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https://issues.apache.org/jira/browse/LUCENE-3178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13094740#comment-13094740
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Robert Muir commented on LUCENE-3178:
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It might even be worth doing the mmap from NativePosixUtil, dealing with all
the round-to-pagesize etc that you need, and accessing it with sun.misc.Unsafe.
I did a little prototype a while back that stole the address from
MappedByteBuffer and used Unsafe for all ops with no bounds checks, and the
performance improvements were pretty interesting :) But the problem with that
approach is you still can't FileChannel.map a file > Integer.MAX_VALUE, meaning
we have to handle all the stupidity of multiple mappings, but I think with a
native mmap call you could just map the whole thing and avoid this hassle...
> Native MMapDir
> --------------
>
> Key: LUCENE-3178
> URL: https://issues.apache.org/jira/browse/LUCENE-3178
> Project: Lucene - Java
> Issue Type: Improvement
> Components: core/store
> Reporter: Michael McCandless
>
> Spinoff from LUCENE-2793.
> Just like we will create native Dir impl (UnixDirectory) to pass the right OS
> level IO flags depending on the IOContext, we could in theory do something
> similar with MMapDir.
> The problem is MMap is apparently quite hairy... and to pass the flags the
> native code would need to invoke mmap (I think?), unlike UnixDir where the
> code "only" has to open the file handle.
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