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from hashlib import md5
import bisect
import sys
try:
import mmh3
except ImportError:
mmh3 = None
try:
import pyhash
hasher = pyhash.fnv1a_32()
def fnv32a(data, seed=0x811c9dc5):
return hasher(data, seed=seed)
except ImportError:
def fnv32a(data, seed=0x811c9dc5):
"""
FNV-1a Hash (http://isthe.com/chongo/tech/comp/fnv/) in Python.
Taken from https://gist.github.com/vaiorabbit/5670985
"""
hval = seed
fnv_32_prime = 0x01000193
uint32_max = 2 ** 32
if sys.version_info >= (3, 0):
# data is a bytes object, s is an integer
for s in data:
hval = hval ^ s
hval = (hval * fnv_32_prime) % uint32_max
else:
# data is an str object, s is a single character
for s in data:
hval = hval ^ ord(s)
hval = (hval * fnv_32_prime) % uint32_max
return hval
def compactHash(string):
return md5(string.encode('utf-8')).hexdigest()
def carbonHash(key, hash_type):
if hash_type == 'fnv1a_ch':
big_hash = int(fnv32a(key.encode('utf-8')))
small_hash = (big_hash >> 16) ^ (big_hash & 0xffff)
elif hash_type == 'mmh3_ch':
if mmh3 is None:
raise Exception('Install "mmh3" to use this hashing function.')
small_hash = mmh3.hash(key)
else:
big_hash = compactHash(key)
small_hash = int(big_hash[:4], 16)
return small_hash
class ConsistentHashRing:
def __init__(self, nodes, replica_count=100, hash_type='carbon_ch'):
self.ring = []
self.ring_len = len(self.ring)
self.nodes = set()
self.nodes_len = len(self.nodes)
self.replica_count = replica_count
self.hash_type = hash_type
for node in nodes:
self.add_node(node)
def compute_ring_position(self, key):
return carbonHash(key, self.hash_type)
def add_node(self, key):
self.nodes.add(key)
self.nodes_len = len(self.nodes)
for i in range(self.replica_count):
if self.hash_type == 'fnv1a_ch':
replica_key = "%d-%s" % (i, key[1])
else:
replica_key = "%s:%d" % (key, i)
position = self.compute_ring_position(replica_key)
while position in [r[0] for r in self.ring]:
position = position + 1
entry = (position, key)
bisect.insort(self.ring, entry)
self.ring_len = len(self.ring)
def remove_node(self, key):
self.nodes.discard(key)
self.nodes_len = len(self.nodes)
self.ring = [entry for entry in self.ring if entry[1] != key]
self.ring_len = len(self.ring)
def get_node(self, key):
assert self.ring
position = self.compute_ring_position(key)
search_entry = (position, ())
index = bisect.bisect_left(self.ring, search_entry) % self.ring_len
entry = self.ring[index]
return entry[1]
def get_nodes(self, key):
nodes = set()
if not self.ring:
return
if self.nodes_len == 1:
for node in self.nodes:
yield node
position = self.compute_ring_position(key)
search_entry = (position, ())
index = bisect.bisect_left(self.ring, search_entry) % self.ring_len
last_index = (index - 1) % self.ring_len
nodes_len = len(nodes)
while nodes_len < self.nodes_len and index != last_index:
next_entry = self.ring[index]
(position, next_node) = next_entry
if next_node not in nodes:
nodes.add(next_node)
nodes_len += 1
yield next_node
index = (index + 1) % self.ring_len