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https://github.com/seomoz/simhash-cluster

A cluster implementation of simhash near-duplicate detection
https://github.com/seomoz/simhash-cluster

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A cluster implementation of simhash near-duplicate detection

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README 

        
Simhash Cluster

===============

![Status: Deprecated](https://img.shields.io/badge/status-deprecated-red.svg?style=flat)

![Team: Big Data](https://img.shields.io/badge/team-big_data-green.svg?style=flat)

![Scope: External](https://img.shields.io/badge/scope-external-green.svg?style=flat)

![Open Source: MIT](https://img.shields.io/badge/open_source-MIT-green.svg?style=flat)

![Critical: No](https://img.shields.io/badge/critical-no-red.svg?style=flat)



__This is obviously unfinished work and we also have no intention of finishing

it. Instead, we've elected to use a real database backing a simhash corpus

through [simhash-db-py](https://github.com/seomoz/simhash-db-py).__



Simhash takes an input vector of integers, and produces a single integer output

that's representative of that vector in the sense that _similar_ vectors yield

_similar_ hashes -- their resultant hashes are expected to differ by only a few

bits. With this in mind, simhash is often used in conjunction with a rolling

hash function on text to generate the input vector, and thus yield a hash that

corresponds to that block of text. In this way, you can quickly identify all the

documents that would be considered near-duplicates.



You can even construct tables to perform these queries very quickly indeed. 

Sadly, it can consume a fair amount of RAM, especially when you insert several 

hundred million or several billion hashes into the corpus of known hashes. And

so, a distributed form is necessary. This is that distributed form.



Architecture

============

There's one master node which slave nodes register with, at which point they are

assigned shards to serve and all queries to that shard will be served by that

node. The master and slaves communicate with zerorpc.



Adapters

========

Adapters are the mechanism by which the cluster is accessed; `simhash-cluster`

comes with two by default (one HTTP, and one zerorpc). All queries are directed

at the master node.



Storage

=======

There's an assumption that you'd like to persist your corpus of known hashes as

it might have developed over time. Like adapters, storage backends are pluggable

and simply must support a few methods like `save` and `load.`



Starting

========

The master node requires a yaml configuration file (an example file is included)

that describes the adapters and storage to use, as well as the simhash 

configuration. With the configuration in place:



    simhash-master --config example-config.yaml



This starts the master daemon (and adapters) running, and the master listening

on port 1234. Slaves should then be started (on any node) and pointing to the

master:



    simhash-slave :1234



Querying

========

Once the master node is running, you can begin querying. Assuming the master 

daemon is running on `localhost`:



    # Using the http interface

    import simplejson as json

    # Add a bunch of hashes

    requests.put('http://localhost:8080/hashes', json.dumps(range(10000)))

    # Find the first similar hash

    requests.get('http://localhost:8080/first/12345').content

    # Find all similar hashes

    requests.get('http://localhost:8080/all/12345').content

    # Remove a particular hash

    requests.delete('http://localhost:8080/hashes/12345')



And now using the `zerorpc` interface:



    import zerorpc

    c = zerorpc.Client('tcp://localhost:5678')

    # Insert hashes

    c.insert(*range(10000))

    # And find first and all

    c.find_first(*range(10000))

    c.find_all(*range(10000))

    # And remove all of them if you'd like

    c.remove(*range(10000))