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From Lance Norskog <>
Subject Re: RAM or SSD...
Date Thu, 19 Jul 2012 06:04:48 GMT
> You do not want to store 30 G of data in the JVM heap, no matter what library does this.
MMapDirectory does not store data in the JVM heap. It lets the
operating system manage the disk buffer space. Even if the JVM says "I
have 30G of memory space", it really does not. It only has address
space allocated by the  OS but no memory.

On Wed, Jul 18, 2012 at 10:39 PM, Toke Eskildsen <> wrote:
> On Wed, 2012-07-18 at 17:50 +0200, Dragon Fly wrote:
>> If I want to improve performance, which of the following is better and why?
>> 1. Buy a machine with a lot of RAM and use a RAMDirectory for the index.
> As others has pointed out, MMapDirectory should work better than
> RAMDirectory. I am sure it will work fine with a relative small index
> such as yours. However, it does not scale that well with index size.
>> 2. Put the index on a solid state drive.
> Why anyone buys computers without SSD's is a mystery to me. Use SSDs for
> the small low-latency stuff and a secondary spinning drive for the large
> slow stuff. Nowadays, a 30GB index (or 100GB for that matter) falls into
> the small low-latency bucket. SSDs speeds up almost everything, saves
> RAM and spares a lot of work hours optimizing I/O-speed.
> Regards,
> Toke Eskildsen
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Lance Norskog

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