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From Peter Schuller <peter.schul...@infidyne.com>
Subject Re: what are ways to keep the SSTable Count down low
Date Mon, 20 Sep 2010 21:53:34 GMT
> How do you set the compaction threshold from storage-conf.xml? is this possible?

Not in 0.6 I believe, but I believe this recently went into trunk for
the upcoming 0.7.

> What is the consensus on a basic Key-Value store of setting the
> compactionthreshold min/max from
>
> ./nodetool --host=localhost --port=8181 getcompactionthreshold
> Current compaction threshold: Min=4, Max=32
>
> to say something like 2/5 ?

I make no claims about consensus, but in general if compaction is
affecting your node so adversely that it's effectively going offline
for the duration, while tweaking those settings may affect e.g.
frequency of compactions, it won't really fundamentally mitigate their
effects when they do happen.

I am curious about and other cases where people have sever problems
with compaction. In particular, what kind of row/column sizes are we
talking about? I would expect compaction to be a bigger killer for
data sets where I/O becomes the bottleneck rather than CPU (which
would tend to mean larger rows with fewer columns, meaning less CPU
bound compaction). It would be interest to confirm whether this is the
case.

There is some ongoing work to mitigate the impact of compaction and it
would be interesting to gather reports about the nature of the
problems people are having with it.

Have you observed 'iostat -x 1' or similar during compaction? Is the
underlying storage maxed out? What kind of I/O load do you normally
see due to regular traffic when compaction is not happening?

-- 
/ Peter Schuller

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