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information about past versions is not stored at all. |
information about past versions is not stored at all. |
136 |
|
|
137 |
In *OceanStore* [kubiatowicz00oceanstore]_, |
In *OceanStore* [kubiatowicz00oceanstore]_, |
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an Internet-scale distributed data store that |
an Internet-scale distributed data store based |
139 |
|
on Tapestry [zhao01tapestry]_ that |
140 |
allows users to access their files |
allows users to access their files |
141 |
from different locations, every document has a |
from different locations, every document has a |
142 |
*primary replica*, a small set of servers that |
*primary replica*, a small set of servers that |
150 |
OceanStore is unique among the versioned P2P systems |
OceanStore is unique among the versioned P2P systems |
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in that it implements non-destructive updates, |
in that it implements non-destructive updates, |
152 |
allowing previous versions of documents to be accessed |
allowing previous versions of documents to be accessed |
153 |
(by using their old heartbeats). |
(by finding their old heartbeats through Tapestry). |
154 |
In OceanStore, requesting a document's current version |
However, heartbeats are network-internal objects |
155 |
depends on querying its primary replica; when the primary |
that do not exist at the file system interface |
156 |
replica ceases to function, the current version cannot be |
presented to the user. Therefore, even in OceanStore, |
157 |
determined any longer (for some applications, this only happens |
a user cannot simply download a version of a file |
158 |
30 seconds after the primary replica disappears). |
and an associated heartbeat and store them on their |
159 |
|
harddisk to keep the version "alive." |
160 |
|
|
161 |
.. [#consistencytime] Many applications |
.. [#consistencytime] Many applications |
162 |
are believed to be able to cope with looser consistency |
are believed to be able to cope with looser consistency |