Scrapy - set delay to retry middleware

Question

I\'m using Scrapy-splash and I have a problem with memory. I can clearly see that memory used by docker python3 is gradually increasin

Answer 1

Method 1

One way would be to add a middleware to your Spider (source, linked):

# File: middlewares.py

from twisted.internet import reactor
from twisted.internet.defer import Deferred


class DelayedRequestsMiddleware(object):
    def process_request(self, request, spider):
        delay_s = request.meta.get('delay_request_by', None)
        if not delay_s:
            return

        deferred = Deferred()
        reactor.callLater(delay_s, deferred.callback, None)
        return deferred

Which you could later use in your Spider like this:

import scrapy


class QuotesSpider(scrapy.Spider):
    name = "quotes"
    custom_settings = {
        'DOWNLOADER_MIDDLEWARES': {'middlewares.DelayedRequestsMiddleware': 123},
    }

    def start_requests(self):
        # This request will have itself delayed by 5 seconds
        yield scrapy.Request(url='http://quotes.toscrape.com/page/1/', 
                             meta={'delay_request_by': 5})
        # This request will not be delayed
        yield scrapy.Request(url='http://quotes.toscrape.com/page/2/')

    def parse(self, response):
        ...  # Process results here

Method 2

You could do this with a Custom Retry Middleware (source), you just need to override the process_response method of the current Retry Middleware:

from scrapy.downloadermiddlewares.retry import RetryMiddleware
from scrapy.utils.response import response_status_message


class CustomRetryMiddleware(RetryMiddleware):

    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)

            # Your delay code here, for example sleep(10) or polling server until it is alive

            return self._retry(request, reason, spider) or response

        return response

Then enable it instead of the default RetryMiddleware in settings.py:

DOWNLOADER_MIDDLEWARES = {
    'scrapy.downloadermiddlewares.retry.RetryMiddleware': None,
    'myproject.middlewarefilepath.CustomRetryMiddleware': 550,
}

Answer 2

1. A more elaborate solution could be to set up a Kubernetes cluster in which you have multiple replicas running. This way you avoid having a failure of just 1 container impacting your scraping job.

2. I don't think it's easy to configure a waiting time only for retries. You could play with DOWNLOAD_DELAY (but this will impact delay between all requests), or set the RETRY_TIMES to a higher value than the default of 2.