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Networks are more likely to be a Weibull model 15 | # in reality, but this is close enough for the model comparison. 16 | return abs(random.normalvariate(self.mean, self.sd)) 17 | 18 | # Base class for all the backoff implementations 19 | class Backoff: 20 | def __init__(self, base, cap): 21 | self.base = base 22 | self.cap = cap 23 | 24 | def expo(self, n): 25 | return min(self.cap, pow(2, n)*self.base) 26 | 27 | class NoBackoff(Backoff): 28 | def backoff(self, n): 29 | return 0 30 | 31 | class ExpoBackoff(Backoff): 32 | def backoff(self, n): 33 | return self.expo(n) 34 | 35 | class ExpoBackoffEqualJitter(Backoff): 36 | def backoff(self, n): 37 | v = self.expo(n) 38 | return v/2 + random.uniform(0, v/2) 39 | 40 | class ExpoBackoffFullJitter(Backoff): 41 | def backoff(self, n): 42 | v = self.expo(n) 43 | return random.uniform(0, v) 44 | 45 | class ExpoBackoffDecorr(Backoff): 46 | def __init__(self, base, cap): 47 | Backoff.__init__(self, base, cap) 48 | self.sleep = self.base 49 | 50 | def backoff(self, n): 51 | self.sleep = min(self.cap, random.uniform(self.base, self.sleep * 3)) 52 | return self.sleep 53 | 54 | # Small class to track two counters 55 | class Stats: 56 | def __init__(self): 57 | self.failures = 0 58 | self.calls = 0 59 | 60 | # Build a message to be added to the simulated network 61 | def msg(tm, send_to, reply_to, payload): 62 | assert tm >= 0 63 | assert send_to is not None 64 | return (tm, send_to, reply_to, payload) 65 | 66 | # The OCC server. It models a single "row" with a single version. 67 | class OccServer: 68 | def __init__(self, net, stats, ts_f): 69 | self.version = 0 70 | self.net = net 71 | self.stats = stats 72 | self.ts_f = ts_f 73 | 74 | # Try to write the row. If you provide the right version number (obtained from a read), 75 | # the write will succeed. 76 | def write(self, tm, request): 77 | self.ts_f.write("%d\n"%(tm)) 78 | success = False 79 | self.stats.calls += 1 80 | if request[3] == self.version: 81 | self.version += 1 82 | success = True 83 | else: 84 | self.stats.failures += 1 85 | return msg(tm + self.net.delay(), request[2], None, success) 86 | 87 | # Read the current version number of the row. 88 | def read(self, tm, request): 89 | return msg(tm + self.net.delay(), request[2], None, self.version) 90 | 91 | # The OCC client. It models a client that tries to update the row exactly once, 92 | # then stops. 93 | class OccClient: 94 | def __init__(self, server, net, backoff): 95 | self.server = server 96 | self.net = net 97 | self.attempt = 0 98 | self.backoff = backoff 99 | 100 | def start(self, tm): 101 | return msg(tm + self.net.delay(), self.server.read, self.read_rsp, None) 102 | 103 | def read_rsp(self, tm, request): 104 | return msg(tm + self.net.delay(), self.server.write, self.write_rsp, request[3]) 105 | 106 | def write_rsp(self, tm, request): 107 | if not request[3]: 108 | self.attempt += 1 109 | return msg(tm + self.net.delay() + self.backoff.backoff(self.attempt), self.server.read, self.read_rsp, None) 110 | else: 111 | return None 112 | 113 | # The main loop of the simulation. 114 | def run_sim(queue): 115 | tm = 0 116 | while len(queue) > 0: 117 | # Pull an event off the priority queue 118 | msg = heapq.heappop(queue) 119 | assert msg[0] >= tm # TIme must move forward 120 | tm = msg[0] 121 | next_msg = msg[1](tm, msg) 122 | if next_msg is not None: 123 | # If it cause another event to be generated, enqueue it 124 | heapq.heappush(queue, next_msg) 125 | return tm 126 | 127 | # Setup the simulation, creating the clients and server 128 | def setup_sim(clients, backoff_cls, ts_f, stats): 129 | net = Net(10, 2) 130 | queue = [] 131 | server = OccServer(net, stats, ts_f) 132 | for i in xrange(0, clients): 133 | client = OccClient(server, net, backoff_cls(5, 2000)) 134 | heapq.heappush(queue, client.start(0)) 135 | return (queue, stats) 136 | 137 | # The list of backoff types that we simulate over. The tuples are a class 138 | # name and a friendly name for the output. 139 | backoff_types = ((ExpoBackoff, "Exponential"), 140 | (ExpoBackoffDecorr,"Decorr"), 141 | (ExpoBackoffEqualJitter, "EqualJitter"), 142 | (ExpoBackoffFullJitter, "FullJitter"), 143 | (NoBackoff, "None")) 144 | 145 | def run(): 146 | with open("backoff_results.csv", "w") as f: 147 | f.write("clients,time,calls,Algorithm\n") 148 | for i in xrange(1, 20): 149 | clients = i * 10 150 | for backoff in backoff_types: 151 | with open("ts_" + backoff[1], "w") as ts_f: 152 | stats = Stats() 153 | tm = 0 154 | for t in xrange(0, 100): 155 | queue, stats = setup_sim(clients, backoff[0], ts_f, stats) 156 | tm += run_sim(queue) 157 | f.write("%d,%d,%d,%s\n"%(clients, tm/100, stats.calls/100, backoff[1])) 158 | 159 | run() 160 | --------------------------------------------------------------------------------