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From Ken Krugler <>
Subject Re: How much ram can Solr use?
Date Thu, 28 Sep 2006 03:27:24 GMT
>On 9/27/06, Kevin Lewandowski <> wrote:
>>On the performace wiki page it mentions a test box with 16GB ram. Did
>>anything special need to be done to use that much ram (with the OS or
>>java)? Would Solr on a system with Linux x86_64 and Tomcat be able to
>>use that much ram? (sorry, I don't know Java so I don't know if there
>>are any limitations there).
>Yep, works fine....  We don't use the full 16GB for the java heap
>though because:
>- you want to leave RAM for the OS cache of the index files
>- bigger heaps = longer gc pauses (at least with Java5).

Yes, we came to exactly the same conclusion.

You could try to use all of that RAM in the JVM, and load all of the 
index with a RAMDirectory (or MMapDirectory), but both of those wound 
up being slower than the configuration where we had a smaller JVM and 
relied more on the OS-level cache to make index accesses really fast.

One trick I've heard is to do cat <path to Lucene index 
directory>/_*.* > /dev/null to force all of the index data into the 
OS cache.

-- Ken
Ken Krugler
Krugle, Inc.
+1 530-210-6378
"Find Code, Find Answers"

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