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    <title>
      miscellaneous
    </title>

## Misc Tools

The misc package has various tools for splitting/merging indices,
changing norms, finding high freq terms, and others.

## NativeUnixDirectory

**NOTE**: This uses C++ sources (accessible via JNI), which you'll
have to compile on your platform.

[](xref:Lucene.Net.Store.NativeUnixDirectory) is a Directory implementation that bypasses the
OS's buffer cache (using direct IO) for any IndexInput and IndexOutput
used during merging of segments larger than a specified size (default
10 MB).  This avoids evicting hot pages that are still in-use for
searching, keeping search more responsive while large merges run.

See [this blog post](http://blog.mikemccandless.com/2010/06/lucene-and-fadvisemadvise.html)
for details.

Steps to build:

*   <tt>cd lucene/misc/</tt>

   To compile NativePosixUtil.cpp -> libNativePosixUtil.so, run<tt> ant build-native-unix</tt>.

  <tt>libNativePosixUtil.so</tt> will be located in the <tt>lucene/build/native/</tt> folder

   Make sure libNativePosixUtil.so is on your LD_LIBRARY_PATH so java can find it (something like <tt>export LD_LIBRARY_PATH=/path/to/dir:$LD_LIBRARY_PATH</tt>, where /path/to/dir contains libNativePosixUtil.so)

   <tt>ant jar</tt> to compile the java source and put that JAR on your CLASSPATH

NativePosixUtil.cpp/java also expose access to the posix_madvise,
madvise, posix_fadvise functions, which are somewhat more cross
platform than O_DIRECT, however, in testing (see above link), these
APIs did not seem to help prevent buffer cache eviction.