org.datanucleus.store.valuegenerator

Class AUIDGenerator

java.lang.Object

org.datanucleus.store.valuegenerator.AbstractGenerator<String>

org.datanucleus.store.valuegenerator.AUIDGenerator

All Implemented Interfaces:

ValueGenerator<String>

public class AUIDGenerator
extends AbstractGenerator<String>

This generator uses a Java implementation of DCE UUIDs to create unique identifiers without the overhead of additional database transactions or even an open database connection. The identifiers are Strings of the form "LLLLLLLL-MMMM-HHHH-CCCC-NNNNNNNNNNNN" where 'L', 'M', 'H', 'C' and 'N' are the DCE UUID fields named time low, time mid, time high, clock sequence and node.

This generator can be used in concurrent applications. It is especially useful in situations where large numbers of transactions within a certain amount of time have to be made, and the additional overhead of synchronizing the concurrent creation of unique identifiers through the database would break performance limits.

There are no properties for this ValueGenerator.

Note: Due to limitations of the available Java API there is a chance of less than 1:2^62 that two concurrently running JVMs will produce the same identifiers, which is in practical terms never, because your database server will have crashed a million times before this happens.

Field Summary

Fields inherited from class org.datanucleus.store.valuegenerator.AbstractGenerator

allocationSize, block, initialValue, name, properties, repositoryExists

Fields inherited from interface org.datanucleus.store.valuegenerator.ValueGenerator

PROPERTY_CATALOG_NAME, PROPERTY_CLASS_NAME, PROPERTY_COLUMN_NAME, PROPERTY_FIELD_NAME, PROPERTY_KEY_CACHE_SIZE, PROPERTY_KEY_DATABASE_CACHE_SIZE, PROPERTY_KEY_INITIAL_VALUE, PROPERTY_KEY_MAX_VALUE, PROPERTY_KEY_MIN_VALUE, PROPERTY_ROOT_CLASS_NAME, PROPERTY_SCHEMA_NAME, PROPERTY_SEQUENCE_NAME, PROPERTY_SEQUENCETABLE_CATALOG, PROPERTY_SEQUENCETABLE_NAME_COLUMN, PROPERTY_SEQUENCETABLE_NEXTVAL_COLUMN, PROPERTY_SEQUENCETABLE_SCHEMA, PROPERTY_SEQUENCETABLE_TABLE, PROPERTY_TABLE_NAME

Constructor Summary

Constructors

Constructor and Description
AUIDGenerator(String name, Properties props)

Method Summary

Modifier and Type	Method and Description
static Class	getStorageClass() Accessor for the storage class for values generated with this generator.
protected ValueGenerationBlock<String>	reserveBlock(long size) Method to reserve "size" values to the block.

Methods inherited from class org.datanucleus.store.valuegenerator.AbstractGenerator

allocate, createRepository, current, currentValue, getName, next, nextValue, obtainGenerationBlock, obtainGenerationBlock, repositoryExists, requiresRepository, reserveBlock

Methods inherited from class java.lang.Object

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

Constructor Detail

AUIDGenerator

public AUIDGenerator(String name,
                     Properties props)

Method Detail

getStorageClass

public static Class getStorageClass()

Accessor for the storage class for values generated with this generator.

Returns:

Storage class (in this case String.class)

reserveBlock

protected ValueGenerationBlock<String> reserveBlock(long size)

Method to reserve "size" values to the block.

Specified by:

reserveBlock in class AbstractGenerator<String>

Parameters:

size - The block size

Returns:

The reserved block