The crawler creates periodically so called breakpoints. When doing so, the current state of the search index is copied into a separate directory called breakpoint. If the index update should be cancelled (e.g. if the computer is shut down), the crawler will go on from the last breakpoint the next time it is started and doesn't have to start at the beginning.

By default breakpoints are created every 10 minutes. You can change the interval or disable breakpoints using the <breakpointInterval> tag in the CrawlerConfiguration.xml.