336 |
a timestamp and a serial number. |
a timestamp and a serial number. |
337 |
The most current heartbeat is obtained by sending a request |
The most current heartbeat is obtained by sending a request |
338 |
to the primary replica [#consistencytime]_. |
to the primary replica [#consistencytime]_. |
339 |
OceanStore is unique among the versioned P2P systems |
OceanStore |
340 |
in that it implements non-destructive updates, |
implements non-destructive updates, |
341 |
allowing previous versions of documents to be accessed |
allowing previous versions of documents to be accessed |
342 |
(by finding their old heartbeats through Tapestry). |
(by finding their old heartbeats through Tapestry). |
343 |
However, heartbeats are network-internal objects |
However, heartbeats are network-internal objects |
345 |
presented to the user. Therefore, even in OceanStore, |
presented to the user. Therefore, even in OceanStore, |
346 |
a user cannot simply download a version of a file |
a user cannot simply download a version of a file |
347 |
and an associated heartbeat and store them on their |
and an associated heartbeat and store them on their |
348 |
harddisk to keep the version "alive." |
harddisk to keep the version "alive." Of course, the |
349 |
|
very idea of Oceanstore is to make this unnecessary |
350 |
|
by reliably archiving *everything*, but whether this |
351 |
|
will succeed remains to be seen. |
352 |
|
|
353 |
.. [#consistencytime] Many applications |
.. [#consistencytime] Many applications |
354 |
are believed to be able to cope with looser consistency |
are believed to be able to cope with looser consistency |
355 |
semantics; for example, the NFS client for OceanStore only requests |
semantics; for example, the NFS client for OceanStore only requests |
356 |
new heartbeats less than 30 seconds old. |
new heartbeats less than 30 seconds old. |
357 |
|
|
358 |
|
.. is unique among the versioned P2P systems |
359 |
|
in that it |
360 |
|
|
361 |
Pointer records |
Pointer records |
362 |
=============== |
=============== |