Velocity: Microsoft distributed memory cache

In the past few years, distributed memory cache applications have become quite popular, from mainstream Java applications to edge languages like Erlang. To continue to catch up with the dominant technology in the Open Source world, Microsoft also introduced its distributed cache.

Velocity is a distributed cache designed specifically for the. NET platform. Those who are familiar with other distributed memory caches will find many similar features. It is currently available for external download as a Community Technology preview.

There are two types of velocity clients. A simple client only knows one single cache server. If the requested object is not found on that server, the cache server will fetch it from the appropriate server. The routing client is more familiar with it. They always know where to find a special object, so they can directly query the cache server. The impact of sending data from all cached locations to the routing client on performance has not yet been determined. Besides the cache server, both types of clients support a local cache option. For expired data, this option still requires checking the server. However, when processing a large number of cached objects, it should reduce network traffic.

There are two options for concurrency. With optimistic concurrency, only the first update can be successful. Any subsequent update of existing expired objects will fail. When a pessimistic lock is used, a Lock handle is returned. Before the lock is released or timed out, any attempt to obtain the lock will fail. Failed lock acquisition is a non-blocking operation.

Objects can be explicitly removed from the cache by setting an expiration date or when the memory pressure is too high. The latter method, called eviction, uses the least recently used algorithm for processing.

In addition to a keyword, an object may have a group of associated tags. Velocity allows you to retrieve one or all objects that match a tag list.

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