Java Garbage Collection Logging: Difference between revisions
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Revision as of 03:27, 13 February 2017
Internal
Command Line Options
Java 8
Overview
In Java 8, GC logging is enabled with the -Xloggc:<file> (see below). The actual -XX values the JVM operates with are displayed at the top of the log file:
... CommandLine flags: -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=4294967296 -XX:+PrintGC -XX:+PrintGCTimeStamps -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseParallelGC ...
Options
-Xloggc:
-Xloggc:<file>
where <file> can be absolute or relative. In case of a relative path, it is relative to the current directory.
-XX:+PrintGC
-XX:+PrintGC
Enables printing of messages at every GC. By default, this option is disabled, but -Xloggc:<file> turns it on implicitly.
-XX:+PrintGCTimeStamps
-XX:+PrintGCTimeStamps
Enables printing of time stamps (time in seconds since the JVM started) at every GC. By default, this option is disabled. It is implicit turned on if -Xloggc:<file> is used. Time stamps recorded this way provide a chronology relative to the time the JVM started, but additional calculation is needed to translate the timestamps to normal timestamps, and it is only possible if the JVM start time is also recorded. A better way to record timestamps is to use [[]].
When used, the timestamps are recorded in the following format:
2017-02-12T19:26:03.328+0800:
-XX:+PrintGCDateStamps
-XX:+PrintGCDateStamps
-verbose:gc
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-XX:+UseGCLogFileRotation
-XX:NumberOfGCLogFiles=5
-XX:GCLogFileSize=3M