AppFabric Syncing Local Caches

Question

We have a very simple AppFabric setup where there are two clients -- lets call them Server A and Server B. Server A is also the lead cache host, and both Server A and B have a local cache enabled. We'd like to be able to make an update to an item from server B and have that change propagate to the local cache of Server A within 30 seconds (for example).

As I understand it, there appears to be two different ways of getting changes propagated to the client:

1. Set a timeout on the client cache to evict items every X seconds. On next request for the item it will get the item from the host cache since the local cache doesn't have the item
2. Enable notifications and effectively subscribe to get updates from the cache host

If my requirement is to get updates to all clients within 30 seconds then setting a timeout of less than 30 seconds on the local cache appears to be the only choice if going with option #1 above. Due to the size of the cache, this would be inefficient to evict all of the cache (99.99% of which probably hasn't changed in the last 30 seconds).

I think what we need to implement is option #2 above, but I'm not sure I understand how this works. I've read all of the msdn documentation (http://msdn.microsoft.com/en-us/library/ee808091.aspx) and have looked at some examples but it is still unclear to me whether it is really necessary to write custom code or if this is only if you want to do extra handling.

So my question is: is it necessary to add code to your existing application if want to have updates propagated to all local caches via notifications, or is the callback feature just an bonus way of adding extra handling or code if a notification is pushed down? Can I just enable Notifications and set the appropriate polling interval at the client and things will just work?

It seems like the default behavior (when Notifications are enabled) should be to pull down fresh items automatically at each polling interval.

Answer 1

I ran some tests and am happy to say that you do NOT need to write any code to ensure that all clients are kept in sync. If you set the following as a child element of the cluster config:

In the client config you need to set sync="NotificationBased" on the element.

The element in the client config will tell the client how often it should check for new notifications on the server. In this case, every 15 seconds the client will check for notifications and pull down any items that have changed.

I'm guessing the callback logic that you can add to your app is just in case you want to add your own special logic (like emailing the president every time an item changes in the cache).