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From Anshum <>
Subject Re: Regarding RAMDirectory, FSDirectory, tmpFS...
Date Mon, 30 Jun 2008 10:18:52 GMT
Hi Devashish,

The difference between these modes of operation would be that firsly,
RAMDirectory and FSDirectory on one hand are implementations of the
directory class of lucene.
Lucene's directory is just a flat list of files and an FSDirectory is a just
a file system (straightforward) implementation of the same where is
RAMDirectory is a memory (RAM) based implementation of the same.
tmpFS on the other hand is a file system and so is an OS level thing with
nothing to do at all with lucene/java. This means that there is no limit to
allocating a tmpfs (in terms of size).
When we use RAMDirectory, the JVM would load the index into its memory (and
use the memory allocated to it). This might be a cause of issue as 32 bit
JVM do not allow appropriation of over 2 gigs of total memory to a single
JVM instance (out of which only 1.2 gigs would be resident memory).
While in both the java Directory implementations the JVM handles most of the
stuff e.g. loading unloading indexes to/from the memory, in case of tmpfs we
have to manual do the task.

Hope that clears your questions! :)


On Mon, Jun 30, 2008 at 1:27 PM, Devashish <> wrote:

> What is the difference between these three modes of operating with
> lucene... And are there any other modes/ways of operation also, using
> which we can more effectively run applications with lucene.
> I have heard there is also something called 'Memory' in contrib
> directory of lucene source package which can also be used.
> Can you please let me know how these are different from each other/how
> do each of these work..
> Regards,
> --
> Devashish <>
> Naukri Tech
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The facts expressed here belong to everybody, the opinions to me.
The distinction is yours to draw............

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