org.apache.derby.iapi.store.access

Class DiskHashtable

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

Constructor Summary

Constructors

Constructor and 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

Modifier and Type	Method and 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.
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.
int	size()

Methods inherited from class java.lang.Object

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

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

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.