"-XX:+PrintGCDateStamps" - Calendar Timestamp on GC Messages

Java GC Tutorials - Herong's Tutorial Examples - Version 1.01, by Dr. Herong Yang

Java GC Tutorials - Herong's Tutorial Examples

∟"-XX:+PrintGCDateStamps" - Calendar Timestamp on GC Messages

This section describes the garbage collection logging option, '-XX:+PrintGCDateStamps', which adds a calendar timestamp to each GC log message.

Now, let's try the "-XX:+PrintGCDateStamps" garbage collection logging option to see what we will get in the log file:

C:\>\progra~1\java\jdk1.8.0\bin\java -Xms2m -Xmx64m -XX:+PrintGCDetails 
   -XX:+PrintGCDateStamps -Xloggc:gc.log  GarbageCollection
   
Step/TotalMemory/FreeMemory/UsedMemory:
1   2031616   698848   1332768
2   3874816   1473392   2401424
3   3874816   425688   3449128
4   8970240   4442016   4528224
...
(Ctrl-C)

C:\>type gc.log
CommandLine flags: -XX:InitialHeapSize=2097152 -XX:MaxHeapSize=67108864
   -XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails 
   -XX:+PrintGCTimeStamps -XX:-UseLargePagesIndividualAllocation 
2018-04-01T21:00:47.418-0100: 0.719: [GC (Allocation Failure) 
   0.725: [DefNew: 889K->64K(960K), 0.0074037 secs] 
   889K->755K(1984K), 0.0131249 secs] 
2018-04-01T21:00:48.448-0100: 1.748: [GC (Allocation Failure) 
   1.748: [DefNew: 865K->64K(960K), 0.0059537 secs]
   1.754: [Tenured: 1476K->1540K(1540K), 0.0502278 secs] 
   1557K->1540K(2500K),...
2018-04-01T21:00:49.512-0100: 2.813: [GC (Allocation Failure) 
   2.813: [DefNew: 1061K->127K(1216K), 0.0049146 secs] 
   2601K->2580K(3784K), 0.0050707 secs] 
2018-04-01T21:00:50.527-0100: 3.827: [GC (Allocation Failure) 
   3.827: [DefNew: 1171K->127K(1216K), 0.0047282 secs]
   3.832: [Tenured: 3492K->3604K(3604K), 0.0049167 secs] 
   3624K->3620K(4820K),...
...
Heap
 def new generation   total 19648K, used 6651K [...
  eden space 17472K,  38% used [...
  from space 2176K,   0% used [...
  to   space 2176K,   0% used [...
 tenured generation   total 43712K, used 32990K [...
   the space 43712K,  75% used [...
 Metaspace used 1561K, capacity 2242K, committed 2368K, reserved 4480K

Notes on the output:

Three JVM options: "-XX:+PrintGC", "-XX:+PrintGCTimeStamps" and "-XX:-UseLargePagesIndividualAllocation" were added by default.
A true calendar timestamp was added for each log message. I will explain how to read log messages later when we have better understandings on how each garbage collector works.
A summary of the heap memory area usage was reported at the end.

Obviously, extra calendar timestamp generated from the "-XX:+PrintGCDateStamps" option does help if you want to troubleshoot any memory issues. So you should use "-XX:+PrintGCPrintGCDetails" all the time.

Last update: 2018.

Table of Contents

About This Book

Heap Memory Area and Size Control

►JVM Garbage Collection Logging

Garbage Collection Demo Program

Garbage Collection Logging Options

"-XX:+PrintGC" - GC Logging Option for Short Messages

"-XX:+PrintGCDetails" - Option for Detailed GC Messages

►"-XX:+PrintGCDateStamps" - Calendar Timestamp on GC Messages

"-XX:+PrintGCApplicationStoppedTime" - Application Pause Durations

"-XX:+PrintGCApplicationConcurrentTime" - Application Running Durations