Understanding the Mechanics of Google's Web Crawling

A web crawler is essentially an automated program that systematically navigates the internet, discovering and scanning web pages. In the realm of Google, its crawler serves a dual purpose: 

Link Exploration and Page Importance: 

Google's crawler meticulously follows links embedded within webpages, recursively crawling through the interconnected network of pages. This process allows Google to build an extensive collection of pages. The crawler also evaluates the significance of a webpage by counting the number of times it is linked to, employing an algorithm known as PageRank. 

Indexing Content: 

The words present on a webpage are added to Google's index. Analogous to an index in a book, this compilation indicates which web pages contain the words users might search for. When a user initiates a search, Google can swiftly retrieve relevant information from its index, a far more efficient process compared to scanning every webpage in real-time. 

It's essential to note that this overview is a simplification of the intricate procedures occurring behind the scenes. Google's search algorithms involve tasks such as ranking pages, correcting spelling errors, identifying and blocking malicious content, and handling complex queries with special operators. 

Despite the perception of Google having boundless resources, the reality is that the crawling interval for the entire web is constrained by factors such as crawling bandwidth. To shed light on this, let's delve into some figures. 

Google, while keeping its crawl frontier size a secret, hinted in 2008 that they were aware of approximately 1 trillion URLs. This figure likely represents the scope of pages they are aware of rather than those crawled regularly. Assuming today's crawl frontier size is around 1 trillion, we can explore the data dimensions. 

The average size of web pages has increased to 1600KB, but considering elements like media and ads, let's assume Google fetches an average of 400KB per page. This results in a staggering 400,000 terabytes (TB) or 400 petabytes (PB) of data that Google needs to access to crawl the entire web. 

The challenge lies in the speed at which Google can accomplish this feat. In 2014, global IP traffic reached approximately 61 exabytes per month. To crawl the entire web twice a month, Google would need to utilize only 1.31% of this traffic. While the cost of bandwidth is not a significant concern for Google, the sheer volume of data—400PB—requires careful consideration. 

With a hypothetical 10 terabits per second bandwidth, it would take Google around 4 days to crawl everything. However, to crawl the entire web daily, they would need about 18% of the entire global IP traffic. This presents a logistical challenge, indicating that Google likely takes a few weeks to complete a comprehensive crawl, with variations in the speed of crawling for different segments of the web. 

In Short:

As with any estimates, these numbers are rough approximations, offering valuable insights into the complexities of Google's web crawling endeavors. Precise figures from Google would undoubtedly provide a more detailed understanding of their monumental task.