Set Preferred Domain (http:// or http://www.)

Google ask your preferred domain in webmaster. Preferred domain is one which you like to appear on search result page. Google will try to index your site according to preferred domain of your choice. So, web site satya-weblog.com can appear as http://satya-weblog.com or http://www.satya-weblog.com. I have set my preferred domain as http://www.satya-weblog.com.

Link may point to any domain (www or non www) version of web site, but Google will take into consideration whatever your preference and index your web site as your specified preference next time it crawl your blog. This setting does not mean that your all pages on web site will be indexed or whatever. It only means that Google will keep in mind when it index any page. Google index pages based on keyword relevancy, traffic and  traffic possibility of a page. Important: Google will treat www.example.com and http://www.example.com as separate domain if you do not mention you preferred domain. So, it may affect your ranking, because http://www.satya-weblog.com/tag/javascript and http://satya-weblog.com/tag/javascript will be treated as two different pages.

Once you set your preferred domain, you should redirect 301 (permanent redirect), to tell Google and other search engine what you prefer. This will result in better credit of search ranking to your pages.

Page: https://www.google.com/webmasters/tools/settings:

WebMaster Preferred domain

WebMaster Preferred domain

In the image "Geographic target=Unlisted" tells the Google that my site is not targeted for geographic location. It is global and for all.
Crawl rate setting may be different for you. Set custom crawl rate option appear only for good traffic site.

Reference:Google WebMaster

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