OpenStack_Swift源代码分析——ObjectReplicator源代码分析(2)

1、Replicator运行代码具体分析

上篇问中介绍了启动Replicator的详细过程，以下解说Replicator的运行代码的详细实现，首先看replicate方法：

def replicate(self, override_devices=None, override_partitions=None):
        """Run a replication pass"""
        self.start = time.time()
        self.suffix_count = 0
        self.suffix_sync = 0
        self.suffix_hash = 0
        self.replication_count = 0
        self.last_replication_count = -1
        self.partition_times = []

        if override_devices is None:
            override_devices = []
        if override_partitions is None:
            override_partitions = []
        #heartbeat 为心跳函数 依据配置，配置没有 默觉得 300
        stats = eventlet.spawn(self.heartbeat)
        #detect_lockup  检查死锁
        lockup_detector = eventlet.spawn(self.detect_lockups)
        eventlet.sleep()  # Give spawns a cycle

        try:
            #replication 的 woker 数量
            self.run_pool = GreenPool(size=self.concurrency)
            # Returns a sorted list of jobs (dictionaries) that specify the
            # partitions, nodes, etc to be synced.
            # 返回专门为分区，节点同步工作的排序的列表
            #
            jobs = self.collect_jobs()
            for job in jobs:
                #重写设备
                if override_devices and job['device'] not in override_devices:
                    continue
                #重写分区
                if override_partitions and \
                        job['partition'] not in override_partitions:
                    continue
                #假设重写设备及其重写分区在job 中
                dev_path = join(self.devices_dir, job['device'])
                if self.mount_check and not ismount(dev_path):
                    self.logger.warn(_('%s is not mounted'), job['device'])
                    continue
                #ring没有改变
                if not self.check_ring():
                    self.logger.info(_("Ring change detected. Aborting "
                                       "current replication pass."))
                    return
                #假设
                if job['delete']:
                    self.run_pool.spawn(self.update_deleted, job)
                else:
                    #运行的是更新
                    self.run_pool.spawn(self.update, job)
            with Timeout(self.lockup_timeout):
                self.run_pool.waitall()
        except (Exception, Timeout):
            self.logger.exception(_("Exception in top-level replication loop"))
            self.kill_coros()
        finally:
            stats.kill()
            lockup_detector.kill()
            self.stats_line()

在replicate方法中，首先是为replicate方法运行的准备工作，当中最重要的是要收集要运行的job的collection_jobs方法，以下为其代码的详细实现：

def collect_jobs(self):
        """
        Returns a sorted list of jobs (dictionaries) that specify the
        partitions, nodes, etc to be synced.
        """
        jobs = []
        ips = whataremyips()
        #replication_ip 和replication_port 在  RingBuilder中 load加入
        #self.object_ring = Ring(self.swift_dir, ring_name='object')
        for local_dev in [dev for dev in self.object_ring.devs
                          if dev and dev['replication_ip'] in ips and
                          dev['replication_port'] == self.port]:
            dev_path = join(self.devices_dir, local_dev['device'])
            obj_path = join(dev_path, 'objects')
            tmp_path = join(dev_path, 'tmp')
            if self.mount_check and not ismount(dev_path):
                self.logger.warn(_('%s is not mounted'), local_dev['device'])
                continue
        #Remove any file in a given path that that was last modified before mtime.
        #/srv/1/node/sdb1/tmp下的文件
            unlink_older_than(tmp_path, time.time() - self.reclaim_age)
            if not os.path.exists(obj_path):
                try:
                    mkdirs(obj_path)
                except Exception:
                    self.logger.exception('ERROR creating %s' % obj_path)
                continue
            #root@kinglion-Lenovo-Product:/srv/1/node/sdb1/objects# ls
            #13069  133971  4799  58208  94238
            for partition in os.listdir(obj_path):
                try:
                    job_path = join(obj_path, partition)
                    #推断当前路径是否为文件，假设是文件则删除
                    if isfile(job_path):
                        #
                        # Clean up any (probably zero-byte) files where a
                        # partition should be.
                        self.logger.warning('Removing partition directory '
                                            'which was a file: %s', job_path)
                        os.remove(job_path)
                        continue
                    #获得每一个partion相应的设备
                    part_nodes = \
                        self.object_ring.get_part_nodes(int(partition))
                    #nodes为不是本机器nodes的其它replica-1个nodes
                    nodes = [node for node in part_nodes
                             if node['id'] != local_dev['id']]
                    #对objects下全部partion遍历，故有jobs的长度最大为_replica2part2dev分区备份中出现此设备有此设备id的分区和
                    jobs.append(
                        dict(path=job_path,
                             device=local_dev['device'],
                             nodes=nodes,
                             #len（nodes）>len(part_nodes)-1的情况是当前节点已经不再是 当前partition所相应的设备了，有可能删除了该设备
                             delete=len(nodes) > len(part_nodes) - 1,
                             partition=partition))
                except (ValueError, OSError):
                    continue
        #打乱顺序
        random.shuffle(jobs)
        if self.handoffs_first:
            # Move the handoff parts to the front of the list
            #将handoff 节点移到jobs队列的前边
            jobs.sort(key=lambda job: not job['delete'])
        self.job_count = len(jobs)
        return jobs

