1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
|
# vim: tabstop=4 shiftwidth=4 softtabstop=4
# Copyright 2013 Hewlett-Packard Development Company, L.P.
# All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
import array
import hashlib
import struct
from oslo.config import cfg
hash_opts = [
cfg.IntOpt('hash_partition_exponent',
default=16,
help='Exponent to determine number of hash partitions to use '
'when distributing load across conductors. Larger values '
'will result in more even distribution of load and less '
'load when rebalancing the ring, but more memory usage. '
'Number of partitions is (2^hash_partition_exponent).'),
cfg.IntOpt('hash_distribution_replicas',
default=2,
help='Number of hosts to map onto each hash partition. '
'Setting this to more than one will cause additional '
'conductor services to prepare deployment environments '
'and potentially allow the Ironic cluster to recover '
'more quickly if a conductor instance is terminated.'),
]
CONF = cfg.CONF
CONF.register_opts(hash_opts)
class HashRing(object):
def __init__(self, hosts, replicas=CONF.hash_distribution_replicas):
"""Create a new hash ring across the specified hosts.
:param hosts: an iterable of hosts which will be mapped.
:param replicas: number of hosts to map to each hash partition,
or len(hosts), which ever is lesser.
Default: CONF.hash_distribution_replicas
"""
self.hosts = list(hosts)
self.replicas = replicas if replicas <= len(hosts) else len(hosts)
self.partition_shift = 32 - CONF.hash_partition_exponent
self.part2host = array.array('H')
for p in range(2 ** CONF.hash_partition_exponent):
self.part2host.append(p % len(hosts))
def _get_partition(self, data):
return (struct.unpack_from('>I', hashlib.md5(data).digest())[0]
>> self.partition_shift)
def get_hosts(self, data, ignore_hosts=None):
"""Get the list of hosts which the supplied data maps onto.
:param data: A string identifier to be mapped across the ring.
:param ignore_hosts: A list of hosts to skip when performing the hash.
Useful to temporarily skip down hosts without
performing a full rebalance.
Default: None.
:returns: a list of hosts.
The length of this list depends on the number of replicas
this `HashRing` was created with. It may be less than this
if ignore_hosts is not None.
"""
host_ids = []
if ignore_hosts is None:
ignore_host_ids = []
else:
ignore_host_ids = [self.hosts.index(h)
for h in ignore_hosts if h in self.hosts]
partition = self._get_partition(data)
for replica in range(0, self.replicas):
if len(host_ids + ignore_host_ids) == len(self.hosts):
# prevent infinite loop
break
while self.part2host[partition] in host_ids + ignore_host_ids:
partition += 1
if partition >= len(self.part2host):
partition = 0
host_ids.append(self.part2host[partition])
return [self.hosts[h] for h in host_ids]
|
