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How Google discovers pages (crawling) in SEO Fundamentals - Performance & Efficiency

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Time Complexity: How Google discovers pages (crawling)
O(n)
Understanding Time Complexity

When Google finds new web pages, it uses a process called crawling. Understanding how long this takes helps us see how quickly new content appears in search results.

We want to know how the time to discover pages grows as the number of pages increases.

Scenario Under Consideration

Analyze the time complexity of this simplified crawling process.


// Start with a list of known URLs
queue = [seed_url]
visited = set()

while queue:  # corrected syntax
  current_url = queue.pop()
  if current_url not in visited:
    visited.add(current_url)
    links = extract_links(current_url)
    for link in links:
      if link not in visited:
        queue.append(link)

This code visits pages, extracts links, and adds new pages to visit until all reachable pages are found.

Identify Repeating Operations

Look at what repeats as the crawler runs:

  • Primary operation: Visiting each page and extracting its links.
  • How many times: Once for each unique page found.
How Execution Grows With Input

As the number of pages grows, the crawler visits more pages and extracts more links.

Input Size (n)Approx. Operations
10About 10 page visits and link checks
100About 100 page visits and link checks
1000About 1000 page visits and link checks

Pattern observation: The work grows roughly in direct proportion to the number of pages found.

Final Time Complexity

Time Complexity: O(n)

This means the time to crawl grows linearly with the number of pages discovered.

Common Mistake

[X] Wrong: "Crawling time grows much faster because every page links to every other page."

[OK] Correct: In reality, each page is visited once, so the crawler does not repeatedly visit the same pages, keeping growth linear.

Interview Connect

Understanding how crawling scales helps you think about real systems that handle lots of data efficiently. This skill shows you can reason about processes that grow with input size.

Self-Check

"What if the crawler revisited pages multiple times instead of tracking visited ones? How would the time complexity change?"

Practice

(1/5)
1. What is the main method Google uses to discover new web pages?
easy
A. Guessing URLs based on popular keywords
B. Manually adding pages submitted by users
C. Waiting for website owners to email URLs
D. Using automated crawlers that follow links from known pages

Solution

  1. Step 1: Understand Google's discovery process

    Google uses automated programs called crawlers or spiders to find new pages by following links from pages it already knows.

  2. Step 2: Compare options

    Only Using automated crawlers that follow links from known pages describes this automated crawling method. Other options describe manual or guessing methods which Google does not rely on.

  3. Final Answer:

    Using automated crawlers that follow links from known pages -> Option D

  4. Quick Check:

    Google uses crawlers = A [OK]
Hint: Remember: Google bots crawl links automatically [OK]
Common Mistakes:
  • Thinking Google manually adds pages
  • Believing Google guesses URLs randomly
  • Assuming email submissions are main method
2. Which of the following is the correct term for Google's automated program that finds new pages?
easy
A. Crawler
B. Indexer
C. Ranker
D. Optimizer

Solution

  1. Step 1: Identify Google's discovery tool name

    The program Google uses to find new pages by following links is called a crawler or spider.

  2. Step 2: Eliminate other terms

    Indexer organizes pages after crawling, Ranker orders results, Optimizer improves site SEO. Only Crawler finds pages.

  3. Final Answer:

    Crawler -> Option A

  4. Quick Check:

    Google's discovery tool = Crawler [OK]
Hint: Crawler = program that finds pages [OK]
Common Mistakes:
  • Confusing crawler with indexer
  • Thinking ranker finds pages
  • Mixing optimizer with crawler
3. If a website has no links from other sites and no sitemap, what will likely happen when Google tries to discover its pages?
medium
A. Google will find the pages quickly by guessing URLs
B. Google will automatically add the pages to its index
C. Google will not find the pages easily because there are no links or sitemap
D. Google will send a manual request to the website owner

Solution

  1. Step 1: Understand how Google discovers pages

    Google relies on links and sitemaps to find new pages. Without these, discovery is difficult.

  2. Step 2: Analyze options

    Google will not find the pages easily because there are no links or sitemap correctly states Google won't find pages easily without links or sitemap. Other options describe guessing, automatic adding, or manual requests which do not happen.

  3. Final Answer:

    Google will not find the pages easily because there are no links or sitemap -> Option C

  4. Quick Check:

    No links or sitemap = hard to find pages [OK]
Hint: No links or sitemap means hard for Google to find pages [OK]
Common Mistakes:
  • Assuming Google guesses URLs
  • Thinking Google adds pages automatically
  • Believing Google contacts owners manually
4. A website owner notices Google is not discovering some new pages. Which of these is a likely cause?
medium
A. The new pages are not linked from any other page on the site
B. The website has a sitemap listing all pages
C. The pages have clear, descriptive titles
D. The website uses HTTPS protocol

Solution

  1. Step 1: Identify why Google misses pages

    Google finds pages by following links. If new pages are not linked anywhere, crawlers cannot find them.

  2. Step 2: Evaluate other options

    Sitemap helps discovery (B), titles help ranking (C), HTTPS helps security (A). Only lack of links (D) blocks discovery.

  3. Final Answer:

    The new pages are not linked from any other page on the site -> Option A

  4. Quick Check:

    No links = no discovery [OK]
Hint: Pages must be linked or in sitemap to be found [OK]
Common Mistakes:
  • Thinking HTTPS affects discovery
  • Confusing titles with discovery
  • Ignoring importance of internal links
5. You want Google to discover a new section of your website quickly. Which combination of actions will help the most?
hard
A. Change the website's color scheme and add meta descriptions
B. Add internal links to the new pages and submit an updated sitemap
C. Remove old pages and increase page load speed
D. Use HTTPS and add social media share buttons

Solution

  1. Step 1: Identify key factors for fast discovery

    Google discovers pages by crawling links and reading sitemaps. Adding internal links and updating sitemap helps crawlers find new pages quickly.

  2. Step 2: Analyze other options

    Changing colors or meta descriptions (B) does not affect discovery speed. Removing old pages or speed (C) helps ranking but not discovery. HTTPS and social buttons (D) improve security and sharing but not crawling.

  3. Final Answer:

    Add internal links to the new pages and submit an updated sitemap -> Option B

  4. Quick Check:

    Links + sitemap = faster discovery [OK]
Hint: Links plus sitemap speed up Google discovery [OK]
Common Mistakes:
  • Focusing on design changes instead of links
  • Ignoring sitemap importance
  • Confusing ranking factors with discovery