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

Cary Petterborg PetterborgCa at
Wed Apr 14 22:03:43 CEST 2010

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
ICS Monitoring
The Church of Jesus Christ of Latter-day Saints
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Email:  petterborgca at
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