# MySQL Connector/Python - MySQL driver written in Python.
# Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.
# MySQL Connector/Python is licensed under the terms of the GPLv2
# <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most
# MySQL Connectors. There are special exceptions to the terms and
# conditions of the GPLv2 as it is applied to this software, see the
# FOSS License Exception
# <http://www.mysql.com/about/legal/licensing/foss-exception.html>.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
"""Implementing load balancing"""
import decimal
def _calc_ratio(part, whole):
"""Calculate ratio
Returns int
"""
return int((part/whole*100).quantize(
decimal.Decimal('1'), rounding=decimal.ROUND_HALF_DOWN))
class BaseScheduling(object):
"""Base class for all scheduling classes dealing with load balancing"""
def __init__(self):
"""Initialize"""
self._members = []
self._ratios = []
def set_members(self, *args):
"""Set members and ratios
This methods sets the members using the arguments passed. Each
argument must be a sequence where the second item is the weight.
The first element is an identifier. For example:
('server1', 0.6), ('server2', 0.8)
Setting members means that the load will be reset. If the members
are the same as previously set, nothing will be reset or set.
If no arguments were given the members will be set to an empty
list.
Raises ValueError when weight can't be converted to a Decimal.
"""
raise NotImplementedError
def get_next(self):
"""Returns the next member"""
raise NotImplementedError
@property
def members(self):
"""Returns the members of this loadbalancer"""
return self._members
@property
def ratios(self):
"""Returns the ratios for all members"""
return self._ratios
class WeightedRoundRobin(BaseScheduling):
"""Class for doing Weighted Round Robin balancing"""
def __init__(self, *args):
"""Initializing"""
super(WeightedRoundRobin, self).__init__()
self._load = []
self._next_member = 0
self._nr_members = 0
if args:
self.set_members(*args)
@property
def load(self):
"""Returns the current load"""
return self._load
def set_members(self, *args):
if not args:
# Reset members if nothing was given
self._members = []
return
new_members = []
for member in args:
member = list(member)
try:
member[1] = decimal.Decimal(str(member[1]))
except decimal.InvalidOperation:
raise ValueError("Member '{member}' is invalid".format(
member=member))
new_members.append(tuple(member))
new_members.sort(key=lambda x: x[1], reverse=True)
if self._members == new_members:
return
self._members = new_members
self._nr_members = len(new_members)
min_weight = min(i[1] for i in self._members)
self._ratios = []
for _, weight in self._members:
self._ratios.append(int(weight/min_weight * 100))
self.reset()
def reset(self):
"""Reset the load"""
self._next_member = 0
self._load = [0] * self._nr_members
def get_next(self):
"""Returns the next member"""
if self._ratios == self._load:
self.reset()
# Figure out the member to return
current = self._next_member
while self._load[current] == self._ratios[current]:
current = (current + 1) % self._nr_members
# Update the load and set next member
self._load[current] += 1
self._next_member = (current + 1) % self._nr_members
# Return current
return self._members[current]
def __repr__(self):
return "{class_}(load={load}, ratios={ratios})".format(
class_=self.__class__,
load=self.load,
ratios=self.ratios
)
def __eq__(self, other):
return self._members == other.members
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