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From "Ganesh" <>
Subject Re: Index size and performance degradation
Date Tue, 14 Jun 2011 09:58:33 GMT
Is it a bad idea to keep multiple shards in a single system?


----- Original Message ----- 
From: "Toke Eskildsen" <>
To: <>
Sent: Tuesday, June 14, 2011 12:58 PM
Subject: Re: Index size and performance degradation

> On Sun, 2011-06-12 at 10:10 +0200, Itamar Syn-Hershko wrote:
>> The whole point of my question was to find out if and how to make 
>> balancing on the SAME machine. Apparently thats not going to help and at 
>> a certain point we will just have to prompt the user to buy more hardware...
> It really depends on your scenario. If you have few concurrent requests
> and are looking to minimize latency, sharding might help; assuming you
> have fast IO and multiple cores. You basically want to saturate all
> available resources for all requests.
> On the other hand, if throughput is the issue, sharding on a single
> machine is counter-productive due to increased duplication and merging.
>> Out of curiosity, isn't there anything that we can do to avoid that? for 
>> instance using memory-mapped files for the indexes? anything that would 
>> help us overcome OS limitations of that sort...
> One standard advice for speeding up searches is using SSD's. Our
> (admittedly old) experiments puts SSD-performance near RAM. With the
> prices we have now, SSD's seems like an obvious choice for most setups.
> We tried a few performance tests at different index sizes and for us,
> index size vs. performance looked like the power law: Heavy performance
> degradation in the beginning, less later. It makes sense when we look at
> caching and it means that if you do not require stellar performance, you
> can have very large indexes on few machines (cue Hathi Trust).
> - Toke Eskildsen
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