Parallel Collector GC Log Message Format

JVM Tutorials - Herong's Tutorial Examples - Version 4.23, by Dr. Herong Yang

JVM Tutorials - Herong's Tutorial Examples

∟Memory Management and Garbage Collectors

∟Parallel Collector GC Log Message Format

This section provides examples of HotSpot Parallel Collector GC log messages.

Different garbage collectors also generate different log messages. Here is an example of log messages generated by the Parallel Collector:

C:\>\progra~1\java\jdk1.8.0\bin\java -Xms2m -Xmx64m -XX:+UseParallelGC
   -XX:+PrintGCDetails GarbageCollection

Step/TotalMemory/FreeMemory/UsedMemory:
   [GC (Allocation Failure) 
      [PSYoungGen: 450K->248K(768K)] 
      1218K->1104K(1792K), 
      0.0035187 secs] 
   [Times: user=0.00 sys=0.00, real=0.00 secs] 
   -- Minor GC. 
      PSYoungGen stands for Parallel Scavenge Young Generation

1   1835008   472000   1363008

   [GC (Allocation Failure) 
      [PSYoungGen: 731K->240K(768K)] 
      2099K->2068K(2816K), 
      0.0039119 secs] 
   [Times: user=0.00 sys=0.00, real=0.00 secs] 

   [Full GC (Ergonomics) 
      [PSYoungGen: 240K->0K(768K)] 
      [ParOldGen: 1828K->2037K(3840K)] 
      2068K->2037K(4608K), 
      [Metaspace: 44K->44K(4480K)], 
      0.0642066 secs] 
   [Times: user=0.05 sys=0.00, real=0.07 secs] 
   -- Full GC.
      ParOldGen stands for Parallel Old Generation

2   4718592   2347656   2370936

...

Heap
 PSYoungGen      total 14592K, used 2379K [0x068c0000, 0x07e00000...
  eden space 7424K, 32% used [0x068c0000,0x06b12eb0,0x07000000)
  from space 7168K, 0% used [0x07700000,0x07700000,0x07e00000)
  to   space 7168K, 0% used [0x07000000,0x07000000,0x07700000)
 ParOldGen       total 43776K, used 32474K [0x03e00000, 0x068c000...
  object space 43776K, 74% used [0x03e00000,0x05db6a80,0x068c0000)
 Metaspace used 45K, capacity 2242K, committed 2368K, reserved 4480K

As you can see, the Parallel Collector log message format is identical to the Serial Collector, except that different GC algorithms are used on Young Generation and on Tenured (Old) Generation.

The Parallel Collector does not include timestamps in the log messages. So you have to add it by using "–XX:+PrintGCTimeStamps" option.

Last update: 2014.

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