/[gzz]/manuscripts/pointers/article.rst
ViewVC logotype

Diff of /manuscripts/pointers/article.rst

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 1.64 by benja, Sun Nov 2 01:51:41 2003 UTC revision 1.65 by benja, Sun Nov 2 02:21:16 2003 UTC
# Line 103  in the DHT will update a mapping if the Line 103  in the DHT will update a mapping if the
103  is signed with the appropriate key, and contains a timestamp  is signed with the appropriate key, and contains a timestamp
104  newer than that of the current version.  newer than that of the current version.
105    
106  *Oceanstore* [XXXref] XXX  In *Oceanstore* [XXXref], every document has a
107    *primary replica*, a small set of servers that
108    maintain the current version of the document.
109    To make the connection between document and version,
110    the primary replia signs *heartbeats*, tuples
111    containing a document id, the hash of a version,
112    a timestamp and a serial version number.
113    To obtain the most current version, one sends a request
114    to the primary replica. Many applications, however,
115    are believed to be able to cope with loser consistency
116    semantics; the NFS client for CFS only requests
117    new heartbeats less than 30 seconds old.
118    Oceanstore is unique among the versioned P2P systems
119    in that it implements non-destructive updates,
120    allowing previous versions of documents to be accessed
121    (by using their old heartbeats).
122    
123  *Freenet* [XXXref] was originally planned to have an  *Freenet* [XXXref] was originally planned to have an
124  update mechanism where the network would remember  update mechanism where the network would remember
# Line 127  on it to get to a newer version of the d Line 142  on it to get to a newer version of the d
142    
143  Finally, a simplistic approach to P2P versioning  Finally, a simplistic approach to P2P versioning
144  is to have a centralized server keep track of the current version  is to have a centralized server keep track of the current version
145  of a document, such as in the Content-Addressable Web  of a document, such as in the *Content-Addressable Web*
146  proposal [XXXref -> google it], in which clients download  proposal [XXXref -> google it], in which clients download
147  a file's hash through HTTP (using an HTTP URI),  a file's hash through HTTP (using an HTTP URI),
148  then download the file through, e.g., a file-sharing network.  then download the file through, e.g., a file-sharing network.
149  This provides some of the efficiency advantages of a P2P Web.  This provides some of the efficiency advantages of a P2P Web.
150  However, there is still a single point of failure;  However, there is still a single point of failure, and
151  links still break when pages move to a different directory  links still break when pages move to a different directory
152  or Web server; and when the original publisher loses interest  or Web server.
153    
154    In a file-sharing system, a file remains accessible
155    as long as there is a copy on any of the participating hosts.
156    None of the above versioning systems have this property.
157    In CFS, version information is stored in the DHT, and only
158    as long as the publisher regularly requests it to be kept.
159    In OceanStore, requesting a document's current version
160    depends on querying its primary replica; when the primary
161    replica ceases to function, the current version cannot be
162    determined any longer (for some applications, this only happens
163    30 seconds after the primary replica disappears).
164    <<XXX what to say about freenet?>>
165    In the Content-Addressable Web proposal, the situation
166    is the same as on the current Web.
167    
168    Thus, in these systems, when the original publisher loses interest
169  and stops publishing a page, it disappears, even if  and stops publishing a page, it disappears, even if
170  someone else would have kept a copy.  someone else would have kept a copy.
171    
# Line 145  someone else would have kept a copy. Line 176  someone else would have kept a copy.
176    
177  .. Standing on the shoulders of giants: Example of Web links rotting away  .. Standing on the shoulders of giants: Example of Web links rotting away
178    
179  These are important concerns.  This is an important concern.
180  In 1997, NASA launched the Cassini-Huygens spacecraft  In 1997, NASA launched the Cassini-Huygens spacecraft
181  on a mission to Saturn. Before the launch, the mission  on a mission to Saturn. Before the launch, the mission
182  was widely criticized for its use of radioisotope  was widely criticized for its use of radioisotope

Legend:
Removed from v.1.64  
changed lines
  Added in v.1.65

savannah-hackers-public@gnu.org
ViewVC Help
Powered by ViewVC 1.1.26