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IBM WebSphere - Full GC (garbage collection)

Updated:   |  IBM WebSphere articles

Full GC stands for Full Garbage Collection. Full GC occurs when an application servers heap space is full, and the application servers garbage collector removes unneeded objects from the heap space. When this occurs, a Full GC event appears in the application servers log. 

2017-09-12T08:55:35.596-0500: 187646.780: 
[Full GC (Allocation Failure) 2017-09-12T08:55:35.596-0500: 187646.780: 
[Tenured: 64K->64K(64K), 1.2320452 secs] 471871K->352446K(471872K), 
[Metaspace: 391525K->391525K(1359872K)], 1.2325193 secs] 
[Times: user=1.02 sys=0.00, real=1.23 secs]


Responding to Full GC alerts

  • Check the application servers logs for Out of Memory events. If there are Out of Memory events in the logs, refer to the Out of Memory article.
  • Determine if heap size is too small for the application (large footprint)


Large footprint

An application server may have Full GC events if the number or size of the objects placed in the heap space by an application is excessive. For example, let's say an application server is configured with a heap size of 128 MB. If an application on the application server is placing PDFs that are 50 KB each in the heap space, it will not take long for the heap space to be used.

When the number or size of objects placed in the heap space is excessive, there are a couple options. One option is to increase the heap space of the application server, so that the heap space can handle more objects. Another option is to see if a change can be made to the application to reduce the number or size of the objects being placed in the heap space.


How to change the heap size

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