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Note that objects in the younger generation that persist for longer durations are _tenured_ and are moved to the _tenured generation_. Few younger generation objects continue to live through to the next garbage collection cycle. The rest become ready to be collected in the impending collection cycle \[[Oracle 2010a|AA. Bibliography#Oracle 10a10]\].

With generational GCs, use of short-lived immutable objects is generally more efficient than use of long-lived mutable objects, such as object pools. Avoiding object pools improves the garbage collector's efficiency. Object pools bring additional costs and risks: they can create synchronization problems and can require explicit management of deallocations, possibly creating problems with dangling pointers. Further, determining the correct amount of memory to reserve for an object pool can be difficult, especially for mission-critical code. Use of long-lived mutable objects remains appropriate in cases where allocation of objects is particularly expensive (for example, when performing multiple joins across databases). Similarly, object pools are an appropriate design choice when the objects represent scarce resources, such as thread pools and database connections.

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