How Google Works

by: Danny Sullivan

Email: seo@invancouver.com

Sometimes a search at Google might bring up different results if rerun just a few seconds later, here, understanding the dance part of the Google Dance name may be helpful. And to understand, let's flashback first to a different search engine, the AltaVista of old.

Back in the early days of AltaVista, all the pages that the search engine had resided in one big, powerful mainframe-style computer. Eventually, one computer wasn't enough, so the index was spread across four different mainframe computers. That helped with storage but not with query load. As a result, AltaVista made a duplicate copy of its index, a "mirror" which was kept in a different physical location.

As the system got more complicated, there was a greater chance that something could go wrong. For example, if one of AltaVista's four computers went down, then essentially 1/4 of its index was unavailable to any searchers who were unknowingly directed to that mirror. If they were suddenly switched to a different mirror when trying again, they might then hit the entire index and get different results.

Now let's fast-forward to Google today. Google (like other search engines) distributes its index across hundreds of computers with a processing power similar to that used on your desktop. That solves the storage problem. But what about query load? To help, Google has multiple copies of its index in various locations. When you search, you might hit a copy of the index located on the West Coast of the US, the East Coast or perhaps in Europe, to name some examples.

If the mirror you hit has a few of its computers down (which is fairly common), then some pages might not be available for searching. It's not as bad as in the old AltaVista days, because if 10 or 20 computers aren't working, that's a tiny amount compared to the hundreds that still are. Nevertheless, having some computers down at one mirror could cause the results to be slightly different if you get directed to a different mirror on your next search.

And now to the "dance" part. When Google updates its index, it has to spread the new information across these hundreds of computers in various locations. It generally takes a day or two until the new information is seeded and stable. As a results, some of the results may seem to "dance" around with slight changes, especially to webmasters who monitor positions like hawks.

So if you've done a search, then repeated it and gotten different results, two things are likely:

1. You may have hit a different mirror of the index on your repeat search where the copy isn't perfectly in line with the first index.


2. Second, and more likely, you've done a search and seen the Google Dance in action!

Website Link: http://www.searchenginewatch.com/_subscribers/articles/article.php/2216051

News Headlines

Archived News Items

No news items available at this time. Please check back soon.