Hi, On Mon, 2018-05-14 at 13:22 -0600, Shawn Heisey wrote: > On 5/14/2018 11:41 AM, Thomas Schatzl wrote: > > There is unfortunately no way to get detailed information in a > > product build about what Hotspot thinks.
To clarify that statement a bit: you need to enable -XX:+Verbose to get exact information on what Hotspot thinks, but Verbose can only be changed in debug builds. In JDK9+ you could use -Xlog:gc+ergo=trace to get this information.. > > However not only gc overhead is accounted for in the decision to > > give an OOME, but also how much memory the full gcs free. > > > > Probably the most important flag here would be GCHeapFreeLimit: > > simplified, if free space after full gc is below this percentage of > > total heap, that full gc does not count against GCOverHeadLimit. > > > > Looking at the log output, after Full GC there is ~4% of max heap > > available. The default value for GCOverHeadLimit is 2 (percent). > > I have a question sparked by this discussion, but it's only > indirectly related. > > How long a timeframe is examined to determine whether the 98% and 2% > thresholds are violated? This information is not in the > documentation that I've been able to find. Here's an example of a > java 8 documentation link where that information is not shown: > > https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/cm > s.html#sthref35 I did not think this is actually documented - I had to look at the code :) There is a flag called AdaptiveSizePolicyGCTimeLimitThreshold (default: 5) which defines the amount of consecutive GCs that need to exceed these thresholds to result in an OOME. That counter is reset at the first GC not exceeding the thresholds. I hope this was what you were asking for. Thanks, Thomas _______________________________________________ hotspot-gc-use mailing list hotspot-gc-use@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
