最近开始Swift源码分析，无非就是不想纸上谈兵，究竟是用什么算法，和方法实现的功能，所以决定开始写源码分析。 当你安装完swift,你需要做的第一件事情就是创建ring文件，而你用的第一个命令就
最近开始Swift源码分析，无非就是不想纸上谈兵，究竟是用什么算法，和方法实现的功能，所以决定开始写源码分析。
当你安装完swift,你需要做的第一件事情就是创建ring文件，而你用的第一个命令就是swift-ring-builder。swift-ring-builder文件位于源码的bin目录下，是swift最基本的命令，它与swift/common/ring/下的文件一起实现ring文件创建，添加，平衡，等操作。
对于初学者（比如说我）重写源码片段，可以更加深入的了解源码的原理，同时还能对python语言以及相关的库有更深的了解，swift-ring-builder中主要的功能实现就是在Commands类中，比如default(),create(),add(),rebalance()等， 然后main方法会根据你提供的相应参数，来提供执行相应的方法，然后其中的方法会调用/swift/common/ring/下的builder.py中相应的方法最终实现相应的操作，
当我们通过create创建account.builder文件的时候，commod == argv[2] 也就是create 然后执行create来创建account.builder。之后的操作，只要是存在account.builder文件，就会打开这个文件，生产builder实例，来进行相应的操作。其中的 default方法是显示当前的builder信息，可以用来在rebalance之前 检查add的device 。
其中reblance是最重要的方法，当中会涉及到/swift/common/ring下的ring.py builder.py utils.py文件，涉及到了一致性哈希算法和策略的实现，下个博客会具体分析。
代码片段：基本就是把源码抽出来，没写什么注释和异常处理，生成的builder文件，可以通过diff命令，比较是否跟使用swift-ring-builder命令创建的builder文件一样（答案当然是肯定的）。
#! /usr/bin/env pythonfrom sys import argv, exit, modulesimport cPickle as picklefrom os.path import basename, dirname, exists, join as pathjoinfrom itertools import islice, izipfrom builder import RingBuilderMAJOR_VERSION = 1MINOR_VERSION = 3EXIT_SUCCESS = 0EXIT_WARNING = 1EXIT_ERROR = 2class Commands: def unknown(): print 'Unknown command: %s' % argv[2] exit(EXIT_ERROR) def create(): """ my-ring-builder <builder_file> create <part_power> <replicas> <min_part_hours> """ if len(argv) < 6: print Commands.create.__doc__.strip() exit(EXIT_ERROR) builder = RingBuilder(int(argv[3]), int(argv[4]), int(argv[5])) pickle.dump(builder.to_dict(), open(argv[1], 'wb'), protocol=2) exit(EXIT_SUCCESS) def default(): """ Shows information about the ring and the devices within. """ print '%s, build version %d ' % (argv[1], builder.version) zones = 0 balance = 0 if builder.devs: zones = len(set(d['zone'] for d in builder.devs if d is not None)) #blance = builder.get_balance() print '%d partitions, %d replicas, %d zones, %d devices' / % (builder.parts, builder.replicas, zones, len([d for d in builder.devs if d])) print 'The minimun number of hours before a partition can be' / 'reassigned is %s' % builder.min_part_hours if builder.devs: print 'Devices: id zone ip address port name' / 'weight partition' weighted_parts = builder.parts * builder.replicas / / sum(d['weight'] for d in builder.devs if d is not None) for dev in builder.devs: if dev is None: continue if not dev['weight']: if dev['parts']: blance = 999.99 else: blance = 0 else: blance = 100.0 * dev['parts'] / / (dev['weight'] * weighted_parts) - 100.0 print ' %5d %5d %15s %5d %9s %6.02f %10s' % / (dev['id'], dev['zone'], dev['ip'], dev['port'], dev['device'], dev['weight'], dev['parts']) exit(EXIT_SUCCESS) def add(): """ ....... """ dev_and_weights = izip(islice(argv, 3, len(argv), 2), islice(argv, 4, len(argv), 2)) for devstr, weightstr in dev_and_weights: if not devstr.startswith('z'): print 'Invalid add value: %s' % devstr exit(EXIT_ERROR) i = 1 while i < len(devstr) and devstr[i].isdigit(): i += 1 zone = int(devstr[1:i]) rest = devstr[i:] i = 1 while i < len(rest) and rest[i] in '0123456789.': i += 1 ip = rest[1:i] rest = rest[i:] print ip i = 1 while i < len(rest) and rest[i].isdigit(): i += 1 port = int(rest[1:i]) rest = rest[i:] i = 1 while i < len(rest) and rest[i] != '_': i += 1 device_name = rest[1:i] rest = rest[i:] meta = '' if rest.startswith('_'): meta = rest[1:] weight = float(weightstr) for dev in builder.devs: if dev is None: continue if dev['ip'] == ip and dev['port'] == port and / dev['device'] == device_name: print 'already uses %s' exit(EXIT_ERROR) next_dev_id = 0 if builder.devs: next_dev_id = max(d['id'] for d in builder.devs if d) + 1 builder.add_dev({'id': next_dev_id, 'zone': zone, 'ip': ip, 'port': port, 'device': device_name, 'weight': weight, 'meta': meta}) print 'Device z%s-[%s]:%s/%s_"%s" with %s weight got id %s' % / (zone, ip, port, device_name, meta, weight, next_dev_id) pickle.dump(builder.to_dict(), open(argv[1], 'wb'), protocol=2) exit(EXIT_SUCCESS) def rebalance(): """ Attempts to rebalance the ring by reassigning partitions """ devs_changed = builder.devs_changed last_balance = builder.get_balance() parts, balance = builder.rebalance() builder.validate() print 'Reassigned %d (%.02f%%) partitions. Balance is now %.02f.' % / (parts, 100.0*parts / builder.parts, balance) status = EXIT_SUCCESS if balance > 5: print'NOTE: Balance of %.02f indicates you should push the' % / balance status = EXIT_WARNING builder.get_ring().save(ring_file) pickle.dump(builder.to_dict(), open(argv[1], 'wb'), protocol=2) exit(status)if __name__ == '__main__': if exists(argv[1]): builder = pickle.load(open(argv[1], 'rb')) if not hasattr(builder, 'devs'): builder_dict = builder builder = RingBuilder(1, 1, 1) builder.copy_from(builder_dict) ring_file = argv[1] if ring_file.endswith('.builder'): ring_file = ring_file[:-len('.builder')] ring_file += '.ring.gz' if len(argv) == 2: command = "default" else: command = argv[2] Commands.__dict__.get(command, Commands.unknown)()
