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README.JAVA.txt: explain the 'mca' parameter 'mpi_java_eager'

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This commit was SVN r31464.
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Oscar Vega-Gisbert 2014-04-20 14:35:03 +00:00
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README.JAVA.txt
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@ -192,6 +192,19 @@ practical point of view, this implies an overhead associated to all
buffers that are represented by Java arrays. The overhead is small
for small buffers but increases for large arrays.
There is a pool of temporary buffers with a default capacity of 64K.
If a temporary buffer of 64K or less is needed, then the buffer will
be obtained from the pool. But if the buffer is larger, then it will
be necessary to allocate the buffer and free it later.
The default capacity of pool buffers can be modified with an 'mca'
parameter:
mpirun --mca mpi_java_eager size ...
Where 'size' is the number of bytes, or kilobytes if it ends with 'k',
or megabytes if it ends with 'm'.
An alternative is to use "direct buffers" provided by standard
classes available in the Java SDK such as ByteBuffer. For convenience
we provide a few static methods "new[Type]Buffer" in the MPI class