출처 : http://jyates.github.io/2012/11/05/rolling-java-gc-logs.html
If you are running a java process, you probably want to keep track of what the garbage collector is doing. You can access this via jconsole or by logging the gc actions by adding:
-Xloggc:gc.log -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStampswhich logs to the ‘gc.log’ file.
And for simple cases, that will probably work just fine…until your process starts running row more than a few days. The GC log is not rolled automatically, potentially resulting in a log that can easily grow out of control and fill up your filesystem.
Bad news bears!
What you really want to do roll the logs periodically. You could do this manually with a cron job (which means you might missing some elements), or every time you restart the process (but if you don’t restart often, you’re up a creek) or send the log to your own custom logger (which is can be tricky to get right).
All pretty ugly solutions. I sure wish we had something better…
As of Oracle Java 1.6_34 (or 1.7_2 in the latest minor version), we do! GC logs can be automatically rolled at a certain size and retain only a certain number of logs.
To turn on simple log rolling, you only need to add (in addition neccessay gc log arguments mentioned above) to your java command line options:
-XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=<number of files> -XX:GCLogFileSize=<size>where <number of files> is just an integer and <size> is the size of the file (e.g 16K is 16 kilobytes, 128M is 128 megabytes, etc.). Rolled files are appened with .<number>, where earlier numbered files are the older files.
Suppose you ran an java program with the parameters:
$ java -Xloggc:gc.log -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStamps -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=5 -XX:GCLogFileSize=128Kyou might see something like the following show up in your directory:
-rw-r--r-- 1 jyates staff 90K Nov 5 18:25:39 2012 gc.log.0
-rw-r--r-- 1 jyates staff 128K Nov 5 18:25:25 2012 gc.log.1
-rw-r--r-- 1 jyates staff 128K Nov 5 18:25:29 2012 gc.log.2
-rw-r--r-- 1 jyates staff 128K Nov 5 18:25:33 2012 gc.log.3
-rw-r--r-- 1 jyates staff 128K Nov 5 18:25:36 2012 gc.log.4What’s really nice note here is that GC logs beyond the specified number areautomatically deleted, ensuring that you know exactly (+/- a few kilobytes for the occasional heavy load) how many log files you will have.
Pretty cool!
Unfortunately, if you attempt to turn on log rolling and forget to include the number of files or the size, the jvm will not turn on logging and instead tell you:
To enable GC log rotation, use -Xloggc:<filename> -XX:+UseGCLogRotaion -XX:NumberOfGCLogFiles=<num_of_files> -XX:GCLogFileSize=<num_of_size>
where num_of_file > 0 and num_of_size > 0
GC log rotation is turned offthis is wrong!
Double check your other parameters, and try again; you definitely want to use -XX:+UseGCLogFileRotation.
Hopefully this helps you setup your own log rolling. If you have any other JVM/GC tricks, I’d love to hear about them.
Notes:
- This is actually a best effort rolling process. If you are doing a lot GC work (e.g. leaning on the ‘garbage collect’ button in jconsole), the log may grow larger. However, as soon as the jvm has a chance it will then roll the log.
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출처 : https://confluence.atlassian.com/display/CONFKB/Enable+Garbage+Collection+Logging
Enable Garbage Collection Logging
Why Garbage Colllection Logging?
Garbage Collection logs are useful when trying to isolate issues within Java based applications as they will pinpoint blocked, hung or stuck threads that may be causing downstream effects in the application. It is always useful to collect at least 10 minutes of garbage collection logs, but analysis accuracy is often increased by the amount of recent log data to review.
For Linux
Add the following parameters into your Confluence System Properties, in setenv.sh (be sure to enter the path for your <confluence-home> directory)
The parameter -XX:+PrintGCCause was introduced within Java 1.7.0_45 and will not work if you are using a version of Java prior to that version. Please check the version of Java that is being used by your instance of Confluence prior to using this flag.
For Windows
Batch file
If you start Confluence using 'start-confluence.bat', add the below code to setenv.bat
NB: This will create the GC logs in the <confluence-install> directory.
Service
If you start Windows as a service, add the below to the service by following these steps (be sure to enter the path for your <confluence-home> directory)
NB: There is no way to include the DATE and TIME variables in the filename when starting as a Windows Service. This means the gc.log file will be overwritten on each startup. If you need to analyse the file, be sure to copy it before restarting the service.