The default behavior for DirectByteBuffer is that 64 MB of memory is reserved at startup for direct byte buffers. The buffers are then allocated out of the reserved space. If a request for a buffer is made, and there is not sufficient space to satisfy the allocation, then a call to system.gc is made in order to free up any buffers that are no longer in use. If, after the system gc, there is still insufficient memory to satisfy the allocation, then the reserved space is expanded by 32Mb.

 

This behavior can be overridden with the -XX:MaxDirectMemorySize command line option. This option will set the amount of reserved space for direct byte buffers to the supplied value. This will eliminate the calls to system.gc until the space gets close to being filled. Note however that when this option is used, the reserved space cannot be increased as the value specified is taken to be the maximum allowable. Once the space fills and system gc cannot free up enough space, then an OutOfMemoryError will occur.

 

Related Content:

• Tracing application use of direct byte buffers
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• Setting the WebSphere Application Server WebContainer to synchronous mode

 

 

 

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Tags:  nativememory websphere was directbytebuffer oom disableexplicitgc noom system.gc websphere_application_ser...