【Patroni源码阅读】使用pg_basebackup创建副本

basebackup.py

class Bootstrap(object):
    def basebackup(self, conn_url, env, options):
        # creates a replica data dir using pg_basebackup.
        # this is the default, built-in create_replica_methods
        # tries twice, then returns failure (as 1)
        # uses "stream" as the xlog-method to avoid sync issues
        # supports additional user-supplied options, those are not validated
        maxfailures = 2
        ret = 1
        # 禁止用户传递的参数
        not_allowed_options = ('pgdata', 'format', 'wal-method', 'xlog-method', 'gzip',
                               'version', 'compress', 'dbname', 'host', 'port', 'username', 'password')
        user_options = self.process_user_options('basebackup', options, not_allowed_options, logger.error)

        for bbfailures in range(0, maxfailures):
            if self._postgresql.cancellable.is_cancelled:
                break

            # pg_basebackup运行前需要清空数据目录
            if not self._postgresql.data_directory_empty():
                self._postgresql.remove_data_directory()
            try:
                ret = self._postgresql.cancellable.call([self._postgresql.pgcommand('pg_basebackup'),
                                                         '--pgdata=' + self._postgresql.data_dir, '-X', 'stream',
                                                         '--dbname=' + conn_url] + user_options, env=env)
                if ret == 0:
                    break
                else:
                    logger.error('Error when fetching backup: pg_basebackup exited with code=%s', ret)

            except Exception as e:
                logger.error('Error when fetching backup with pg_basebackup: %s', e)

            if bbfailures < maxfailures - 1:
                logger.warning('Trying again in 5 seconds')
                time.sleep(5)

        return ret