DiskHashtable (Apache Derby V10.14 Internals)

java.lang.Object
- org.apache.derby.iapi.store.access.DiskHashtable

```
public class DiskHashtable
extends java.lang.Object
```
This class is used by BackingStoreHashtable when the BackingStoreHashtable must spill to disk. It implements the methods of a hash table: put, get, remove, elements, however it is not implemented as a hash table. In order to minimize the amount of unique code it is implemented using a Btree and a heap conglomerate. The Btree indexes the hash code of the row key. The actual key may be too long for our Btree implementation. Created: Fri Jan 28 13:58:03 2005

Version:

1.0

Nested Class Summary

Nested Classes
Modifier and Type Class Description

private class DiskHashtable.ElementEnum

Nested Classes
Modifier and Type	Class	Description
`private class`	`DiskHashtable.ElementEnum`

Field Summary

Fields
Modifier and Type	Field	Description
`private ConglomerateController`	`btreeConglomerate`
`private long`	`btreeConglomerateId`
`private DataValueDescriptor[]`	`btreeRow`
`private boolean`	`keepAfterCommit`
`private boolean`	`keepStatistics`
`private int[]`	`key_column_numbers`
`private boolean`	`remove_duplicates`
`private DataValueDescriptor[]`	`row`
`private ConglomerateController`	`rowConglomerate`
`private long`	`rowConglomerateId`
`private DataValueDescriptor[]`	`scanKey`
`private int`	`size`
`private TransactionController`	`tc`

Constructor Summary

Constructors
Constructor	Description
`DiskHashtable(TransactionController tc, DataValueDescriptor[] template, int[] collation_ids, int[] key_column_numbers, boolean remove_duplicates, boolean keepAfterCommit)`	Creates a new `DiskHashtable` instance.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`close()`
`java.util.Enumeration<java.lang.Object>`	`elements()`	Return an Enumeration that can be used to scan entire table.
`java.lang.Object`	`get(java.lang.Object key)`	Get a row from the overflow structure.
`private static Context`	`getContextOrNull(java.lang.String contextID)`	Privileged lookup of a Context.
`private java.lang.Object`	`getRemove(java.lang.Object key, boolean remove, boolean existenceOnly)`
`boolean`	`put(java.lang.Object key, java.lang.Object[] row)`	Put a new row in the overflow structure.
`java.lang.Object`	`remove(java.lang.Object key)`	remove all rows with a given key from the hash table.
`private boolean`	`rowMatches(DataValueDescriptor[] row, java.lang.Object key)`
`int`	`size()`

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

- Field Detail
  - rowConglomerateId
```
private final long rowConglomerateId
```
  - rowConglomerate
```
private ConglomerateController rowConglomerate
```
  - btreeConglomerateId
```
private final long btreeConglomerateId
```
  - btreeConglomerate
```
private ConglomerateController btreeConglomerate
```
  - btreeRow
```
private final DataValueDescriptor[] btreeRow
```
  - key_column_numbers
```
private final int[] key_column_numbers
```
  - remove_duplicates
```
private final boolean remove_duplicates
```
  - tc
```
private final TransactionController tc
```
  - row
```
private final DataValueDescriptor[] row
```
  - scanKey
```
private final DataValueDescriptor[] scanKey
```
  - size
```
private int size
```
  - keepStatistics
```
private boolean keepStatistics
```
  - keepAfterCommit
```
private final boolean keepAfterCommit
```
- Constructor Detail
  - DiskHashtable
```
public DiskHashtable(TransactionController tc,
                     DataValueDescriptor[] template,
                     int[] collation_ids,
                     int[] key_column_numbers,
                     boolean remove_duplicates,
                     boolean keepAfterCommit)
              throws StandardException
```
    Creates a new DiskHashtable instance.
    
    Parameters:
    
    tc -
    
    template - An array of DataValueDescriptors that serves as a template for the rows.
    
    key_column_numbers - The indexes of the key columns (0 based)
    
    remove_duplicates - If true then rows with duplicate keys are removed.
    
    keepAfterCommit - If true then the hash table is kept after a commit
    
    Throws:
    
    StandardException
- Method Detail
  - close
```
public void close()
           throws StandardException
```
    Throws:
    
    StandardException
  - put
```
public boolean put(java.lang.Object key,
                   java.lang.Object[] row)
            throws StandardException
```
    Put a new row in the overflow structure.
    
    Parameters:
    
    row - The row to be inserted.
    
    Returns:
    
    true if the row was added, false if it was not added (because it was a duplicate and we are eliminating duplicates).
    
    Throws:
    
    StandardException - standard error policy
  - get
```
public java.lang.Object get(java.lang.Object key)
                     throws StandardException
```
    Get a row from the overflow structure.
    
    Parameters:
    
    key - If the rows only have one key column then the key value. If there is more than one key column then a KeyHasher
    
    Returns:
    
    null if there is no corresponding row, the row (DataValueDescriptor[]) if there is exactly one row with the key, or a Vector of all the rows with the key if there is more than one.
    
    Throws:
    
    StandardException
  - getRemove
```
private java.lang.Object getRemove(java.lang.Object key,
                                   boolean remove,
                                   boolean existenceOnly)
                            throws StandardException
```
    Throws:
    
    StandardException
  - rowMatches
```
private boolean rowMatches(DataValueDescriptor[] row,
                           java.lang.Object key)
```
  - remove
```
public java.lang.Object remove(java.lang.Object key)
                        throws StandardException
```
    remove all rows with a given key from the hash table.
    
    Parameters:
    
    key - The key of the rows to remove.
    
    Returns:
    
    The removed row(s).
    
    Throws:
    
    StandardException - Standard exception policy.
  - size
```
public int size()
```
    Returns:
    
    The number of rows in the hash table
  - elements
```
public java.util.Enumeration<java.lang.Object> elements()
                                                 throws StandardException
```
    Return an Enumeration that can be used to scan entire table.
    RESOLVE - is it worth it to support this routine?
    
    Returns:
    
    The Enumeration.
    
    Throws:
    
    StandardException - Standard exception policy.
  - getContextOrNull
```
private static Context getContextOrNull(java.lang.String contextID)
```
    Privileged lookup of a Context. Must be private so that user code can't call this entry point.

Class DiskHashtable

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

rowConglomerateId

rowConglomerate

btreeConglomerateId

btreeConglomerate

btreeRow

key_column_numbers

remove_duplicates

tc

row

scanKey

size

keepStatistics

keepAfterCommit

Constructor Detail

DiskHashtable

Method Detail

close

put

get

getRemove

rowMatches

remove

size

elements

getContextOrNull