是否有免费的 Java 缓存库可以提供统计信息并在重启时保留状态？

Question

[Edited] I am re-re-writing my question, hoping to be this time following the rules good questions and asking about a "narrowed enough" topic. I keep the information I initially provided, in case any reader is interested in details.

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My question:

I have been investigating free Java caching libraries and I found that all of them provide more or less the same features. But there are 2 tools that stand out over the rest, because they provide a distinctive feature:

• EHCache: Provides statistics for the cached elements. At any point you can get the metadata of each element, having access to details, such as the hit count - the number of times the entry was requested while it was in the cache.
• Infinispan: Provides a persistence-based mechanism to preserve cached data. This allows applications to not lose the cached elements on restart. Several persistence methods are supported, like database and filesystem.

I am wondering if there is another library that combines these 2 great features. Does anyone know about one?

Thank you.

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My original post:

I am working on a component that provides access to a reporting layer . Reports are generated on demand , but when a given report has been run the result (a Java object) can be cached and served again later if the same report is requested, without going again to the reporting engine.

I need to limit to " X " (configurable) the number of cached items. When the cache size has reached " X " elements and a new (not cached) report is requested I need to remove the " least-frequently-used " entry (LFU).

My component is notified when the reporting data changes in the data warehouse. In that case I need to:

• Figure out which ones are the " Y " " most-frequently-used " reports (being Y < X ).
• Invalidate the cache.
• Re-generate those reports through the reporting engine.
• Re-cache them.

These are all operations typically provided by most of the caching tools/libraries.

An additional requirement for me is that the cached reports must survive JVM restarts . This is, I cannot lose the information of which ones were the cached entries and I cannot re-generate them every time my application is restarted - because it would be too much load on the reporting engine.

My problem: I cannot find a free library that covers all my needs. In summary, these would be the required features:

• Free / commercial-friendly license.
• Persistent storage, saving state on JVM/server restart/crash.
• Java API, providing element statistics. I need to be able to "select the top X elements in cache" - using the eviction algorithm ranking as ordering.
• Easy to integrate with an application running on Tomcat.

The closest option I found is EHCache. It exposes the hit count for each element - but not the "real" ranking used by the eviction algorithm. Besides, persistent restartable mechanism is available only for a non-free version - BigMemory, from Terracotta.

Other alternative I have seen is Infinispan, but it does not expose entry-level statistics - only cache-level statistics - and requires JMX.

Answer 1

It sounds like what you are trying to do is create a document store that has functionality found in some caching frameworks, but itself isn't really a cache. I think you will have more luck finding the right solution by putting the idea of a cache to the side, and instead look at how you can build a persistent document store that has the functionality you require:

• Purging old documents
• Statistics about the documents being stored

As suggested by @djechlin, this is more of a design & architecture question that would be difficult to answer in this forum.

Best of luck.

Answer 2

Try Jboss' Cache: http://docs.jboss.org/jbossclustering/cluster_guide/5.1/html/jbosscache.chapt.html

it has eviction algorithm, persistent, it's free.