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From "B. Todd Burruss" <>
Subject Re: cassandra not responding
Date Tue, 16 Mar 2010 21:57:45 GMT
i am just reading/writing 4k+/-1k of data to a single column in a single 
column family.  i do some writes of fresh data and some read/write of 
existing data.  i will end up in the 100 million row range, maintaining 
about a 2 million row of "hot data".  so i have small rows, but _lots_ 
of them.

so you are using row cache?  what setting?

what i find is that the OS cache is plenty good enough.  i have 48gb RAM 
per node and try to give the OS as much as possible by setting "-Xms1G 
-Xmx44G".  the Xmx is large because of what i'd seen with cassandra 
needing a lot of memory sometimes.  and in fact, you don't want to use 
too much JVM memory as GC will start to eat up your CPU time and cause 

what i don't like is it appears that once the JVM "commits" RAM to its 
process it never releases it.  at least i haven't seen it release.

Tom Chen wrote:
> Can you give some details about the use case that you are using 
> cassandra for? I am actually looking to store almost the data in the 
> same manner, except with more of a variance in data  1k to 5k with 
> about 20 million rows. 
> I have been benchmarking cassandra on 5 verses 6, and v6 has 
> significant speed improvements if I hit the cache (obviously memory 
> access verses random disk.)  Write performance in either version is 
> pretty damn good. 
> Tom

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