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From J Chris Anderson <jch...@gmail.com>
Subject Re: _compact on 0.10.0 <> availability
Date Tue, 13 Apr 2010 16:39:07 GMT

On Apr 13, 2010, at 9:31 AM, till wrote:

> Hey devs,
> 
> I'm trying to compact a production database here (in hope to recover
> some space), and made the following observations:
> 
> * the set is 212+ million docs
> * currently 0.8 TB in size
> * the instance (XL) has 2 cores, one is idle, the other maybe utilized at 10%
> * memory - 2 of 15 GB taken, no spikes
> * io - well it's EBS :(
> 
> When I started _compact read operations slowed down (I'll give you 20
> Mississippi's for something that loads instantly otherwise).
> Everything "eventually" worked, but it slowed down tremendously.
> 
> I restarted the CouchDB process and everything is back to "snap".
> 
> Does anyone have any insight on why that is the case?

I'm guessing this is an EBS / EC2 issue. You are probably saturating the IO pipeline. It's
too bad there's not an easy way to 'nice' the compaction IO.

If you got unlucky and are on a particularly bad EBS / EC2 instance, you might do best to
start up a new Couch in the same availability zone and replicate across to it. This will accomplish
more-or-less the same effect as compaction.

> 
> Till


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