Consistent hashing for Python
Project description
Copyright (c) 2010 by Joachim Bauch, mail@joachim-bauch.de http://www.joachim-bauch.de/projects/python-continuum/
python-continuum provides a function to do consistent hashing. See wikipedia [1] for more informations about this technique.
First we need the continuum object that serves as storage for server informations and can later be used to resolve keys:
>>> from continuum import Continuum >>> c = Continuum()
Empty continuums obviously can’t be queried:
>>> c.resolve('my-key1') Traceback (most recent call last): ... IndexError: empty continuum
Add the server objects that are available as backends:
>>> c.add_server('192.168.0.1', 8080) <Server "192.168.0.1:8080", capacity=1> >>> c.add_server('192.168.0.2', 8080) <Server "192.168.0.2:8080", capacity=1>
You can also specify different capacities of the server to priorize them (this defaults to 1):
>>> c.add_server('192.168.0.3', 8080, 2) <Server "192.168.0.3:8080", capacity=2>
Server objects can also be removed:
>>> server = c.add_server('192.168.0.4', 8080) >>> c.remove_server(server) >>> len(c) 3
Please note that a server can only be added once:
>>> c.add_server('192.168.0.2', 8080) Traceback (most recent call last): ... TypeError: server already added
After all servers have been added, the continuum can be queried for the server that should be used for a given (string) key:
>>> c.resolve('my-first-key') <Server "192.168.0.1:8080", capacity=1> >>> c.resolve('my-other-key') <Server "192.168.0.3:8080", capacity=2>
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