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From "Koji Sekiguchi" <>
Subject What is MMapDirectory?
Date Sun, 09 Oct 2005 12:12:34 GMT

What is MMapDirectory?

I've searched mailing list archive, but cannot find it.
I could find the following explanation at Lucene 1.9 CHANGES.txt:

 8. Add MMapDirectory, which uses nio to mmap input files.  This is
    still somewhat slower than FSDirectory.  However it uses less
    memory per query term, since a new buffer is not allocated per
    term, which may help applications which use, e.g., wildcard
    queries.  It may also someday be faster. (cutting & Paul Elschot)

And I saw bug 31508:

[PATCH] MMapDirectory for huge index files

But I'm curious to know about MMapDirecotry in more detail about
the following point:

1. Were there any troubles in FSDirectory with huge index files?
2. Is MMapDirectory used for only searching? (not indexing?)
3. Why is MMapDirectory somewhat slower than FSDirectory?
4. Why does MMapDirectory use less memory while using mapped file (mmap)?

Thank you very much in advance,


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