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[eclipselink-users] SoftCacheWeakIdentityMap sizing recommendation by the EclipseLink wiki documentation

Hello everyone,

 

I am trying to determine how to size our SoftCacheWeakIdentityMap per JPA mapped class. In reading the documentation on this subject (http://wiki.eclipse.org/Introduction_to_Cache_(ELUG)#Soft_Cache_Weak_Identity_Map_and_Hard_Cache_Weak_Identity_Map), it states “set this cache size to be as large as the maximum number of objects (of the same type) referenced within a transaction”. This seems like it could be an inappropriately low number for a web application where many users could be modifying different aggregate roots at all times of day.

 

Suppose we have a simple system of online ordering, and a simple JPA mapped domain model where Order instances are aggregate roots and Order has a one to many JPA mapped relationship to OrderLineItem (and of course the back pointing ManyToOne). If we expect a large number orders to be viewed, modified, or created per day, and we also in general expect the largest Order to have only 10 OrderLineItem instances, according to the statement above, we should set the SoftCacheWeakIdentityMap size to 10 for the OrderLineItem class. Lets say with this kind of Order volume, at peak periods some 100 Order instances are concurrently being viewed or modified. Would the recommendation in that environment be to set the SoftCacheWeakIdentityMap size for the OrderLineItem class to something more like 1000, assuming of course that you have adequate heap space to keep 1000+ OrderLineItem instances on the heap at any point in time?

 

I also saw the QueryMonitor and PerformanceProfiler, both in the org.eclipse.persistence.tools.profiler package mentioned to help understand the shared cache hit and miss information as noted here : http://dev.eclipse.org/mhonarc/lists/eclipselink-users/msg01744.html. Is either of those tools the best known approach for determining how good your identity map sizing choices are working?

 

Thanks,

 

Doug Gschwind






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