39 lines
1.4 KiB
Plaintext
39 lines
1.4 KiB
Plaintext
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= DHT =
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A DHT or Distributed Hash Table is a distributed system that provides a look up
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service, similar to that of a [[hash_table]]. The difference however, is the
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distributed, self organizing nature of such a datastructure. The keys are
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distributed in such a manner that any disruption of nodes causes minimal
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disruption to the availability of the data.
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DHTs are used in cooperative web caching, distributed file systems, domain name
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services, instant messaging, and peer-to-peer file sharing. DHTs are used by
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BitTorrent, Freenet, and [[IPFS]].
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== Structure ==
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A DHT is made up of several components
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* Abstract keyspace
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* IE all 160bit strings
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* Partitioned across all participating nodes
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* Overlay network
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* TCP/IP protocol to allow nodes to find each other
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* Allows node to query network for any vlaue
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=== Insertion ===
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Some _filename_ and _data_ exist. A SHA-1 hash is taken of _filename_ and
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produces a key, _k_, in the specified keyspace. The message `put(k,data)` is
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sent to any node in the network, and is forwarded till the node responsible for
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key _k_ is found, and then that node stores the _data_ and _key_.
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=== Retrieval ===
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A node wants to find some _filename_. They take the SHA-1 hash of _filename_
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and produce some key, _k_. `get(k)` is sent to any other node, and the message
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is propogated through the network till the node responsible for _k_ is found,
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and replies with _data_.
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=== Keyspace Partitioning ===
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