I want to understand the difference between:
-XX:+PrintGC and -verbose:gc
Apparently these look similar.
This article doesn't list the verbose:gc
http://www.oracle.com/technetwork/articles/java/vmoptions-jsp-140102.html
I also saw these two questions: How to redirect verbose garbage collection output to a file? and https://stackoverflow.com/a/1818039/2266682
but couldn't get much understanding.
In JDK 8 -verbose:gc is an exact alias for -XX:+PrintGC.
However, -verbose:gc is a standard option, while -XX:+PrintGC is not.
-XX:+PrintGC is deprecated since JDK 9 in favor of unified logging option -Xlog:gc, see JEP 158.
-verbose:gc still works in JDK 9 and 10.
Related
I have been using the following flags in my application using Java 8:-
1) PrintFLSStatistics=1
2) +PrintPromotionFailure
3) -XX:+PrintGCDateStamps
4) -XX:+PrintGCDetails
I have been moving the application to use Java 11 instead of Java 8. It seems these flags are either deprecated or not supported in Java 11. Please tell the alternatives of these flags in Java 11.
Thanks for your time,
In Java 11, you have to use -Xlog instead. For example: java -Xlog:gc\*::time -jar my.jar will log something like
[2020-02-19T18:32:50.107-0300] Heap region size: 1M
[2020-02-19T18:32:50.119-0300] Using G1
[2020-02-19T18:32:50.119-0300] Heap address: 0x000000070a200000, size: 3934 MB, Compressed Oops mode: Zero based, Oop shift amount: 3
-Xlog is the general logging configuration option for logging in the HotSpot JVM. It's a tag-based system where gc is one of the tags. To
get more information about what a GC is doing, you can configure
logging to print any message that has the gc tag and any other tag.
The command line option for this is -Xlog:gc*.
See:
https://docs.oracle.com/javase/9/tools/java.htm#GUID-BE93ABDC-999C-4CB5-A88B-1994AAAC74D5
https://docs.oracle.com/en/java/javase/11/gctuning/garbage-collector-implementation.html#GUID-A24775AB-16A3-4B86-9963-76E5AC398A3E
On 64 bit linux, with java8, when running java command, it seems all the 3 options -client / -server / -d64 are using the 64-bit server compiler.
The questions are: (for 64bit linux with java8)
Since -client and -server use the same compiler, does it makes any difference to specify one of the 2 options?
For a long running java daemon program, is it preferred to use -server together with -XX:+TieredCompilation or without it, when during the startup time it's ok to be a little slow.
Look at the file jre/lib/amd64/jvm.cfg. You'll likely see the lines
-server KNOWN
-client IGNORE
This means that -client option is ignored. -server also does nothing, since JDK 8 for x64 has only one JVM that includes both C1 and C2 compilers, and the tiered compilation is on by default.
with -XX:+TieredCompilation or without it
Does not matter, because this option is on by default. The advanced compilation policy works fine for both client-grade and server-grade applications. There is no usually need to turn it off manually.
I am trying GC log rotation in JDK 8.So I have achieved it by using below GC Log JVM parameter
-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xloggc:verbose-jdk8-gc.log -XX:+PrintGCDateStamps
-XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=5 -XX:GCLogFileSize=1k
But Now I want that This should also compressed when Rotation is done.
So is there any JVM Parameter in JDK 8 for compression of GC Log ?
Is there any one who can help me.
On Linux, you can use logroate: https://linux.die.net/man/8/logrotate to manage the rotation and compression of JVM gc log.
I am facing a strange issue while instrumenting java web application using ASM 5.0.3 / Java 1.7_80 / Apache Tomcat-6.0.35.
After server started with in 1 or 2 days code cache memory is completely filled 100% and never Garbage collected. Same is verified without Instrumentation which is working fine & code cache never fills 100%
I am using "JSRInlinerAdapter" in my instrumentation code. Since my application contains all class file versions from 48 to 51 (1.4 to 1.7)
My question is - Is code cache memory filled with inline methods when JIT compiler compiles these methods? (since i use JSRInlinerAdapter) ?
Additional info
I am using following VM arguments
-Djava.util.Arrays.useLegacyMergeSort=true
-XX:+UseCodeCacheFlushing
-Djsse.enableCBCProtection=false
-XX:NewSize=384m
-XX:MaxNewSize=384m
-XX:PermSize=384m
-XX:MaxPermSize=384m
-XX:+DisableExplicitGC
-XX:MaxGCPauseMillis=400
-XX:MaxGCMinorPauseMillis=100
-XX:+UseG1GC
-XX:+UnlockDiagnosticVMOptions
-XX:+G1SummarizeConcMark
-XX:+UseTLAB -XX:NewRatio=3
-XX:+UseCMSInitiatingOccupancyOnly
-XX:InitiatingHeapOccupancyPercent=30
-XX:ConcGCThreads=5
-XX:ParallelGCThreads=20
-XX:+UseFastAccessorMethods
-XX:+UseAdaptiveGCBoundary
-XX:+UseStringCache
-XX:+AggressiveOpts
-Xms1536m
-Xmx1536m
What could be the reason to fill code cache quickly?
What is the best way howto monitor usage of Eden and Survivor heap spaces?
I have all the GC logging options on but I can see only YoungGen occupation:
-XX:+PrintTenuringDistribution -XX:+UnlockDiagnosticVMOptions -XX:+LogVMOutput -XX:LogFile=jvm.log -server -XX:+HeapDumpOnOutOfMemoryError -XX:+DisableExplicitGC -Xloggc:gc.log -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -showversion -XX:+PrintClassHistogramBeforeFullGC -XX:+PrintClassHistogramAfterFullGC -XX:+UseParallelOldGC -XX:ParallelGCThreads=4 -XX:MaxTenuringThreshold=15
I would use VisualGC but cannot find its distribution anywhere. The default distribution of VisualVM that comes with JDK does not come with VisualGC. The VisualGC plugin links to the VisualGC site are broken.
UPDATE: jstat is what I was looking for, specifically :
jstat -gcutil -t <pid> <interval> <number_of_samples>
Depending on what you mean by "monitor", you might just need jstat. Check out the -gc* options.
If I understand you correctly, I think you can use JVisualVM to monitor your Java applications.
According to this page, you can download the relevant plugin center "updates.xml" file, an install it per the instructions. Then you can install the VisualGC plugin.
But the page also says that you should simply be able to install plugins using "Tools | Plugins | Available Plugins".
The links to projects on java.net are often broken in my experience. You typically have to look harder to find stuff that is hosted there.