129 |
in the DHT will update a mapping if the update message |
in the DHT will update a mapping if the update message |
130 |
is signed with the appropriate key, and contains a timestamp |
is signed with the appropriate key, and contains a timestamp |
131 |
newer than that of the current version. |
newer than that of the current version. |
132 |
|
In CFS, version information is stored in the DHT, and only |
133 |
|
as long as the publisher regularly requests it to be kept; |
134 |
|
information about past versions isn't stored at all. |
135 |
|
|
136 |
In *OceanStore* [kubiatowicz00oceanstore]_, |
In *OceanStore* [kubiatowicz00oceanstore]_, |
137 |
an Internet-scale distributed data store that |
an Internet-scale distributed data store that |
149 |
in that it implements non-destructive updates, |
in that it implements non-destructive updates, |
150 |
allowing previous versions of documents to be accessed |
allowing previous versions of documents to be accessed |
151 |
(by using their old heartbeats). |
(by using their old heartbeats). |
152 |
|
In OceanStore, requesting a document's current version |
153 |
|
depends on querying its primary replica; when the primary |
154 |
|
replica ceases to function, the current version cannot be |
155 |
|
determined any longer (for some applications, this only happens |
156 |
|
30 seconds after the primary replica disappears). |
157 |
|
|
158 |
.. [#consistencytime] Many applications |
.. [#consistencytime] Many applications |
159 |
are believed to be able to cope with looser consistency |
are believed to be able to cope with looser consistency |
178 |
version ``n+1`` is actually inserted into the system; thus, |
version ``n+1`` is actually inserted into the system; thus, |
179 |
when the image does show up, the user knows that they should click |
when the image does show up, the user knows that they should click |
180 |
on it to get to a newer version of the document. |
on it to get to a newer version of the document. |
181 |
|
In Freenet, files only stay online as long as they are |
182 |
|
requested regularly; keeping a copy on your harddisk |
183 |
|
does not keep a page alive. |
184 |
|
|
185 |
Finally, a simplistic approach to P2P versioning |
Finally, a simplistic approach to P2P versioning |
186 |
is to have a centralized server keep track of the current version |
is to have a centralized server keep track of the current version |
192 |
However, there is still a single point of failure, and |
However, there is still a single point of failure, and |
193 |
links still break when pages move to a different directory |
links still break when pages move to a different directory |
194 |
or Web server. |
or Web server. |
|
|
|
|
In a filesharing system, a file remains accessible |
|
|
as long as there is a copy on any of the participating hosts. |
|
|
None of the above versioning systems have this property. |
|
|
In CFS, version information is stored in the DHT, and only |
|
|
as long as the publisher regularly requests it to be kept. |
|
|
In OceanStore, requesting a document's current version |
|
|
depends on querying its primary replica; when the primary |
|
|
replica ceases to function, the current version cannot be |
|
|
determined any longer (for some applications, this only happens |
|
|
30 seconds after the primary replica disappears). |
|
|
In Freenet, files only |
|
|
remain on-line as long as they are requested regularly in any case. |
|
195 |
In the Content-Addressable Web proposal, the situation |
In the Content-Addressable Web proposal, the situation |
196 |
is the same as on the current Web. |
regarding versioning is the same as on the current Web. |
197 |
|
|
198 |
|
In conclusion, a filesharing system, a file remains accessible |
199 |
|
as long as there is a copy on any of the participating hosts; |
200 |
|
none of the above versioning systems have this property. |
201 |
|
|
202 |
Thus, in these systems, when the original publisher loses interest |
Thus, in these systems, when the original publisher loses interest |
203 |
and stops publishing a page, it disappears, even if |
and stops publishing a page, it disappears, even if |