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From Oliver Oli <oliver.oli+0...@gmail.com>
Subject Re: mochiweb socket options discriminating against slow connections
Date Fri, 06 Nov 2009 10:35:51 GMT
sometimes i'm getting connection errors from couchapp over a slow DSL
connection. is this related?

On Wed, Nov 4, 2009 at 10:42 PM, Adam Kocoloski <kocolosk@apache.org> wrote:
> Hi, Zachary Zolton, Joe Williams and I stumbled on an awkward part of
> CouchDB's (actually MochiWeb's) configuration that makes working over a slow
> connection problematic.  When receiving a large unchunked upload, MochiWeb
> calls
>
> gen_tcp:recv(Socket, Length = 1048576, Timeout = 10000)
>
> which says "pull 1MB off the socket in 10 seconds, or timeout".  This is a
> bit crazy, as we'd definitely like to support e.g. replication with CouchDB
> servers over slower links than 100KB/s.
>
> I tried to do a little digging to see what recourse we have.  We can of
> course play the tuning game adjusting the length and timeout until we're
> happy, but I think it'd be nicer to never timeout a connection that is still
> sending data.  From the gen_tcp man page
>
>> The Length argument is only meaningful when the socket is in raw
>> mode and denotes the number of bytes to read. If Length = 0, all
>> available bytes are returned. If  Length  >  0,  exactly  Length
>> bytes  are  returned, or an error; possibly discarding less than
>> Length bytes of data when the socket gets closed from the  other
>> side.
>>
>> The  optional Timeout parameter specifies a timeout in millisec-
>> onds. The default value is infinity.
>
> I don't know what the behavior is when there are 0 bytes available on the
> socket -- does gen_tcp:recv just keep returning 0 and leave it to us to
> implement the timeout, or can we do something like
>
> gen_tcp:recv(Socket, 0, 10000)
>
> Best, Adam
>

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