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From Andrei Alecu <>
Subject Lucene + Windows 2008 R2 performance issues
Date Thu, 18 Feb 2010 11:25:23 GMT
It seems like Microsoft changed the way the memory manager works in the 
new Windows 7 kernel (which is what Windows 2008 R2 uses), not letting 
the system cache grows to use up all available RAM any more. (at least 
not in a predictable manner)

Here's a reference:

    "The memory management algorithms were updated to address this
    problem in Windows 7 and Windows Server 2008 R2 operating systems.
    Therefore, we do not recommend that you use the provided functions
    or the Microsoft Windows Dynamic Cache Service in computers that are
    running Windows 7 or Windows Server 2008 R2."

This is in some circumstances a good thing, but it also means that 
things like Lucene now need to access the hard drive more than before. 
We're storing a lucene index on an iSCSI SAN, which used to work great 
pre W2K8 R2 because it eventually found its way into the system cache, 
and it wouldn't hit the network any more. This doesn't happen any more 
with R2 and we see some query time degradation.

The solution to this issue would be to use Memory Mapped I/O, but I see 
that MMapDirectory is not implemented, are there any plans to implement it?

There is first class support for Memory Mapped Files in .NET 4.0 which 
is still some time away, but until then the Win32 API could be used.

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