AMP is short for "Accelerated Mobile Pages". AMP is a Google-run website publishing technology. AMP pages can be displayed in most current browsers. AMP pages served in Google search typically load in less than one second and use 10 times less data than the equivalent non-AMP pages.

Critics see AMP as an attempt by Google to exert its dominance on the Web by dictating how websites are built and monetized.

Crawling and indexing an AMP page is the same as crawling and indexing a regular web page. However, if you have AMP errors, especially around required markup, it will affect the success of your AMP pages being crawled.

Google crawls and indexes AMP pages at the same rate as regular pages. Ensure AMP documents are valid to increase successful crawl of the AMP pages.

Home pages and product detail pages go through the same indexing flow. Google uses various factors, such as how often we've seen a page's primary content change, to determine the optimal crawl frequency on a per-page basis.

While crawling is generally required for indexing and ranking, forcing a page to be recrawled more often doesn't affect its indexing or ranking.

Google generally doesn’t distinguish product category page or product description page for search, but for example, category page may lead to the discovery of new product description pages.

Beware that dynamically generated product listing pages can easily become "infinite spaces" that make crawling harder than necessary.

Yes, it's fine to have page types that change frequently, such as auction items or classified ads that have a limited life-time. A site can give Google information on new & updated pages using sitemap files.

If you need to make changes often, use the Google AMP cache update-cache request.

Advertisement campaigns do not influence indexing or ranking of pages in Google's organic search results.

Webmasters can help Googlebot by providing sitemaps, or, for individual URLs only, by submitting them through Search Console.

Adopting AMP doesn’t change ranking. Google Search is using using mobile speed as a ranking factor, but sites can be fast by using a variety of techniques, including AMP. That is, Google Search applies the same standard to all pages, regardless of the technology used to build the page.

A small percentage itself is not a problem. Use Search Console to get a rough understanding of the number of AMP pages found on your site. Check "Accelerated Mobile Pages" under "Search Appearance".

Google Search may not have discovered all of the AMP pages on your site. This is normal and will improve over time, as Google discovers the AMP pages. We recommend using sitemaps to notify Google of new and updated pages.

Googlebot tries to not cause problems for your site's serving infrastructure. It limits crawling based on how your site responds. It tries to prioritize in crawling and indexing most useful pages on your site. More information on prioritization of crawling.

Google may not see links between AMP and its canonical such as when, for example, the amphtml link of the canonical page or the link to the canonical from AMP is broken. When these two documents can't be paired, they may be treated as separate documents.

In the scenario of the question, where there is a desktop site and a mobile AMP site, AMP should point to desktop with <<link rel="canonical">, Desktop should point to AMP with <link rel="amphtml">.

AMP can also be stand-alone canonical that serves all traffic. In many cases, there's no need to have separate desktop or mobile (m.) sites. If for some reason, all three of desktop, mobile, and AMP exist:

• Desktop: point to AMP with <link rel="amphtml"> and to mobile with rel=alternate
• Mobile: point to desktop with <link rel="canonical"> and to AMP with rel=amphtml (mobile should be equivalent in content to desktop)
• AMP: point to desktop with <link rel="canonical">

Adding structured data to your content may make your page eligible to appear in carousels and rich results. However, being eligible for a certain Search feature doesn’t guarantee display of that feature.

Here are some other possible reasons your page isn’t surfacing in the top stories carousel:

• The page hasn’t been indexed.
• The page didn’t make it to the carousel: There is no guarantee that your page will appear in Search results as a specific feature. This is because search features depend on many factors, including the search device type, location, and whether Google thinks the feature would provide the best search experience for the user.
• The page isn't a valid AMP page.

Yes. Googlebot has to crawl all the documents, including AMP, within a server's crawl budget to avoid causing issues on your site. In general, most websites don't need to worry about the crawl budget, and AMP content is very efficient to be crawled and indexed.

When a modern search robot crawls a page, it also needs to fetch sub resources, like JavaScript, CSS, images, etc. to fully understand the page. The number of sub resources is a lot greater than the main document (according to HTTP Archive, the average number of requests on a site is over 100.). AMP pages generally require fewer resources.