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