对于第二层for循环，os.listdir(obj_path)列出objects目录下的全部partion，创建object是在objects目录下创建objects所映射的分区号的文件件，再在partion目录下创建以object的hash值后三位为名称的目录，然后再在后缀目录下创建以object的hash值为目录名的目录，object会存储为以object上传时间戳为名.data为文件后缀的文件。通过理解一致性hash算法可知，增加虚拟节点后每个设备会多个虚拟节点和其相应，假设一个设备相应的分区为n则，obj_path下子目录数目会<=n,由于存入的全部文件并不一定都能映射到当前设备所相应的分区。for循环首先判读obj_path下是否为文件，若是文件则删除，若不是则获得该分区号，依据分区号获得该分区号所映射的三个备份设备，并将设备id和本地设备id不想等的增加到nodes中，将nodes、path等信息增加到jobs中，最后打乱jobs的顺序，再将handoff
节点移到队列前边。返回jobs。再到replicate方法，首先我们看job[delete]为False的情况。当job[delete]为False会运行update方法，下边看update方法的详细实现：

def update(self, job):
        """
        High-level method that replicates a single partition.

        :param job: a dict containing info about the partition to be replicated
        """
        self.replication_count += 1
        self.logger.increment('partition.update.count.%s' % (job['device'],))
        begin = time.time()
        try:
            #get_hashes 从hashes.pkl获取hashes值并更新 获取本地的hashes job[path] 为 job_path = join(obj_path, partition) local_hash为hashes.pkl中的反序列化回来的内容 hashed为改变的
            hashed, local_hash = tpool_reraise(
                get_hashes, job['path'],
                do_listdir=(self.replication_count % 10) == 0,
                reclaim_age=self.reclaim_age)
            self.suffix_hash += hashed
            self.logger.update_stats('suffix.hashes', hashed)
            #
            attempts_left = len(job['nodes'])
            #此时的nodes为除去本节点外的全部节点 由于 job['nodes]不包括本地节点get_more_nodes(int(job['partition']))能获得除去本partion所相应节点 外的其它全部节点
            nodes = itertools.chain(
                job['nodes'],
                self.object_ring.get_more_nodes(int(job['partition'])))
           #此时attempts_left 为2 若果replica为3
            while attempts_left > 0:
                # If this throws StopIterator it will be caught way below
                node = next(nodes)
                attempts_left -= 1
                try:
                    with Timeout(self.http_timeout):
                        #REPLICARE方法 相应 sever里面的RELICATE方法
                        resp = http_connect(
                            node['replication_ip'], node['replication_port'],
                            node['device'], job['partition'], 'REPLICATE',
                            '', headers=self.headers).getresponse()
                        if resp.status == HTTP_INSUFFICIENT_STORAGE:
                            self.logger.error(_('%(ip)s/%(device)s responded'
                                                ' as unmounted'), node)
                            attempts_left += 1
                            continue
                        if resp.status != HTTP_OK:
                            self.logger.error(_("Invalid response %(resp)s "
                                                "from %(ip)s"),
                                              {'resp': resp.status,
                                               'ip': node['replication_ip']})
                            continue
                        #remote_hash 为 请求 'REPLICATE 返回的
                        remote_hash = pickle.loads(resp.read())
                        del resp
                    #找出本地后缀和远程后缀不同的
                    suffixes = [suffix for suffix in local_hash if
                                local_hash[suffix] !=
                                remote_hash.get(suffix, -1)]
                    #假设没有说明没有变动，则继续请求下一个节点
                    if not suffixes:
                        continue

