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0 pointschrisseaton7y ago0 comments

> I expect this needs to be taken with a chunk of salt, since a smaller heap can only require so much GC...

Pause times. Not GC times. Shenandoah pauses to scan the root set only. The size of the root set doesn't grow with the size of the heap.

You can have a large root set and a tiny heap, or a tiny root set and a massive heap. They're entirely independent.

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mehrdadn7y ago

What happens if a huge object becomes unreferenced and a new one of the same size is then allocated before the older one is GC'd (and you don't have enough memory to hold both simultaneously)? Does it just crash or does it pause to collect the older objects first?

brianpgordon7y ago

It won't crash, but what it does is somewhat complicated. There's a section in the OpenJDK wiki addressing this question:

https://wiki.openjdk.java.net/display/shenandoah/Main#Main-F...

mehrdadn7y ago

> Full GC. If nothing helped, for example, when Degenerated GC had not freed up enough memory, Full GC cycle would happen, and compact the heap to the max. Certain scenarios, like the unusually fragmented heap coupled with implementation performance bugs and overlooks, would be fixed only by Full GC. This last-ditch GC guarantees that application would not fail with OOM, if there is at least some memory is available.

> Usual latency induced: >100 ms, but can be more, especially on a very occupied heap

Seems like it confirms precisely what I wrote? You can get longer pauses the less memory you have left, i.e. the more of the heap you've used...

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0 pointschrisseaton7y ago0 comments

> I expect this needs to be taken with a chunk of salt, since a smaller heap can only require so much GC...

Pause times. Not GC times. Shenandoah pauses to scan the root set only. The size of the root set doesn't grow with the size of the heap.

You can have a large root set and a tiny heap, or a tiny root set and a massive heap. They're entirely independent.

0 comments

mehrdadn7y ago

brianpgordon7y ago

It won't crash, but what it does is somewhat complicated. There's a section in the OpenJDK wiki addressing this question:

https://wiki.openjdk.java.net/display/shenandoah/Main#Main-F...

mehrdadn7y ago

> Usual latency induced: >100 ms, but can be more, especially on a very occupied heap

Seems like it confirms precisely what I wrote? You can get longer pauses the less memory you have left, i.e. the more of the heap you've used...

1 more reply

j / k navigate · click thread line to collapse