Re: Why is my mon store.db is 220GB?

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On 08/02/2013 12:15 AM, Jeppesen, Nelson wrote:
Thanks for the reply, but how can I fix this without an outage?

I tired adding 'mon compact on start = true' but the monitor just hung. Unfortunately this is a production cluster and can't take the outages (I'm assuming the cluster will fail without a monitor). I had three monitors I was hit with the store.db bug and lost two of the three.

I have tried running with 0.61.5, .0.61.7 and 0.67-rc2. None of them seem to shrink the DB.

My guess is that the compaction policies we are enforcing won't cover the portions of the store that haven't been compacted *prior* to the upgrade.

Even today we still know of users with stores growing over dozens of GBs, requiring occasional restarts to compact (which is far from an acceptable fix). Some of these stores can take several minutes to compact when the monitors are restarted, although these guys can often mitigate any down time by restarting monitors one at a time while maintaining quorum. Unfortunately you don't have that luxury. :-\

If however you are willing to manually force a compaction, you should be able to do so with 'ceph-mon -i FOO --compact'.

Now, there is a possibility this is why you've been unable to add other monitors to the cluster. Chances are that the iterators used to synchronize the store get stuck, or move slowly enough to make all sorts of funny timeouts to be triggered.

I intend to look into your issue (especially the problems with adding new monitors) in the morning to better assess what's happening.

  -Joao



Nelson Jeppesen
    Disney Technology Solutions and Services
    Phone 206-588-5001

-----Original Message-----
From: Mike Dawson [mailto:mike.dawson@xxxxxxxxxxxx]
Sent: Thursday, August 01, 2013 4:10 PM
To: Jeppesen, Nelson
Cc: ceph-users@xxxxxxxxxxxxxx
Subject: Re:  Why is my mon store.db is 220GB?

220GB is way, way too big. I suspect your monitors need to go through a successful leveldb compaction. The early releases of Cuttlefish suffered several issues with store.db growing unbounded. Most were fixed by 0.61.5, I believe.

You may have luck stoping all Ceph daemons, then starting the monitor by itself. When there were bugs, leveldb compaction tended work better without OSD traffic hitting the monitors. Also, there are some settings to force a compact on startup like 'mon compact on start = true' and mon compact on trim = true". I don't think either are required anymore though. See some history here:

http://tracker.ceph.com/issues/4895


Thanks,

Mike Dawson
Co-Founder & Director of Cloud Architecture Cloudapt LLC
6330 East 75th Street, Suite 170
Indianapolis, IN 46250

On 8/1/2013 6:52 PM, Jeppesen, Nelson wrote:
My Mon store.db has been at 220GB for a few months now. Why is this
and how can I fix it? I have one monitor in this cluster and I suspect
that I can't  add monitors to the cluster because it is too big. Thank you.



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--
Joao Eduardo Luis
Software Engineer | http://inktank.com | http://ceph.com
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