title: Info on Scrapy CONCURRENT_REQUESTS
body: <p>I'm using Scrapy and I read on the doc about the setting &quot;CONCURRENT_REQUESTS&quot;. The docs talk about &quot;The maximum number of concurrent (ie. simultaneous) requests that will be performed by the Scrapy downloader.&quot;</p>
  <p>I created a spider in order to take questions and answers from Q&amp;A websites, so I want to know if is possible run multiple concurrent requests.
  Now I have set this value to 1 because I don't want to lose some Item or override someone.</p>
  <p>The <strong>main doubt</strong> is that I have a Global ID <code>idQuestion</code> (for making an <code>idQuestion.idAnswer</code>) for any item so I don't know if making multiple requests all can be a mess and lose some Item or set wrong Ids.</p>
  <p>This is a snippet of code:</p>
  <pre><code>class Scraper(scrapy.Spider):
      uid = 1
  
  
      def parse_page(self, response):
          # Scraping a single question
  
          item = ScrapeItem()
          hxs = HtmlXPathSelector(response)
          #item['date_time'] = response.meta['data']
          item['type'] = &quot;Question&quot;
          item['uid'] = str(self.uid)
          item['url'] = response.url
  
          #Do some scraping.
          ans_uid = ans_uid + 1
          item['uid'] = str(str(self.uid) + (&quot;:&quot; + str(ans_uid)))
          yield item
  
          #Call recusivly the method on other page.
          print(&quot;NEXT -&gt; &quot;+str(composed_string))
          yield scrapy.Request(composed_string, callback=self.parse_page)
  </code></pre>
  <p>This is the skeleton of my code.
  I use uid to memorize the id for the single question and ans_uid for the answer.</p>
  <p>Ex:</p>
  <ol>
  <li>Question</li>
  </ol>
  <p>1.1) Ans 1 for Question 1</p>
  <p>1.2) Ans 2 for Question 1</p>
  <p>1.3) Ans 3 for Question 1</p>
  <p><strong>Can I simply increase the CONCURRENT_REQUESTS value without compromising anything?</strong></p>