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From "Stefan Bodewig (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4NET-415) RemoteSyslogAppender may block for ARP resolution + Improvement Strict RFC3164
Date Sun, 19 Jan 2014 06:13:19 GMT

    [ https://issues.apache.org/jira/browse/LOG4NET-415?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13875826#comment-13875826
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Stefan Bodewig commented on LOG4NET-415:
----------------------------------------

Thanks for your persistence Jose Luis

First of all I'd wish to find more time :-(

Well, 

* I'd leave all async stuff out and rather try to get one of the proposed general purpose
AsyncAppenders into shape.
* I'd make non-blocking an option but change the documentation to clearly state this may lead
to lost logs
* I'd try to find a better name for the StrictRFC3164 property that better says what it does.
 Then again I've never been good at names.

At least for the StrictRFC3164 part we could use a unit test or two, I don't think writing
tests for the blocking part will be easy.  You don't really need to resubmit your patch, I
can modify it myself, but you may be faster than me.

> RemoteSyslogAppender may block for ARP resolution + Improvement Strict RFC3164
> ------------------------------------------------------------------------------
>
>                 Key: LOG4NET-415
>                 URL: https://issues.apache.org/jira/browse/LOG4NET-415
>             Project: Log4net
>          Issue Type: Bug
>          Components: Appenders
>    Affects Versions: 1.2.13
>         Environment: Any Windows environment
>            Reporter: Jose Luis Pedrosa
>              Labels: RemoteSyslogAppender
>         Attachments: LOG4NET-415.patch, MessageLostTest.cs, MessageLostTest.cs, MessageLostTestAsync.cs,
RemoteSyslogNonBlockingv2.patch
>
>
> Sending UDP packages may block for some time in specific circumstances:
> 1) Next hop in network level 3 can't be resolved by ARP.
> 2) Datagram size exceeds FastSendDatagramThreshold configured size.
> When sending packets bigger than FastSendDatagramThreshold, the OS waits until the packet
is actually sent, if the If the syslog (or the next hop to reach the syslog) is in the same
VLAN/Subnet the OS tries to resolve by ARP the Ip of the configured syslog, this may take
up to 3 seconds, slowing down the whole application, which in some cases can lead to outages
(timeouts, DB locks...).
> Also the fact that each carriage return generates the headers of the packet again, that
can lead to a significant overhead in some scenarios, for instance when loggign HTTP requests
to a remote syslog, every header will go in a different message. Also some logging may require
characters that are now skipped in patch:  https://issues.apache.org/jira/browse/LOG4NET-370
> I'm adding a patch that
> 1) Moves the use of UDPClient to Non blocking sockets, which eliminates the blocking.

> 2) Adds a configuration field to decide if you want Strict RFC Behaviour or not (with
default Strict).
> Please your feedback, thanks in advance
> Jose Luis



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