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From Adam Kocoloski <kocol...@apache.org>
Subject mochiweb socket options discriminating against slow connections
Date Wed, 04 Nov 2009 21:42:41 GMT
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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