[syslog-ng]TCP transport reliability

[Balazs Scheidler]

> > Hello,
> >
> > > > I'm testing syslog-ng with TCP transport, and I'm a little surprised-
> > > > perhaps I'm doing something wrong? I'm finding severe message loss,
> > > > which I had imagined TCP would eliminate.
> > >
> > > I've reported the same thing on this list in the past.  Indeed, my
> > > machines can even lose messages when the input is a pipe and the output is
> > > a local file!
> >
> > And I replied that you are _not_ correct. Several times. Please stop
> > spreading misinformation.
> 
> Repeating yourself doesn't make you right.  Look at the code again:
> 
> 
>          if (self->queue_size == self->queue_max) {
>                  /* fifo full */
>                  ol_string_free(string);
>                  return ST_FAIL | ST_OK;
>          }
> 
> What do you think happens when this code is hit?  The log message is
> discarded and lost.  It cannot be read any other way.  When this block of
> code is executed, messages are lost.  Execution tracing shows that this
> block of code is sometimes executed.  Thus, messages will sometimes be
> lost.  QED.

You are right that messages may be lost in a special case.

 One of the design goals of
syslog-ng was that sending processes should never block. Have you ever had a
computer whose syslogd was blocked? Sending processes 

> 
> Your repeated assertions are no solution.  In practice, syslog-ng drops
> log messages.  I have seen it with my own eyes, and I have proved it
> logically above.  You have not given me any reason to believe otherwise.
> Your suggestion to raise the fifo size does not work for fast,
> steady-state log message generation.  I can raise the fifo size to
> 1,000,000 messages, and I get a syslog-ng process that consumes all
> available memory and still drops messages.
> 
> -jwb
> 
> 
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-- 
Bazsi
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