Saturday, December 12, 2009

not all promotions are "awarded" to long-surviving objects

GC commentators usually tiptoes around this tricky topic -- "generational GC typically promote an object from eden to old gen only when it has survived a few minor collections". It's not a hard guarantee that every promoted has survived at least 2 minor GC[1]

[1] but I believe there is a guarantee of at least 1 survival. Very simple, promotion can only happen during collection. If an object is promoted then it must be live at the time.

[[javaPerformance]] make it clear that premature promotion does happen -- a new object is promoted during its very first collection. This object (like all new objects) is likely to become garbage soon, but once promoted will not be examined until a major GC. This tends to litter the oldgen with garbage.

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