If a page is updated less frequently, then it is rude to burden the pages server with repeated crawl requests and hence it is only polite to ease the burden on the crawlers to crawl the page unnecessarily.With the need to be present on the search engine bots listing, each page is in a race to get noticed by optimizing its content and curating data to align with the crawling bots algorithms.Hence, to bridge this need gap, web crawlers came into existence.
It is essential for the crawlers to evolve at the same pace as internet is involving in the current scenario. Website Crawler Tool Code Snippets CanIn order to support this evolution, each crawler should get their basic layout right, so new features and code snippets can be extended upon the same crawler. Following is the basic functionality layout how the crawlers should work. The crawler would then follow its inbuilt traversing algorithm via which it shall crawl the connected sets of pages and their nodes horizontally or vertically. Nowadays, most of the websites have a sitemap.xml file with a list of all URLs present on the website, to help the search engine bots discover all pages on visit. Then it needs to check if various urls from a page need to be crawled, it is often based on update frequency of the site(Sidenote this is why if you update your site more often, so search engines crawl it more often). Once the URLs to be crawled have been shortlisted, All the URLs that need to be crawled are pushed into the queue that follows a LIFOFIFO pattern depending upon the crawlers algorithm and the URLs are removed as and when they get crawled. In most such setup from technical point of view, queue comes as a handy tool to simplify the architecture of the whole system. After that crawler goes and gets the page and saves it on local machine. Actual fetching of the pages in laymans terms is similar to going on a webpage and then doing a Right click save. If the site is more interactive have lot of AJAX interactions, then bots have to be more advancedcustom to get the data.After fetching the data, which is then stored separately for extraction and structuring. Hence it is not feasible to store all these URLs in the queue manually or even mechanically for that matter. Thus each time a crawler is developed, it is essential to add the Discover function in the web crawler code. This way, you can train a crawler to discover URLs by itself that need to be crawled by hopping from one seed URL to the connecting URL and so forth. Now a days, the way webpages are linked and interlinked, bots go from one page to another. However, if there are standalone pages(silos), which neither link to other pages nor are linked from other pages, they are difficult to discover. So webmasters take extra care to put them in sitemap.xml or add the link for them somewhere on the site so that search engines can reach them easily. In order to avoid recrawling these pages and prevent the crawler from going into a loop, it is essential to perform a deduplication check before crawling a page. If that page has already been crawled, you can push that page to the seed list to make further discovery of pages easier. Hence, while crawling a page, we run another check to see the last time stamp when that page was updated, per crawl. In case a page is updated more frequently, then it makes sense to crawl that page regularly to identify and report the changes accordingly.
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