官方文档

The RetryMiddleware can be configured through the following settings (see the settings documentation for more info):

• RETRY_ENABLED

• RETRY_TIMES

• RETRY_HTTP_CODES

源码(以版本V2.5为例)

class RetryMiddleware:

    # IOError is raised by the HttpCompression middleware when trying to
    # decompress an empty response
    EXCEPTIONS_TO_RETRY = (defer.TimeoutError, TimeoutError, DNSLookupError,
                           ConnectionRefusedError, ConnectionDone, ConnectError,
                           ConnectionLost, TCPTimedOutError, ResponseFailed,
                           IOError, TunnelError)

    def __init__(self, settings):
        if not settings.getbool('RETRY_ENABLED'):
            raise NotConfigured
        self.max_retry_times = settings.getint('RETRY_TIMES')
        self.retry_http_codes = set(int(x) for x in settings.getlist('RETRY_HTTP_CODES'))
        self.priority_adjust = settings.getint('RETRY_PRIORITY_ADJUST')

    @classmethod
    def from_crawler(cls, crawler):
        return cls(crawler.settings)

    def process_response(self, request, response, spider):
        if request.meta.get('dont_retry', False):
            return response
        if response.status in self.retry_http_codes:
            reason = response_status_message(response.status)
            return self._retry(request, reason, spider) or response
        return response

    def process_exception(self, request, exception, spider):
        if (
            isinstance(exception, self.EXCEPTIONS_TO_RETRY)
            and not request.meta.get('dont_retry', False)
        ):
            return self._retry(request, exception, spider)

    def _retry(self, request, reason, spider):
        max_retry_times = request.meta.get('max_retry_times', self.max_retry_times)
        priority_adjust = request.meta.get('priority_adjust', self.priority_adjust)
        return get_retry_request(
            request,
            reason=reason,
            spider=spider,
            max_retry_times=max_retry_times,
            priority_adjust=priority_adjust,
        )

解读

解读源码发现RetryMiddleware 主要有以下功能

1. 出现网络，连接相关异常时重试
2. 出现指定的状态码< RETRY_HTTP_CODES >时重试;
   最大重试次数为< RETRY_TIMES >;
   且重试请求可以调整优先级< RETRY_PRIORITY_ADJUST >;
   默认不修改优先级