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      miscellaneous
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<h2>Misc Tools</h2>

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

<a name="NativeUnixDirectory"></a>
<h2>NativeUnixDirectory</h2>

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

<p>
{@link org.apache.lucene.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.

<p>
See <a target=_top href="http://blog.mikemccandless.com/2010/06/lucene-and-fadvisemadvise.html">this blog post</a>
for details.

Steps to build:
<ul>
  <li> <tt>cd lucene/misc/</tt>

  <li> To compile NativePosixUtil.cpp -> libNativePosixUtil.so, run<tt> ant build-native-unix</tt>.
  
  <li><tt>libNativePosixUtil.so</tt> will be located in the <tt>lucene/build/native/</tt> folder

  <li> 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)

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

<p>
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.
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