Windows Azure Cache - What are regions and tags and how we can used them

In the last post we talked about the new in-memory cache from Windows Azure. In this post I would like to talk about what are regions and tags.
For what we know until now, we can define one or more named cache in the same cache “server”. Based on the cache name, we can point to that cache and used it. At this point you should know that we have a limit of 128 named cached for a given server. But I think that this number of named cache per deployment is enough for almost all scenarios.
Each named cache can contains an “unlimited” number of regions. You can image a region as a container in a named cache. A named cache doesn’t need to contain a region. We need explicit create a region in a given named cache.
Very important, because a region group cache items, a region is limited to a single cache host. Because of this regions are not supported in Windows Azure Shared Caching.
Each item added to a region can contain a tag. Normally, an object that is added to a cache (without being added to a region) can be accessed only by the key – we will not be able to search for an item in the cache. An item that was tagged need to be added to a specific region. Based on the tags object from a region can be searched. This functionality is available only when we use regions and tags.
In the next example we will create a region and add two items to that region. It is very important to know that an item from cache can have 0 to n tags.

DataCache dc = new DataCache(“fooCache”);
dc.CreateRegion(“myRegion”);
dc.Put(
“itemKey1”,
“Iris”,
new List<DataCacheTag>()
{
       new DataCacheTag(“music”),
       new DataCacheTag(“europe”),

},
“myRegion”);
dc.Put(
“itemKey2”,
“Microsoft”,
new List<DataCacheTag>()
{
       new DataCacheTag(“IT Company”),
       new DataCacheTag(“europe”),

},
“myRegion”);

In this moment in the “myRegion” region we have two items. It we will search for items in this region that have the tag “europe” we will find two items.

KeyValuePair<string, object> itemsWithTagEurope =
    dc.GetObjectByTag( new DataCacheTag(“europe”), “myRegion”);

When to use this feature? When we need to search items from cache based on specific tags. For example we could have some items in the cache that could have some key words (an article from a newspaper can have some keywords). In this case we would like to retrieve an article from a specific country that has a given tag. The country can be represented by a region from the cache. And each article link from the cache could have some tags (keywords).
This was all about regions and tags from in-memory cache. This is a powerful feature that can be used in situations when we need to retrieve items from the cache not only based on the key.