I read this article "Use Lucene's MMapDirectory on 64bit platforms, please!" and it said the MMapDirectory is better than other Directory because it will void copy data between file system cache and java heap. I checked the source code of NIOFSDirectory, and in new Buffer method it called "ByteBuffer.wrap(newBuffer)", the generated ByteBuffer is HeapByteBuffer. And it will indeed copy data between file system cache and java heap. Why not use ByteBuffer.allocateDirect to generate DirectyByteBuffer, and it will store data directly in file sysytem cache, not java heap. If in this case , what is the different in performance between NIO and MMap? Or allocate directy memory in still slower than Mmap? Maybe I made some misunderstanding of lucene code, thank you for any suggestion in advance.
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