There may be case when due to some terrible happening like database not performing, your web server return blank error pages 404 error. Perhaps the web server goes down altogether. In in the meanwhile, search engines are trying to index your pages, and donot find anything getting only blank pages.

In such cases the possibilities are:

1.If a server returns a 404, search engine will not list the web pages. If a search engine sees blank pages, or pages full of errors, it will not index the pages.This should be avoided at any costs.

2. However, not finding anything i.e no connection. This is actually more desirable than it sounds in terms of indexing.

Although it may look extremely unprofessional, a search engine is likely to assume that there are intermittent connectivity problems and try again later. Your users may, however,be annoyed. At least from a bot point of view, though, as long as this is resolved in a day or so, there is no major issues. A “500” status code can be returned, along with some custom page describing the error. This indicates to search engines that there is a temporary technical problem. Perhaps the site is down for maintenance. Say it politely and provide the time it will be back up. So one can put up a global error page for every URL. To do this in PHP use this line of PHP, and then add custom content as you wish: