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Date: Tue, 12 Feb 2013 06:46:26 +0000
From: Eric Charles <eric@apache.org>
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To: James Users List <server-user@james.apache.org>
Subject: Re: Using connectionBacklog
References: <511920A9.5000004@nitorgroup.com>
In-Reply-To: <511920A9.5000004@nitorgroup.com>
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Hi,

If you set backlog=1, the socket can not queue more than one request at 
a time. So if the socket is already busy with one connection, a second 
connection request will be simply rejected. The backlog property is 
given to netty for its bootstrap.

The connectionLimit is implemented with Netty handlers which rejects 
connection if you have already more open connection than the given number.

Thx, Eric


On 11/02/2013 16:47, Phillip Odam wrote:
> Can anyone confirm successful use of connectionBacklog for the smtp
> service on james 3.0 beta4 (or any v3). Successful use of
> connectionBacklog for any of the other services e.g. imap, lmtp and pop3
> is also of interest as under the covers the code is all common.
>
> Firstly I gather the connectionBacklog setting is controlling the
> backlog just as is done in
> http://docs.oracle.com/javase/6/docs/api/java/net/ServerSocket.html
>
> Secondly comparing the code
>   -
> http://svn.apache.org/repos/asf/james/protocols/trunk/netty/src/main/java/org/apache/james/protocols/netty/AbstractAsyncServer.java
>
>   -
> http://svn.apache.org/repos/asf/james/protocols/tags/protocols-1.6.2/netty/src/main/java/org/apache/james/protocols/netty/AbstractAsyncServer.java
>
>
> reports no differences so apart from the different versions of netty
> between beta4 and where beta5 development is there should be no
> difference with the backlog between beta4 and the current development
> stream.
>
>
> Changing the connectionBacklog value does cause the startup log entry
> (SMTP Service connection backlog is: XXX) to change accordingly, however...
>
> SETUP
> -----
>
> connectionBacklog = 1
> connectionLimit = 1
>
> TESTING
> -------
>
> With two command lines, use telnet to connect to the smtp service, the
> first telnet instance will establish a connection.
>
> The second instance reports back immediately that a connection can not
> be established, whereas I would expect the second instance to hang and
> either establish a connection when the first telnet instance disconnects
> or a timeout occurs.
>
>
> Testing thus far has not been in a controlled environment so the backlog
> issue may well not be with james, but before I go much further I wanted
> to see what anyone else out there is seeing.
>
> Thanks
> Phillip
>
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