g1gc

问题 After reading some answers like this and JEP-346, I have realised that the G1 does release memory back to the OS. However does it release memory back to the OS, even to the point that current memory use can drop below the initial heap memory (i.e before this JEP, in my case JDK11)? Assume I have a Java 11 VM running with Xms and Xmx set as 5GB , on a 8GB RAM, however I am consuming only around 1GB . Will G1 release enough memory back to the OS? I didn't find any documentation anywhere which

问题 Recently I have tried to use G1GC from jdk1.7.0-17 in my java processor which is processing a lot of similar messages received from an MQ (about 15-20 req/sec). Every message is processed in the separate thread (about 100 threads in stable state) that serviced by Java limited thread pool. Surprisingly, I detected the strange behaviour - as soon as GC starts the full gc cycle it begins to use significant processing time (up to 100% CPU and even more). I was doing refactoring of the code

问题 Recently I have tried to use G1GC from jdk1.7.0-17 in my java processor which is processing a lot of similar messages received from an MQ (about 15-20 req/sec). Every message is processed in the separate thread (about 100 threads in stable state) that serviced by Java limited thread pool. Surprisingly, I detected the strange behaviour - as soon as GC starts the full gc cycle it begins to use significant processing time (up to 100% CPU and even more). I was doing refactoring of the code

问题 With j7u5, G1GC "-Xms3200m -Xmx3200m -XX:+UseG1GC -XX:ParallelGCThreads=14 -XX:ConcGCThreads=4 -XX:MaxGCPauseMillis=40 -XX:NewRatio=2 -XX:SurvivorRatio=10 -XX:+PrintGC -XX:+PrintGCDateStamps" for a given performance test, my application hits a long pause after 5-hour run predictably. Except this big one (and only), there are small initial-mark phases. Any suggestions to figure out what is happening to this long pause and how to tune it to avoid such a long pause which affects the latency

问题 Garbage First (G1) garbage collector http://weblogs.java.net/blog/opinali/archive/2009/02/here_comes_jdk.html Do you think this garbage collector is better for JRun, running ColdFusion 8? 回答1: I will tell you that updating the JVM in ColdFusion is a breeze, so I always update to the latest JVM once it's been released for a month. I haven't had any problems with any of the releases thus far and ColdFusion seems to be getting a little quicker with each update. That said, you should always

问题 I can't find any options relating to how G1 operates. The below two commands no longer work with java7. -XX:+G1ParallelRSetUpdatingEnabled -XX:+G1ParallelRSetScanningEnabled 回答1: Only options I am aware of that have an impact on G1 are: to activate: -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC to set the max GC pause time goal in milliseconds that G1 will attempt to meet: -XX:MaxGCPauseMillis=<X> to set the time interval over which GC pauses totaling up to MaxGCPauseMillis may take place:

问题 In Java 6 we used to use the following GC configuration to prevent Perm Gen OutOfMemoryException after several redeployments of our app: -XX:+UseConcMarkSweepGC -XX:+CMSClassUnloadingEnabled We're moving to Java 7 and want to use the new G1 GC, which from what I've read, moves the classes from the PermGen in Java memory to native memory. Is there some flag to enable unloading unused classes? 回答1: The G1 performs the class unloading during a Full GC, so you do not need to specify any

问题 I have been experimenting with G1GC with Java 8 (Oracle JVM) on one of my projects. My GC flags are effectively: -Xms64m -Xmx1024m -XX:+UseG1GC -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -Xloggc:/tmp/gc.log -XX:+PrintAdaptiveSizePolicy I observe that the heap grows much larger than the amount of live data I have. The GC logs show what I think is the root cause: [G1Ergonomics (Heap Sizing) attempt heap expansion, reason: recent GC overhead higher than threshold after GC, recent GC overhead: 10

问题 I am running a Java program with the G1 garbage collector using the following options: -XX:-UseBiasedLocking -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -verbose:gc -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -Xloggc:/var/tmp/gclog.out The output looks like this... 44900.297: [GC pause (young)44900.386 (initial-mark), 0.08894851 secs] : [GC concurrent-mark-start] [Parallel Time: 83.7 ms] [GC Worker Start Time (ms): 44900297.6 44900297.6 44900297.6 44900297.6 44900297.6 44900297.7 44900297.7

问题 I'm using the G1 garbage collector. You can enable adaptive size policy logs with -XX:+PrintAdaptiveSizePolicy Here's sample output in the GC logs 1822.780: [G1Ergonomics (Heap Sizing) attempt heap expansion, reason: recent GC overhead higher than threshold after GC, recent GC overhead: 11.48 %, threshold: 10.00 %, uncommitted: 0 bytes, calculated expansion amount: 0 bytes (20.00 %)] Which JVM flag manages the threshold: 10.00 % that is mentioned in there? Below are some of the flags that