Could you please explain this GC log message?

Question

2013-12-15T22:52:05.154-0500: 1.078: [Full GC (System) [PSYoungGen: 1600K->0K(27776K)] [PSOldGen: 0K->1502K(63360K)] 1600K->1502K(91136K) [PSPermGen: 9139K->9139K(65536K)], 0.0282750 secs] [Times: user=0.03 sys=0.00, real=0.03 secs]

Above is the log snippet from the log file. I got the log by adding the jvm parameter like below.

-Xloggc:/tmp/gc.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps

For now I want to know what's the meaning of

[PSOldGen: 0K->1502K(63360K)] 1600K->1502K(91136K)

How does it happen?

Answer 1

This log line indicates that a Full GC was invoked by calling System.gc().

1502K was promoted from YoungGen to OldGen. 1600K->1502K(91136K) indicates total Heap usage going from 1600K to 1502K, total heap size 91136K.

See Java Garbage Collection Log messages and How to read a verbose:GC output? for more details.