ostore.archive
Class GenerateFragsStage

java.lang.Object
  |
  +--ostore.archive.GenerateFragsStage

All Implemented Interfaces:

EventHandlerIF, ProfilableIF

public class GenerateFragsStage

extends Object

implements EventHandlerIF, ProfilableIF

The GenerateChkptStage generates a checkpoint for a particular version. The result is a V-GUID or version GUID.

The GenerateChkptStage creates a checkpoint by sending a GenerateFragsBlkReq for each uniquely modified VerifiableBlock. When the checkpointing process is done, all uniquely modified VerifiableBlocks have been Erasure encoded into n Fragments and a BucketsToDisseminateEvent containing the resulting GUID's of all the uniquely modified VerifiableBlocks has been dispatched.

Fragments are the main mechanism that provides durability in OceanStore. Each Fragment is self-verifying and the cornerstone of the archival layer's fault tolerance and automatic repair. A Fragment is produced from an Erasure coding process, where the Erasure code treats input data as a series of m Fragments, which it transforms into n Fragment, where n > m. The resulting code's essential perperty is that any m of the coded Fragments are sufficient to reconstruct the original data. The rate of encoding is r = m/n<1. The storage overhead is 1/r. The system can adjust the durability of information by selecting the rate (and hence storage overhead).

USAGE

To create a checkpoint dispatch a GenerateFragsChkptReq containing the CacheableIdentity (i.e. VHASH) of the top VerifiableBlock, the number of Fragments to Erasure encode, the inverse rate of encoding, and the Erasure code type. The local GenerateChkptStage will receive the checkpoint request message and return a GenerateFragsChkptResp that either includes the resulting V-GUID.

INITIALIZATION PARAMETERS

node_id

NodeId of the local server where this stage is running.

Version:

$Id: GenerateFragsStage.java,v 1.64 2004/05/13 20:13:06 hweather Exp $

Author:

Hakim Weatherspoon

See Also:

GenerateFragsBlkReq, GenerateFragsBlkResp, GenerateFragsChkptReq, GenerateFragsChkptResp, BucketsToDisseminateEvent, Erasure, Disseminatable, Fragment, VerifiableBlock, DataObject, Btree.InteriorNode, DataObject.DataBlock

Constructor Summary

GenerateFragsStage()

Method Summary

void	destroy()
static SinkIF	getInstance(NodeId node_id) getInstance returns the SinkIF associated with the given node_id.
void	handleEvent(QueueElementIF item)
void	handleEvents(QueueElementIF[] items)
void	init(ConfigDataIF config)
int	profileSize()

Methods inherited from class java.lang.Object

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

Constructor Detail

GenerateFragsStage

public GenerateFragsStage()

Method Detail

getInstance

public static SinkIF getInstance(NodeId node_id)

getInstance returns the SinkIF associated with the given node_id.

Parameters:

node_id - = NodeId to test.

Returns:

SinkIF instance assiociated with given node_id.

handleEvent

public void handleEvent(QueueElementIF item)
                 throws EventHandlerException

Specified by:

handleEvent in interface EventHandlerIF

EventHandlerException

handleEvents

public void handleEvents(QueueElementIF[] items)
                  throws EventHandlerException

Specified by:

handleEvents in interface EventHandlerIF

EventHandlerException

init

public void init(ConfigDataIF config)
          throws Exception

Specified by:

init in interface EventHandlerIF

Exception

destroy

public void destroy()
             throws Exception

Specified by:

destroy in interface EventHandlerIF

Exception

profileSize

public int profileSize()

Specified by:

profileSize in interface ProfilableIF