How to Enable Garbage Collection (GC) Logging
Platform notice: Server and Data Center only. This article only applies to Atlassian products on the server and data center platforms.
Platform notice: Server and Data Center only. This article only applies to Atlassian products on the server and data center platforms.
Purpose
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.
Solution
For Linux
Add the following parameters into your Confluence System Properties, in the <confluence-install>/bin/setenv.sh file (be sure to enter the path for your <confluence-home> directory)
-Xloggc:<confluence-home>/logs/`date +%F_%H-%M-%S`-gc.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintTenuringDistribution -XX:+PrintGCCause
-XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=10 -XX:GCLogFileSize=5MThe 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
rem Create a timestamp with date and time, replacing ' ' with '0' and '/' with '-'
set atlassian_timestamp=%DATE:~-4%.%DATE:~4,2%.%DATE:~7,2%_%TIME:~0,2%.%TIME:~3,2%.%TIME:~6,2%
set atlassian_timestamp=%atlassian_timestamp: =0%
set atlassian_timestamp=%atlassian_timestamp:/=-%
set atlassian_logsdir=%~dp0..\logs
set CATALINA_OPTS=%CATALINA_OPTS% -Xloggc:"%atlassian_logsdir%\gc-%atlassian_timestamp%.log"
set CATALINA_OPTS=%CATALINA_OPTS% -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=10 -XX:GCLogFileSize=5M -XX:+PrintGCCause
set CATALINA_OPTS=%CATALINA_OPTS% -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintTenuringDistribution NB: This will create the garbage collection 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)
-Xloggc:<confluence-home>\logs\gc-%t.log
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-XX:+PrintGCTimeStamps
-XX:+PrintGCCause
-XX:+PrintTenuringDistribution
-XX:+UseGCLogFileRotation
-XX:NumberOfGCLogFiles=10
-XX:GCLogFileSize=5MNote - When using Java 11
In Java 11 some JVM flags including those used in Java 8 for Garbage Collection Logging have been removed.
If these are still contained in the JVM flags specified in the setenv.sh or setenv.bat the JVM will not be able to start.
It's known that the following options are unrecognized in Java 11:
- -d64
- PrintGCTimeStamps
- PrintGCDateStamps
- PrintTenuringDistribution
- PrintGCCause
- PrintGCDetails
- UseGCLogFileRotation
- NumberOfGCLogFiles
- GCLogFileSize
In Java 11, these GCLog options are now handled by Xlog, there is a conversion table below:
Please refer to the Knowledge Article below in case JVM is not able to start and Error Unrecognized VM option 'UseGCLogFileRotation' is seen