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From stephen bartell <>
Subject Re: random couch crash
Date Tue, 07 Aug 2012 20:01:09 GMT
I'll consider delayed_commits.

The database was 85MB before compaction. We ran compact and it was still 85Mb.  So compact
didn't work.  The same db on other servers will compact ~10x its original size.

> I strongly suggest disabling delayed_commits on general principles (what's written should
stay written). Are you able to compact the database(s) that give this error?
> B.
> On 7 Aug 2012, at 18:42, stephen bartell wrote:
>> delayed_commits = true
>> Stephen Bartell
>> On Aug 7, 2012, at 10:39 AM, Robert Newson wrote:
>>> Are you running with delayed_commits=true or false?
>>> B.
>>> On 7 Aug 2012, at 18:27, stephen bartell wrote:
>>>>> Hi Stephen,
>>>>> Can you tell us anymore about the context, or did you start seeing these
in the logs?
>>>> Sure, here's some context.  This couch is part of a demo server.  It travels
a lot and is cycled a lot.  There is one physical server, it consists of nginx (serving web
apps and reverse proxying for couch), couchdb for persistence, and numerous programs which
read and write to couch.  Traffic on couch can get very heavy.
>>>> I didn't first see this in the logs.  Some of the web apps would grind to
a halt, nginx would return 404, and then eventually couch would restart.  This would happen
every couple of minutes. 
>>>>> By chance do you have a scenario that reproduces this? Was this db compacted
or replicated from elsewhere?
>>>> I wish I had a pliable scenario other than sending the server through taxi
cabs, airlines, and pulling the power cord several times a day.  We haven't seen this on any
of our production servers.
>>>> This server was not subject to any replication.  Most databases on it are
compacted often.  
>>>> Last night we were able to drill down to one particular program which was
triggering the crash.  One by one, we backed up, deleted, and rebuilt the databases that program
touched.  There was one database which seemed to be the culprit, lets call it History.  History
is a dumping ground for stale docs from another db. History is almost always written to, and
rarely read from.   We don't compact History since all docs in it are one revision deep. 
We never replicate to or from it.  The only reason we deem History the culprit is because
after rebuilding it, there hasn't been a crash for over 12 hours.
>>>> I have an additional question.  Is it possible to turn couch logging off
entirely, or would redirecting to dev/null suffice?  When couch would crash, hundreds of MB
of crap would get dumped to the log. ( {{badmatch,{ok,<<32,50,48,48,10 … 'hundreds
of MB of crap' … ,0,3,232>>}}).  Right when this dump occurred, the cpu spiked and
the server began its downward descent. 
>>>> Best
>>>>> Thanks,
>>>>> Bob
>>>>> On Aug 7, 2012, at 2:06 AM, stephen bartell <>
>>>>>> Hi all, could some one help shed some light on this crash I'm having.
 I'm on v1.2, ubuntu 11.04.  
>>>>>> [Mon, 06 Aug 2012 18:29:16 GMT] [error] [<0.492.0>] ** Generic
server <0.492.0> terminating 
>>>>>> ** Last message in was {pread_iolist,88385709}
>>>>>> ** When Server state == {file,{file_descriptor,prim_file,{#Port<0.2899>,79}},
>>>>>>                         93302896}
>>>>>> ** Reason for termination == 
>>>>>> ** {{badmatch,{ok,<<32,50,48,48,10 … huge dump … ,0,3,232>>}},
>>>>>> [{couch_file,read_raw_iolist_int,3},
>>>>>> {couch_file,maybe_read_more_iolist,4},
>>>>>> {couch_file,handle_call,3},
>>>>>> {gen_server,handle_msg,5},
>>>>>> {proc_lib,init_p_do_apply,3}]}
>>>>>> I'm not too familiar with erlang, but what I gathered from the src
was `pread_iolist` function is used when reading anything from the disk.  So I think this
might be a corrupt db problem.
>>>>>> Thanks,
>>>>>> Stephen Bartell

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