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From db>
Subject Re: bigcouch restarts when update handler parses a lot of data
Date Tue, 18 Feb 2014 17:21:25 GMT
Hello, this message is just to say that we found out that the issue is not a
memory or application bug, but rather a lack of knowledge about how strings
are handled in Erlang and the high amount of memory needed to represent them.

Thanks anyway!


db spewed 2.6K bytes:
> Hello.
> I'm working on the LEAP project ( and we've been using
> cloudant's bigcouch as a backend for one part of our infrastructure.
> Latest available bigcouch debian package is built on top of a fork of couchdb
> 1.1.1. Along the development, we stumbled upon some bugs that are already
> solved in newer versions of couchdb, and even patched bigcouch code to
> generate a new debian wheezy package (thanks to a lot of help from #cloudant
> people).
> Despite that, there's one bug which we could not solve yet and people on
> #cloudant said it would be good to have the conversation on this list.
> The bug description goes like this:
>   bigcouch restarts on PUTs to a design document update handler that calls
>   JSON.parse(req.body), when the PUT request body is "large".
> One strange thing is that "large" differs from server to server. On my local
> machine it works fine, i.e. I can use the update handler and PUT bodies up to
> the configured max_document_size (which defaults to 64 MB). On 3 distinct
> remote nodes we have, the maximum body sizes that make the server restart are
> different, but consistent, that is, the limit is always the same for one node
> (37, 26 and 8 MB).
> Some info that might help the diagnosis:
> * Tracing the request handling, I found that the last function that is called is
>   mochijson2:encoder(), and then the server restarts.
> * I tried changing resource limits for the bigcouch process, but made no
>   difference.
> * These are the first 150 KB of the erl_crash.dump for one of the restarts
>   (the whole thing is about 100 MB):
>   It is clearly trying to allocate a lot more memory than it should.
> * As rnewson told me on #cloudant that this might be related to memory bugs
>   on erlang, I built bigcouch using the latest erlang from wheezy-backports,
>   but i got the same behaviour. These are the first 150 KB of erl_crash.dump
>   for bigcouch built with R16B03:
> * This is the design doc update handler that calls JSON.parse(req.body) we are
>   using:
> Kind people on IRC have been helping with this and other issues, and asked to
> continue the conversation on this list. I know that cloudant's bigcouch is
> being merged into couchdb code, and hope that this problem may either (1) be
> already resolved, or (2) be some stupid thing I'm missing, or (3) still exist
> and we might help solve it.
> If there's any other info I can provide, please let me know.
> Thanks a lot for any help!
> db.
> -- 
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