This article wrote by PhilipSeo. I only want to share some information for everyone who don't know.

An insufficient Google crawl rate and incomplete indexation are the scourge of many websites, especially those large and new. In this forum and others, many members report indexation issues and ask how to solve them. The same is the case with SEO clients. My advice here is focused on Google, but the same general principles apply to crawling and indexation by Bing and Yahoo! as well....