Option append_to_file in nsca.cfg

[Wheeler, JF (Jonathan)]

> -----Original Message-----
> From: nagios-users-bounces at lists.sourceforge.net On Behalf Of Marc
Powell
> Sent: 13 March 2007 16:17
> 
> > -----Original Message-----
> > From: nagios-users On Behalf Of Wheeler, JF (Jonathan)
> > Sent: Tuesday, March 13, 2007 9:59 AM
> > To: nagios-users at lists.sourceforge.net
> > Subject: [Nagios-users] Option append_to_file in nsca.cfg
> > 
> > As I have said before my configuration consists of 1 master server
and 2
> > slaves with about 700 hosts and 16000 checks.  In the file nsca.cfg
> > which configures the nsca daemon, there is an append_to_file option
> > which is (by default) set to 0 for writing to the command file
rather
> > than 1 for appending to it.  Please would someone explain why
appending
> > to the command file is deprecated.  I ask because I can have several
> 
> Semi-educated commentary follows -- The 'command file' is more
properly
> named a 'command pipe'. It's not a real file and therefore appending
to
> it makes no sense. A pipe is essentially a FIFO buffer. Data is
written
> to it by one process and read by another in a sequential fashion. If
the
> reading process can't keep up with the writing process, your kernel
will
> buffer the writes up to a point depending on the OS. For linux kernel
> < 2.6.11 the buffer was 4096 bytes. For > 2.6.11, the buffer is 65535
> bytes. Nagios also has its own internal buffers to help process the
pipe
> faster. With nagios-2.7, these are controlled by the
> external_command_buffer_slots option in nagios.cfg. You can also
control
> how often nagios checks for data in the pipe with the
command_check_interval
> setting. You certainly want that to be -1 and not
> every 4 seconds. -1 tells nagios to check as often as possible.
> 
> Depending on your check frequency, it sounds like nagios isn't able to
> keep up with your check submissions, almost certainly related to your
> checking the pipe every 4 seconds only. At ~100 bytes per check, you
> could only accept 40 results in 4 seconds before dropping. If you're
> doing 16,000 checks every 5 minutes that's ~213 check results every 4
> seconds. You can do the math based on your actual sizes/intervals...
> 
> Verify that you have a good amount of buffer slots (use nagiostats to
> see current utilization) and that you're checking external commands as
> fast as possible.
> 
> I'm only doing 1/4 of the passive checks you are so you may be hitting
> limits that I haven't experienced yet but it doesn't appear so at this
> point.

Sorry, I think that I have confused the discussion by not appreciating
the difference between service_reaper_frequency (which is 4 secs) and
command_check_interval (which is -1).
After restarting nagios this morning (Thur 15/03 - the master server had
panic'ed due to lack of memory), I issued the command "wc -l
/var/log/nagios/rw/nagios.cmd" and got the answer 1003 (this is command
pipe).  If I understand you correctly, there were 1003 commands in the
pipe waiting to be processed by the server (understandable as the master
server had just restarted and the slaves had plenty of commands waiting
to be processed), but the operation of command wc actually discarded
these commands by reading through the pipe.

At present I am running nagios 2.6.  I want to upgrade to nagios 2.8,
but as I also use ndoutils I need to compile the latest version of that
and update the SQL tables that it writes.  If the problem does not go
away with the latest version of the server, I will raise the issues
again, but nay other comments would be much appreciated.

Jonathan Wheeler
e-Science Centre
Rutherford Appleton Laboratory

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