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From Cheng <zhoucheng2...@gmail.com>
Subject Re: RAMDirectory unexpectedly slows
Date Sat, 16 Jun 2012 11:18:21 GMT
After a number of test, the performance of MMapDirectory is not even close
to that of RAMDirectory, in terms of speed.

My application w/ the former can only deal with 10 tasks per round while it
could handle over 90 w/ RAMDirectory.

I use the application in Linux.

What can be the reasons?

Thanks.


On Tue, Jun 5, 2012 at 7:53 AM, Uwe Schindler <uwe@thetaphi.de> wrote:

> This is managed by your operating system. In general OS kernels like Linux
> or Windows use all free memory to cache disk accesses.
>
> -----
> Uwe Schindler
> H.-H.-Meier-Allee 63, D-28213 Bremen
> http://www.thetaphi.de
> eMail: uwe@thetaphi.de
>
>
> > -----Original Message-----
> > From: Cheng [mailto:zhoucheng2008@gmail.com]
> > Sent: Monday, June 04, 2012 6:10 PM
> > To: java-user@lucene.apache.org
> > Subject: Re: RAMDirectory unexpectedly slows
> >
> > Can I control the size of ram given to either MMapDirectory or
> > ByteBufferDirectory?
> >
> > On Mon, Jun 4, 2012 at 11:42 PM, Uwe Schindler <uwe@thetaphi.de> wrote:
> >
> > > Hi,
> > >
> > > If you are using MMapDirectory or this ByteBufferDirectory (which is
> > > similar to the first) the used RAM is outside JVM heap, it is in the
> > > FS cache of the OS kernel. Giving too much memory to the JVM penalizes
> > > the OS cache, so give only as much as the App needs. Lucene and the OS
> > > kernel will then utilize the remaining memory for caching.
> > >
> > > Please read docs of MMapDirectory and inform yourself about mmap in
> e.g.
> > > Wikipedia.
> > >
> > > Uwe
> > > --
> > > Uwe Schindler
> > > H.-H.-Meier-Allee 63, 28213 Bremen
> > > http://www.thetaphi.de
> > >
> > >
> > >
> > > Cheng <zhoucheng2008@gmail.com> schrieb:
> > >
> > > Please shed more insight into the difference between JVM heap size and
> > > the memory size used by Lucene.
> > >
> > > What I am getting at is that no matter however much ram I give my
> > > apps, Lucene can't utilize it. Is that right?
> > >
> > > What about the ByteBufferDirectory? Can this specific directory
> > > utilize the 2GB memory I grant to the app?
> > >
> > > On Mon, Jun 4, 2012 at 10:58 PM, Jason Rutherglen <
> > > jason.rutherglen@gmail.com> wrote:
> > >
> > > > If you want the index to be stored completely in RAM, there is the
> > > > ByteBuffer directory [1]. Though I do not see the point in putting
> > > > an index in RAM, it will be cached in RAM regardless in the OS
> > > > system IO cache.
> > > >
> > > > 1.
> > > >
> > > https://github.com/elasticsearch/elasticsearch/blob/master/src/main/ja
> > > va/org/apache/lucene/store/bytebuffer/ByteBufferDirectory.java
> > > >
> > > > On Mon, Jun 4, 2012 at 10:55 AM, Cheng <zhoucheng2008@gmail.com>
> > wrote:
> > > > > My indexes are 500MB+. So it seems like that RAMDirectory is not
> > > > > good
> > > for
> > > > > that big a size.
> > > > >
> > > > > My challenge, on the other side, is that I need to update the
> > > > > indexes
> > > > very
> > > > > frequently. So, do you think MMapDirectory is the solution?
> > > > >
> > > > > Thanks.
> > > > >
> > > > > On Mon, Jun 4, 2012 at 10:30 PM, Jack Krupansky <
> > > jack@basetechnology.com
> > > > >wrote:
> > > > >
> > > > >> From the javadoc for RAMDirectory:
> > > > >>
> > > > >> "Warning: This class is not intended to work with huge indexes.
> > > > Everything
> > > > >> beyond several hundred megabytes will waste resources (GC
> > > > >> cycles),
> > > > because
> > > > >> it uses an internal buffer size of 1024 bytes, producing millions
> > > > >> of byte[1024] arrays. This class is optimized for small
> > > > >> memory-resident indexes. It also has bad concurrency on
> multithreaded
> > environments.
> > > > >>
> > > > >> It is recommended to materialize large indexes on disk and use
> > > > >> MMapDirectory, which is a high-performance directory
> > > > >> implementation
> > > > working
> > > > >> directly on the file system cache of the operating system, so
> > > > >> copying
> > > > data
> > > > >> to Java heap space is not useful."
> > > > >>
> > > > >> -- Jack Krupansky
> > > > >>
> > > > >> -----Original Message----- From: Cheng
> > > > >> Sent: Monday, June 04, 2012 10:08 AM
> > > > >> To: java-user@lucene.apache.org
> > > > >> Subject: RAMDirectory unexpectedly slows
> > > > >>
> > > > >>
> > > > >> Hi,
> > > > >>
> > > > >> My apps need to read from and write to some big indexes
> frequently.
> > > So I
> > > > >> use RAMDirectory instead of FSDirectory, and give JVM about 2GB
> > > > >> memory size.
> > > > >>
> > > > >> I notice that the speed of reading and writing unexpectedly slows
> > > > >> as
> > > the
> > > > >> size of the indexes increases. Since the usage of RAM is less
> > > > >> than
> > > 20%,
> > > > I
> > > > >> think by default the RAMDirectory doesn't take advantage of the
> > > memory I
> > > > >> assigned to JVM.
> > > > >>
> > > > >> What are the steps to improve the reading and writing speed of
> > > > >> RAMDirectory?
> > > > >>
> > > > >> Thanks!
> > > > >> Jeff
> > > > >>
> > > > >>
> > > >_____________________________________________
> > > **_____________________________________________
> > > **---------
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> > > > >> java-user-help@lucene.apache.**org<
> > > > java-user-help@lucene.apache.org>
> > > > >>
> > > > >>
> > > >
> > > >_____________________________________________
> > >
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> > > >
> > > >
> > >
> > >
>
>
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