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POIs there a free Java caching library that provides statistics and preserves state on restart?
 

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  1. POIs there a free Java caching library that provides statistics and preserves state on restart?
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    <p><em>[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.</em></p> <hr> <p><em><strong>My question:</em></strong></p> <p>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:</p> <ul> <li>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.</li> <li>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.</li> </ul> <p>I am wondering if there is another library that combines these 2 great features. Does anyone know about one?</p> <p>Thank you.</p> <hr> <p><em><strong>My original post:</em></strong></p> <p>I am working on a component that <em>provides access to a reporting layer</em>. Reports are generated <strong>on demand</strong>, but when a given report has been run the result (a Java object) <strong>can be cached</strong> and served again later if the same report is requested, without going again to the reporting engine.</p> <p>I need to limit to "<strong>X</strong>" (configurable) the number of cached items. When the cache size has reached "<strong>X</strong>" elements and a new (not cached) report is requested I need to remove the "<strong>least-frequently-used</strong>" entry (LFU).</p> <p>My component is notified when the reporting data changes in the data warehouse. In that case I need to:</p> <ul> <li>Figure out which ones are the "<strong>Y</strong>" "<strong>most-frequently-used</strong>" reports (being <strong>Y &lt; X</strong>).</li> <li>Invalidate the cache.</li> <li>Re-generate those reports through the reporting engine.</li> <li>Re-cache them.</li> </ul> <p>These are all operations typically provided by most of the caching tools/libraries.</p> <p>An additional requirement for me is that the cached reports <strong>must survive JVM restarts</strong>. 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.</p> <p><strong>My problem:</strong> I <em>cannot find</em> a <strong>free</strong> library that covers all my needs. In summary, these would be the required features:</p> <ul> <li>Free / commercial-friendly license.</li> <li>Persistent storage, saving state on JVM/server restart/crash.</li> <li>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.</li> <li>Easy to integrate with an application running on Tomcat.</li> </ul> <p>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.</p> <p>Other alternative I have seen is Infinispan, but it does not expose entry-level statistics - only cache-level statistics - and requires JMX.</p>
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    1. COhttp://memcached.org/
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    2. COWhat is the driver for having persistent storage of the cache? If the driver is to be able to have the cache available on restart, you could just write a function that runs on startup to repopulate the cache, taking the data from a separate, permanent store.
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    3. CO@robjohncox This is why: I need to cache reports, which are generated on demand. I need to limit to "X" the number of stored items. When "X" has been reached and a new report is requested I need to remove the "least-frequently-used" entry (LFU). When the reporting data changes in my data warehouse I need to know which ones are the "Y" most-frequently-used reports (Y < X), invalidate the cache, re-generate those reports, and re-cache them. All these are the typical operations of caching tools. I just need to avoid re-generating everything when my server restarts. Does this make more sense?
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