Friday, 20 September 2013

Heterogenous clusters with Infinispan 6.0.0.Beta1

One of the basic rules of participating in an Infinispan cluster was that everyone must pay their fair share. Sure, each node was able to run a diferent set of caches (i.e. the cluster didn't have to be symmetric). But when a node started up a distributed cache, it automatically took ownership of a share of the keys equal to all the other members of the cache.

With the implementation of ISPN-3051 in 6.0.0.Beta1, that is no longer the case. Each node can now opt to own more or less keys, using the new capacityFactor setting. The default capacity factor is 1.0, and nodes can specify both a higher and a lower value via configuration API:

Or via the XML configuration:
Note that we don't guarantee that the number of keys owned by a node will be exactly proportional to its capacity factor. In particular, custom ConsistentHashFactory implementations are free to ignore the capacityFactor setting completely. But the default ConsistentHashFactory will try to respect it as much as it can.

One interesting use case is nodes with a capacity factor of 0. This could be useful when some nodes are too short-lived to be useful as data owners, but they can't use HotRod (or other remote protocols) because they need transactions. With cross-site replication as well, the "site master" should only deal with forwarding commands between sites and shouldn't handle user requests, so it makes sense to configure it with a capacity factor of 0.

A final note: Infinispan server 6.0.0.Beta1 also supports this feature, but the setting is called capacity-factor to match the AS naming convention.

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