                    #效果就是运行get_hashes方法
                    hashed, recalc_hash = tpool_reraise(
                        get_hashes,
                        job['path'], recalculate=suffixes,
                        reclaim_age=self.reclaim_age)
                    self.logger.update_stats('suffix.hashes', hashed)
                    local_hash = recalc_hash
                    #假如 local_hash 为 123 321 122 remote_hash 123 321 124 则 122为变化的
                    #文件路径hash值后三位会不会反复
                    suffixes = [suffix for suffix in local_hash if
                                local_hash[suffix] !=
                                remote_hash.get(suffix, -1)]
                    #找到了不同的并知道其节点则将其同步到相应的节点，是基于推送模式的，故传的数据是自己本地的数据
                    self.sync(node, job, suffixes)  #同步变化的
                    with Timeout(self.http_timeout):
                        conn = http_connect(
                            node['replication_ip'], node['replication_port'],
                            node['device'], job['partition'], 'REPLICATE',
                            '/' + '-'.join(suffixes),
                            headers=self.headers)
                        conn.getresponse().read()
                    self.suffix_sync += len(suffixes)
                    self.logger.update_stats('suffix.syncs', len(suffixes))
                except (Exception, Timeout):
                    self.logger.exception(_("Error syncing with node: %s") %
                                          node)
            #后缀数量 写日志时会用到
            self.suffix_count += len(local_hash)
        except (Exception, Timeout):
            self.logger.exception(_("Error syncing partition"))
        finally:
            self.partition_times.append(time.time() - begin)
            self.logger.timing_since('partition.update.timing', begin)

update方法，中首先是获得本地文件里当前设备所相应hashes.pkl文件里每一个后缀所相应的hahes值，形如{'a83': '0db7b416c9808517a1bb2157af20b09b'},当中key为文件内容hash值的后三字节，value为后缀目录下全部子目录下（即以文件内容的md5值为名字的目录）全部.data文件的文件名称字的md5值,能够理解为全部文件名称的md5值和。

            hashed, local_hash = tpool_reraise(
                get_hashes, job['path'],
                do_listdir=(self.replication_count % 10) == 0,
                reclaim_age=self.reclaim_age)

如上代码片段会运行get_hashes方法，并将后边參数传递给get_hashes

def get_hashes(partition_dir, recalculate=None, do_listdir=False,
               reclaim_age=ONE_WEEK):
    """
    Get a list of hashes for the suffix dir.  do_listdir causes it to mistrust
    the hash cache for suffix existence at the (unexpectedly high) cost of a
    listdir.  reclaim_age is just passed on to hash_suffix. 

    :param partition_dir: absolute path of partition to get hashes for
    :param recalculate: 形如 recalculate=['a83']
      list of suffixes（后缀，即 hash值的后缀  310即为后缀  root@kinglion-Lenovo-Product:/srv/1/node/sdb1/objects/94238# ls
   310  hashes.pkl   ） which should be recalculated（又一次计算） when got
    :param do_listdir: force existence check for all hashes in the partition（对partion中的hashe强行运行检查）
    :param reclaim_age: age at which to remove tombstones 

    :returns: tuple of (number of suffix dirs hashed, dictionary of hashes)
    """

