What Is a Cache on Facebook?by James T Wood
Facebook uses a massive cache of data about websites all over the Internet to make sharing faster and easier. When you post a link to your favorite blog or news site, Facebook will go to look at the cached information on its own servers before looking to the original site. This speeds up what happens on Facebook but it can introduce errors if the Facebook cache isn't up to date with the most recent content on the site referenced.
Facebook serves up a massive amount of data every second and that data needs to pass through its servers to get to the people checking status updates and liking pages. But when the data refers to something else on the Internet, Facebook first has to download the content, then turn around and upload it again to people looking at the Facebook site. To save time and resources, when content is downloaded once, it's cached -- or saved in a temporary, local file -- on Facebook's servers. This way, the content doesn't need to be downloaded before being sent on to the people looking at Facebook each time it's referenced.
Where caching really helps Facebook is in the sharing of links with video or images. That information can be quickly reposted and go viral, as you've probably seen on your Facebook feed when several people share the same link. But problems can come up when the original site is different from what Facebook has cached. This can happen if the link shared is to the main page of a blog and new posts have come up since the link was shared, for example. A reader clicking on the shared link won't see the right content because the Facebook cache is out of sync with the website.
Cache Handling Skills
When you share a link, you can help Facebook to determine how to handle it. Since each unique link is cached separately, Facebook can be tricked into creating a new cache by using a URL shortener like SnipURL, TinyURL or Dioop (see Resources) before posting the link to Facebook. This makes Facebook recache the URL and show the most recent content, but it will show up as separate from the original URL in terms of the number of shares the link gets on Facebook.
Facebook has provided a tool to help users see what is actually cached for each URL (see link in Resources). You can type a URL into the Facebook debugging tool and it will display the headline, images and other relevant data. This debugger has the added benefit of recaching a URL to Facebook's servers, so if you made changes and you don't want to use a different URL, you can reset the Facebook cache for a specific URL by running it through the Facebook URL debugging tool.