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From Edward Capriolo <edlinuxg...@gmail.com>
Subject Re: what are ways to keep the SSTable Count down low
Date Mon, 20 Sep 2010 19:32:49 GMT
On Mon, Sep 20, 2010 at 3:14 PM, Dathan Pattishall <dathanvp@gmail.com> wrote:
> How do you set the compaction threshold from storage-conf.xml? is this possible?
>
> 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 ?
>
>
> The next question is why do you want to change it?
>
> I noticed that all my outages are due to compaction. The SSTable count
> grows from 4-11 and then a compaction happens taking that server
> offline even with all the threshold tricks in cassandra.in.sh
> (-Dcassandra.compaction.priority=1). So, playing with this value seems
> to me to be the right course of action.
>

You should look at your memtable settings memtable flushes happen
because of either
1) time
2) size
3) activity
Why are they happening for you?

If you raise your memtable settings you will get larger memtables.
This results in larger sstables that will compact less often.

Lowering the compaction probably will not do what you want because
this will result in the same data being compacted again and again.
Remember the goal of minor compaction is to combine X like sized
SSTables.

If your nodes are going out during compaction they are likely
overtaxed. I had great luck with the compaction priority. 6.5 features
'dynamic snitch' which should help lead traffic away from compacting
nodes. You may want to give it a try.

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