因没有传递recalulate这个參数故仅仅有do_listdir为True时会强制运行又一次计算后缀文件下全部文件名称字的hash值。文件名称字是时间戳，时间戳变了说明文件有更新，故须要和远程同步，检查是否为同一个版本号，不是同一个版本号的须要把本地版本号传递给远程server。

attempts_left = len(job['nodes'])
            #此时的nodes为除去本节点外的全部节点 由于 job['nodes]不包括本地节点get_more_nodes(int(job['partition']))能获得除去本partion所相应节点 外的其它全部节点
            nodes = itertools.chain(
                job['nodes'],
                self.object_ring.get_more_nodes(int(job['partition'])))

如上代码片段，attempts_left为当前job相应的分区去掉本地节点的其它的备份节点的个数。得到attempts_left后，下边接着更新了nodes，当中get_more_nodes方法会得到出去本分区所相应节点之外的其它全部节点的迭代器，全部nodes是除去本节点外全部节点的一个迭代器。

下边就是while循环，循环attempts_left次，

resp = http_connect(
                            node['replication_ip'], node['replication_port'],
                            node['device'], job['partition'], 'REPLICATE',
                            '', headers=self.headers).getresponse()

依据迭代得到的node请求，因副本节点首先被迭代到，故首先请求副本节点。若果成功请求读取resp返回的内容，得到远程设备同一个partion下的remote_hash

suffixes = [suffix for suffix in local_hash if
                                local_hash[suffix] !=
                                remote_hash.get(suffix, -1)]
                    #假设没有说明没有变动，则继续请求下一个节点
                    if not suffixes:
                        continue

对照两个设备同样partion下的hashes.pkl文件同样key而value不同的key。suffixes则说明和远程备份文件都是同一个版本号，继续请求下一个备份。假设不为空，则须要处理，同一时候再一次得到自己hashes.pkl目录中的内容，由于上一次请求时间中可能有其它的备份已经有新的更新推送到本server了。得到本地最新的hashes.pkl内容后再一次对照，得到不同的同样分区下的不同后缀

运行同步：

self.sync(node, job, suffixes)  #同步变化的

在同步变化时作者如今使用rsync方法，没有使用ssync，只是已经留出了ssync的实现，当ssync方法稳定时就会把rsync替换掉。（敬请期待）

 def sync(self, node, job, suffixes):  # Just exists for doc anchor point
        """
        Synchronize local suffix directories from a partition with a remote
        node.

        :param node: the "dev" entry for the remote node to sync with
        :param job: information about the partition being synced
        :param suffixes: a list of suffixes which need to be pushed

        :returns: boolean indicating success or failure
        """
        # self.sync_method = getattr(self, conf.get('sync_method') or 'rsync')
        #配置没有 sync_method方法 则运行类自己的rsync方法
        return self.sync_method(node, job, suffixes)

sync_method方法从例如以下获得，没有配置则运行rsync方法

self.sync_method = getattr(self, conf.get('sync_method') or 'rsync')

def rsync(self, node, job, suffixes):
        """
        Uses rsync to implement the sync method. This was the first
        sync method in Swift.
        """
        if not os.path.exists(job['path']):
            return False
        args = [
            'rsync',
            '--recursive',
            '--whole-file',
            '--human-readable',
            '--xattrs',
            '--itemize-changes',
            '--ignore-existing',
            '--timeout=%s' % self.rsync_io_timeout,
            '--contimeout=%s' % self.rsync_io_timeout,
            '--bwlimit=%s' % self.rsync_bwlimit,
        ]
        node_ip = rsync_ip(node['replication_ip'])
        #包括了ip信息
        if self.vm_test_mode:
            rsync_module = '%s::object%s' % (node_ip, node['replication_port'])
        else:
            rsync_module = '%s::object' % node_ip
        had_any = False
        for suffix in suffixes:
            spath = join(job['path'], suffix)
            if os.path.exists(spath):
                args.append(spath)
                had_any = True
        if not had_any:
            return False
        args.append(join(rsync_module, node['device'],
                    'objects', job['partition']))
        #args里面包括了通的全部信息 包括设备名称，设备分区
        return self._rsync(args) == 0

rsync方法将接受的參数都放到args中，然后运行_rsync方法。

    def _rsync(self, args):
        """
        Execute the rsync binary to replicate a partition.

