EP0926608A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Distributed persistent storage for intermittently connected clients
Assignee: Nortel Networks Ltd
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Filing: 1998-11-16
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Granted: —
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Expires: 2018-11-16
Abstract
Abstract A method of maintaining mutual consistency between copies of data stored at nodes in a network, the nodes comprising a server node, and a number of client nodes at remote locations, such as laptop computers linked by cellular telephone connections, the nodes being connected intermittently. Following a reconnection between the remote client node and another of the nodes, timestamp information on objects cached at the other node, is sent to the remote client node. At the remote client node, the timestamp information is compared with corresponding information relating to the local copy, to determine if each of the cached objects is more up to date than the local copy. The cached objects are updated based on the local copy, according to the result of the comparison. This peer to peer resynchronisation means that the server need not monitor and control the process, so the system is more easily scaled up to handle more clients.
Inventors
- 👤 Ken Yat-Wan Chan
- 👤 Eric W. Parsons
- 👤 A. Julian Craddock
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 10:51
CPC Classifications
G; G06; G06F; G06F16/00; G06F16/20; G06F16/27
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
171 words
A method of maintaining mutual consistency between copies of
data stored at nodes in a network, the nodes comprising a server node,
and a number of client nodes at remote locations, the nodes being
connected intermittently, the client nodes comprising applications which
make use of the data, the method comprising the steps of, at a remote one
of the client nodes: following a reconnection between the remote client node and
another of the nodes, receiving from that other node, information relating
to a portion of the data of which there is a local copy at the other client,
and a remote copy at the remote client node, the information showing
how up to date is the local copy; comparing at the remote client node, the information relating to the
remote copy with corresponding information relating to the local copy, to
determine if the remote copy is more up to date than the local copy; and updating the remote copy based on the local copy, according to the
result of the comparison.
Claim 2
Dependent Claim
64 words
A method as claimed in claim 1, further comprising the step of
determining if the content of the remote copy is the same as the content of
the local copy, and initiating at the remote node, a conflict resolution
process in the event that the comparison does not reveal a difference
between the local copy and the remote copy, but the respective contents
differ.
Claim 3
Dependent Claim
55 words
A method as claimed in claim 1 or claim 2, further comprising the
preliminary steps of, during a disconnection, recording which portions of
the local copy have been modified at the other node, wherein the
information received by the remote client node relates to the portion
recorded by the other node as having been modified.
Claim 4
Dependent Claim
38 words
A method as claimed in claim 3, wherein the comparison step is
carried out for each of the recorded portions, modified during the
disconnection, before carrying out the comparison step for a portion
modified subsequent to the reconnection.
Claim 5
Independent Claim
26 words
A method as claimed in any preceding claim, further comprising
the step of locking the remote copy to prevent access to it during the
comparison step.
Claim 6
Independent Claim
40 words
A method as claimed in any preceding claim, further comprising
the preliminary step of determining whether to use the remote copy,
according to whether the information relating to the remote copy has been
received at the first of the clients.
Claim 7
Independent Claim
37 words
A method as claimed in any preceding claim, wherein the copies of
data stored at the nodes comprise a copy of less than all the elements of a
database, and wherein the data comprises object oriented data.
Claim 8
Independent Claim
52 words
A method as claimed in any preceding claim, further comprising
the step of propagating the more up to date copy from the remote client
node to a second other node, which also has a copy of the portion of the
data, when there is a connection made with the second other node.
Claim 9
Independent Claim
16 words
A method as claimed in any preceding claim, wherein the other
node comprises the server node.
Claim 10
Independent Claim
62 words
A method as claimed in any preceding claim, further comprising
the steps of storing in the remote client node, a record of transactions
involving the remote copy before the comparison step; and remedying at least some of the transactions in the event that the
local copy is determined by the comparison step to be more up to date
than the remote copy.
Claim 11
Independent Claim
196 words
A method of carrying out an operation on data stored in a network
of nodes, one of the nodes comprising a server, and others of the nodes
being client nodes, the nodes being connected intermittently, at least some
of the data being cached at a remote one of the client nodes, the method
comprising the steps of: initiating the operation at the remote client; causing a resynchronisation of the cached data, the
resynchronisation comprising the steps of: a) causing a reconnection to another of the nodes; b) receiving from that other node, information relating to a portion
of the cached data of which there is a local copy at the other
client, and a remote copy at the remote client node, the
information showing how up to date is the local copy; c) comparing at the remote client node, the information relating to
the remote copy with corresponding information relating to the
local copy, to determine if the remote copy is more up to date
than the local copy; and d) updating the remote copy based on the local copy, according to
the result of the comparison; and completing the operation on the resynchronised cached data.
Claim 12
Dependent Claim
172 words
A client node for use in a network of nodes, copies of data being
stored at the nodes, one of the nodes comprising a server, and others of
the nodes being for other clients at remote locations, the nodes being
connected intermittently, the client node comprising an application which
makes use of the data, the client node comprising: a connection handler for, following a reconnection between the
client node and another of the nodes, receiving from the other node,
information relating to a portion of the data of which there is a remote
copy at the client node, and a local copy at the other node, the information
showing how up to date is the local copy; a comparator for comparing the information relating to the remote
copy with corresponding information relating to the local copy, to
determine if the local copy is more up to date than the remote copy; and a data handler for updating the remote copy, based on the local
copy, according to the result of the comparison.
Claim 13
Dependent Claim
21 words
A client node as claimed in claim 12, further comprising a monitor
for monitoring the state of connections to neighbouring nodes.
Claim 14
Dependent Claim
34 words
A client node as claimed in claim 11 or claim 12, further comprising
a registry for storing an indication of which portions of the data are being
stored by nodes neighbouring the client node.
Claim 15
Dependent Claim
31 words
A client node as claimed in any one of claims 11 to 13, further
comprising a processor for generating and storing an indication of
whether the local copy has been changed.
References Cited (Backward Citations)
No citation records indexed.
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