Benju Benju - 1 month ago 24
Java Question

Java G1 garbage collection in production

Since Java 7 is going to use the new G1 garbage collection by default is Java going to be able to handle an order of magnitude larger heap without supposed "devastating" GC pause times? Has anybody actually implemented G1 in production, what were your experiences?

To be fair the only time I have seen really long GC pauses is on very large heaps, much more than a workstation would have. To clarify my question; will G1 open the gateway to heaps in the hundreds of GB? TB?

Answer

It sounds like the point of G1 is to have smaller pause times, even to the point where it has the ability to specify a maximum pause time target.

Garbage collection isn't just a simple "Hey, it's full, let's move everything at once and start over" deal any more--it's fantastically complex, multi-level, background threaded system. It can do much of its maintenance in the background with no pauses at all, and it also uses knowledge of the system's expected patterns at runtime to help--like assuming most objects die right after being created, etc.

I would say GC pause times are going to continue to improve, not worsen, with future releases.

EDIT:

in re-reading it occurred to me that I use Java daily--Eclipse, Azureus, and the apps I develop, and it's been a LONG TIME since I saw a pause. Not a significant pause, but I mean any pause at all.

I've seen pauses when I right-click on windows explorer or (occasionally) when I hook up certain USB hardware, but with Java---none at all.

Is GC still an issue with anyone?