A spider trap is a situation in web crawling, where a web crawler ends up in an infinite loop, by repeatedly visiting the same pages again and again, or continuously discovering new, but irrelevant, pages.
Let us get a quick glance on this with below example.
Example 1: Infinite Loops
Suppose the web crawler is scanning a calendar application that presents the current month details and has links to "Next" and "Previous" months. This setup can create a spider trap, specifically an infinite loop trap for web crawlers.
How to address this infinite loop problem?
1. By Implementing a limit on how much depth (back or forward) the links go, e.g., only 8 to 10 level in either direction.
2. We can even tell the crawler that this page is not meant to crawl by adding below content to robots.txt file.
ser-agent: *
Disallow: /calendar/
3. By adding a "noindex" meta tag to the calendar pages, we can prevent them from being indexed by web crawlers.
<meta name="robots" content="noindex">
name="robots": This attribute specifies that the metadata is about robots, which are automated programs that crawl the web, like search engine crawlers.
content="noindex": This attribute specifies the instruction for the robots. In this case, "noindex" tells the crawler to not index the page, meaning the page won't show up in search results.
Example 2: Dynamically Generated Content Trap
Suppose you have a web page (/my-page/random-data) that generates new random data every time it is visited. This setup can create a spider trap known as a dynamic content trap.
In this example, the web crawler believes it is discovering new content on each visit, and this causes the crawler to repeatedly index the page, each time thinking it is indexing a different page.
We can notify crawler to not crawl these pages using robots.txt file and meta tags that we discussed in Example 1.
Another way is to look for patterns whether this content is really relevant, or some random data not meant to be indexed by crawler.
System Design Questions
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