        :returns: return code of rsync process. 0 is successful
        """
        start_time = time.time()
        ret_val = None
        try:
            with Timeout(self.rsync_timeout):
                #此处即为同步操作了，推送模式
                proc = subprocess.Popen(args,
                                        stdout=subprocess.PIPE,
                                        stderr=subprocess.STDOUT)
                results = proc.stdout.read()
                ret_val = proc.wait()
        except Timeout:
            self.logger.error(_("Killing long-running rsync: %s"), str(args))
            proc.kill()
            return 1  # failure response code
        total_time = time.time() - start_time
        for result in results.split('\n'):
            if result == '':
                continue
            if result.startswith('cd+'):
                continue
            if not ret_val:
                self.logger.info(result)
            else:
                self.logger.error(result)
        if ret_val:
            error_line = _('Bad rsync return code: %(ret)d <- %(args)s') % \
                {'args': str(args), 'ret': ret_val}
            if self.rsync_error_log_line_length:
                error_line = error_line[:self.rsync_error_log_line_length]
            self.logger.error(error_line)
        elif results:
            self.logger.info(
                _("Successful rsync of %(src)s at %(dst)s (%(time).03f)"),
                {'src': args[-2], 'dst': args[-1], 'time': total_time})
        else:
            self.logger.debug(
                _("Successful rsync of %(src)s at %(dst)s (%(time).03f)"),
                {'src': args[-2], 'dst': args[-1], 'time': total_time})
        return ret_val

当中例如以下代码片段就是运行详细的推送：

  #此处即为同步操作了，推送模式
                proc = subprocess.Popen(args,
                                        stdout=subprocess.PIPE,
                                        stderr=subprocess.STDOUT)

若job[delete]为True出现这样的情况的可能就是，因增删了设备，Ring 又一次调整，当前partion中的备份不再有此server的ID如partion号为45678的在rebalance前的对于的备份设备的id为[1,2,3]，假设当前设备id为1，则又一次rebalance后当前partion相应的备份为[4,2,3],则就会出现job[delete]为True的情况，我们看其代码详细实现：

    def update_deleted(self, job):
        """
        High-level method that replicates a single partition that doesn't
        belong on (不应放在 )this node.

        :param job: a dict containing info about the partition to be replicated
        """
        #得到parition下相应的后缀
        def tpool_get_suffixes(path):
            return [suff for suff in os.listdir(path)
                    if len(suff) == 3 and isdir(join(path, suff))]
        self.replication_count += 1
        self.logger.increment('partition.delete.count.%s' % (job['device'],))
        begin = time.time()
        try:
            responses = []
            suffixes = tpool.execute(tpool_get_suffixes, job['path'])
            if suffixes:
                for node in job['nodes']:
                    success = self.sync(node, job, suffixes)      #运行同步
                    if success:
                        with Timeout(self.http_timeout):
                            conn = http_connect(
                                node['replication_ip'],
                                node['replication_port'],
                                node['device'], job['partition'], 'REPLICATE',
                                '/' + '-'.join(suffixes), headers=self.headers)
                            conn.getresponse().read()
                    responses.append(success)
            if self.handoff_delete:
                # delete handoff if we have had handoff_delete successes
                delete_handoff = len([resp for resp in responses if resp]) >= \
                    self.handoff_delete
            else:
                # delete handoff if all syncs were successful
                delete_handoff = len(responses) == len(job['nodes']) and \
                    all(responses)
            #suffixes为空或 请求的三个已经都响应成功后删除本地partion下的文件
            if not suffixes or delete_handoff:
                self.logger.info(_("Removing partition: %s"), job['path'])
                tpool.execute(shutil.rmtree, job['path'], ignore_errors=True)
        except (Exception, Timeout):
            self.logger.exception(_("Error syncing handoff partition"))
        finally:
            self.partition_times.append(time.time() - begin)
            self.logger.timing_since('partition.delete.timing', begin)

至此 replicate操作就解说完成,文中若有理解不合理之处，请指正，谢谢！