使用一致性缓存的开销

Question

I consider caching key-value lists stored in database. Right now for rendering of JSF pages, a lot of redundant queries are executed to find the names to be displayed for some keys (O/R-Mapper: Eclipselink). The values are quasi-static, but can change very seldom by using the application (no change in database except by the application in question).

A simple cache would suffice when only using one application server. However, load balancing with multiple servers should be possible, avoiding returning stale values if data is changed using one server and therefore not reflected by the other server.

One idea would be to use oracle coherence as distributed cache. I'm not sure whether this is overkill because of the fact that the data is only changed very seldomly and the cache itself does not need to be distributed, only the invalidation should be.

What is the overhead of coherence in terms of memory, execution times and network communication? Are there any alternatives that better suit my use case?

I talk about 50.000 key value pairs, mainly short strings.

Answer 1

If the invalidation is that rare, then you can use a local cache and something like a JMS Topic that everyone subscribes to in order to handle the invalidation.

There's also something like EHCache as an alternative, since it's OSS and free to use vs Coherence, if that's important. I like to use EHCaches pull through ability.

Answer 2

Coherence has relatively low overhead, and can easily manage 50,000 (or 50,000,000) objects. However, if your use case is super simple, and you don't mind doing the invalidation work yourself, and don't need the various QoS that Coherence provides, then it probably is overkill.

Also, this simple use case can easily be done using the Coherence Standard Edition, which is far less expensive (licensed per server instead of per processor, and it's a much lower price).

For the sake of full disclosure, I work at Oracle. The opinions and views expressed in this post are my own, and do not necessarily reflect the opinions or views of my employer.