Outlook 2013 introduces hybrid cached mode

One of the nice things about attending the recent Microsoft Exchange Conference (MEC) is the chance to sit down with development engineers to learn about the software they’re working on. Karim Batthish introduced me to Allie Bellew because he wanted me to know about a new feature that’s coming in Outlook 2013. The problem that they are trying to solve is to provide users with quicker access to data when working in cached mode. As you might recall, Outlook 2013 changes its cached model to allow users to selectively keep a certain amount of data cached in the local OST while the remainder is held in the online mailbox. The theory here is that as we deal with larger and larger mailboxes, it does not make much sense to keep everything cached because users really only need access to their most recent data.

In any case, Outlook 2013 includes “hybrid mode”, which means that it’s got the ability to switch between cached and online data to display information to the user faster. The gate is 400ms, measured when the user logs on and connects to Exchange and updated when the user switches folders. If the network connection is good enough, Outlook can switch into hybrid mode to fetch data from the server and if not, access the OST.

The thought might cross your mind that it’s always going to be faster to access information from a local source, especially when the OST is held on a SSD. This is true: local cached information is always faster and Outlook prefers to get data from the OST whenever possible. But there are situations when the server has information that doesn’t exist in the OST because it simply hasn’t been synchronized to the client. Take the example of when you log on to Exchange first thing in the morning. It’s likely that the server has new messages waiting in the Inbox. Those messages are on the server but it will take time for Outlook to download them to populate the OST. Thus, it’s much faster (in user terms) to fetch the information from the server to allow the user to begin working with their new mail. Another example is when you install Outlook for the first time on a PC or create a new user profile. The next step in this process is to create the OST. Previous versions of Outlook can take a long time before they display any information downloaded from Exchange, but Outlook 2013 immediately realizes that no data exists in the OST and, if the network connection is good enough, fetches the data from the server.

Outlook 2013 switches from online to local access seamlessly. I was told that this doesn’t happen perfectly in the Outlook 2013 Preview version that Microsoft released in August, but works much better now, so much so that users shouldn’t realize any difference. And if the network connection disappears, Outlook 2013 will work like every other version since Outlook 2003 by depending on the data cached in the OST.

Hybrid mode doesn't depend on any particular version of Exchange. Although I've used it against Exchange 2013 and Office 365, I don't see any reason why it shouldn't work perfectly with Exchange 2007 and Exchange 2010 too.

Cached Exchange mode hasn’t seen any dramatic change since its introduction in Outlook 2003 some ten years go. It’s good to see an update now, especially one that just makes sense. Hybrid mode isn’t a secret because it was explained to MEC attendees who attended Allie’s session. It will be interesting to see how this feature is used when released!

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