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From CGS <cgsmcml...@gmail.com>
Subject Re: timeout hitting a database url after launching compaction
Date Mon, 17 Oct 2011 10:39:13 GMT
I don't suppose that's the developers' choice. That's more like W3C 
choice when they defined the standard codes. In your case, the code is 
returned by cURL (or whatever application you use for triggering the 
predicate GET). I am not so sure the developers can do anything about 
that because the database file on the disk is replaced with the new 
database file in which the history is no longer kept (if I understood 
well the compaction process). The only thing the developers may be able 
to do is to offer you a 404 code (file not found) during that time. But 
I suppose that's more alarming then 500. :)

Nevertheless, that's their choice and it's good that you provided this 
piece of information for the rest of us to know about it and to know how 
to handle these situations.

Cheers,
CGS



On 10/17/2011 10:29 AM, Paolo Negri wrote:
> I agree on the fact that what happens is pretty clear to explain, I
> still thought it would be useful for the developers to know since
> offering a 500 status code for a known system condition is probably
> something that can be improved.
>
> Thanks,
>
> Paolo
>
> On Mon, Oct 17, 2011 at 10:24 AM, CGS<cgsmcmlxxv@gmail.com>  wrote:
>> I am not developer, but it's quite logic, I may say. Once you started the
>> compaction, your CouchDB is not responsive while the database is preparing
>> for compaction. Triggering immediately GET, the web instance responds with
>> status code 500 (internal server error, meaning unresponsive server in this
>> case). So, nothing unusual in my opinion.
>>
>> Cheers,
>> CGS
>>
>>
>>
>>
>> On 10/17/2011 09:57 AM, Paolo Negri wrote:
>>> IO activity is not monitored, there's only one db on the couchdb
>>> instance and the described job is the only activity executed on this
>>> machine.
>>> Delaying the first request on the database url by 30 seconds did
>>> actually prevent the problem from happening again.
>>> So the issue seems to happen specifically at the moment right after
>>> compaction is started.
>>> The database is about 7GB big once compressed, the server is hosted on
>>> ec2 with the database directory placed on his own dedicated ephemeral
>>> storage.
>>>
>>> Thanks,
>>>
>>> Paolo
>>>
>>> On Fri, Oct 14, 2011 at 9:05 PM, Paul Davis<paul.joseph.davis@gmail.com>
>>>   wrote:
>>>> Do you monitor IO activity or system responsiveness when you're doing
>>>> this. I've seen some compactions wallop a system when it switches over
>>>> due to removing large old files and such. It doesn't sound like this
>>>> is big enough for that case but it might be something worth checking.
>>>>
>>>> On Fri, Oct 14, 2011 at 3:41 AM, Paolo Negri<paolo.negri@wooga.net>
>>>>   wrote:
>>>>> Dear list,
>>>>>
>>>>> We have a script that does the following (strictly sequentially)
>>>>>
>>>>> 1) update 300K docs in a db
>>>>> 2) launch compaction of the db
>>>>> 3) poll at a 30 sec frequency http://127.0.0.1:5984/database to know
>>>>> when compaction completed
>>>>>
>>>>> Last night we got a timeout error during 3, we think that this might
>>>>> be because the first polling (GET  http://127.0.0.1:5984/database) is
>>>>> done right after triggering compaction
>>>>>
>>>>> I thought the dev team might be interested in knowing that this is
>>>>> happening
>>>>>
>>>>> There's no other activity on the couchdb instance other than what
>>>>> described in this email.
>>>>>
>>>>> ERROR unexpectd response checking compaction db: {ok,"500",
>>>>>                                                  [{"Server",
>>>>>
>>>>> "CouchDB/1.3.0a-74613f5-git (Erlang OTP/R14B04)"},
>>>>>                                                   {"Date",
>>>>>                                                    "Fri, 14 Oct 2011
>>>>> 01:46:37 GMT"},
>>>>>                                                   {"Content-Type",
>>>>>                                                    "text/plain;
>>>>> charset=utf-8"},
>>>>>
>>>>>   {"Content-Length","350"},
>>>>>                                                   {"Cache-Control",
>>>>>                                                    "must-revalidate"}],
>>>>>
>>>>>
>>>>> <<"{\"error\":\"{timeout,{gen_server,call,[<0.21934.9>,{open_ref_count,<0.4090.13>}]}}\",\"reason\":\"{gen_server,call,\\n
>>>>>    [couch_server,\\n     {open,<<\\\"backup\\\">>,\\n
>>>>> [{user_ctx,\\n              {user_ctx,null,\\n
>>>>> [<<\\\"_admin\\\">>],\\n<<\\\"{couch_httpd_auth,
>>>>> default_authentication_handler}\\\">>}}]},\\n     infinity]}\"}\n">>}
>>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Paolo
>>>>>
>>>
>>
>
>


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