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From Carlos Alvarez <>
Subject Re: Capacity problem with a lot of writes?
Date Thu, 25 Nov 2010 23:18:50 GMT
> When you say that it grows constantly, does that mean up to 30 or even
> farther?

My total data size is 2TB

Actually, I never see the count stable.  When it reached 30 I thinked
"I am reaching the default upper limit for a compaction, something
went wrong" and I went back to 1GB memtables (also, I saw bigger read

Well, I think you are right: I am CPU bounded on compaction, because I
see during compactions a single jvm thread which is almost all the
time in running state and the disk is not used beyond 50%.

> (A nice future improvement would be to allow for concurrent compaction
> so that Cassandra would be able to utilize multiple CPU cores which
> may mitigate this if you have left-over CPU. However, this is not
> currently supported.)

Yes, sure. I'd be happy to test, but I don't dare to alter the code :-)

I think that a partial solution would help: if the compaction
compacted to 'n' diferents new sstables (not one), the implementation
would be easier. I mean, the compaction would compact, for instance,
10 sstables to 2 (being 2 the level of paralelism). In this way, the
sstables count would remain eventually stable (although higher). What
do you think?


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