max_concurrent_checks=0 not working on 3.2.1 (maybe earlier versions, too)?

[Max]

Your server can only run so many checks at once, so setting it to 0
only says 'cap parallel check limits by what the CPU can do.'

On our dual quad-core CPU hosts with 8 GB RAM we get about 350 checks
running in parallel max at any given instant after restart; 90-92% of
our checks take less than 1 second to complete (most are SNMP-based).

We do attempt to have as many checks run as possible by setting
max_concurrent to 0 and by tweaking the next check time for all checks
to be the same second so that Nagios does attempt to run as many
processes as it possibly can at once.

Were you actually seeing your system start up 10,000 processes at once
with max_concurrent_checks set to 10,000?  That would be perfectly
reasonably if this were an Erlang-based system :), if you are getting
that number of processes at a given timel at the OS level, what kind
of system are you running on?  Impressive.

- Max

On Wed, Apr 14, 2010 at 4:03 PM, Cary Petterborg
<PetterborgCa at ldschurch.org> wrote:
> We have been experimenting with 3.2.1 before deploying it in our production environment. When we first started up Nagios 3.2.1 with max_concurrent_checks=0 (which the documentation says should put no limit on the number of concurrent checks), we only got about 200 checks completed per minute. Since we have 37,600 services, this led to quite a high latency.
>
> It attempting to increase the number of checks I decided to play with max_concurrent_checks to see what would result. I went from 0 to 1000, then to 10,0000, then to 100,000 then to 1,000,000(+) for the value. It increased the number of checks per minute with each larger number, until I got to 1,000,000, where it no longer made any difference.
>
> So, my conclusion is that max_concurrent_checks=0 is not working properly. Can anyone else verify that this is the case?
>
>
>
> Cary Petterborg
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