)
```
  - keepCount
```
public void keepCount(DataValueDescriptor[] currentKey)
               throws StandardException
```
    Throws:
    
    StandardException
  - getCardinality
```
public long[] getCardinality()
```
    return the array of cardinalities that are kept internally. One value for each leading key; i.e c1, (c1,c2), (c1,c2,c3) etc.
    
    Returns:
    an array of unique values.
  - getRowCount
```
public long getRowCount()
```
    get the number of rows seen in the row source thus far.
    
    Returns:
    total rows seen from the row source.

Class CardinalityCounter

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

rowSource

prevKey

cardinality

numRows

Constructor Detail

CardinalityCounter

Method Detail

needsRowLocation

rowLocation

getNextRowFromRowSource

needsToClone

getValidColumns

closeRowSource

clone

keepCount

getCardinality

getRowCount