one minute polling doesn't actually run at 1 minute

[thisted]

I'm using spine

Polling interval is set at 1 minute
Cron interval is set at 5 minutes

This isn't a huge deal, but does seem like it could cause some issues. I've noticed that as the cron job gets further and further into a 5 minute period the start time of the polls gets further and further off from what I believe their start time is supposed to be, this is purely based on me watching task manager and correlating cpu usage to the clock.

In my most recent instance cpu usage spike at exactly 11:00:00, then the next time it started at 11:01:06...see below for full 5 minutes.

11:00:00
11:01:06
11:02:10
11:03:15
11:04:19

11:05:00


Attached is a screen shot of my taskmanager. If you look at the memory usage the poller start time drift is easy to see.



While my poll times are generally under 30 seconds....

Code: Select all

07/31/2009 11:05:20 AM - SYSTEM STATS: Time:20.2958 Method:spine Processes:8 Threads:16 Hosts:257 HostsPerProcess:33 DataSources:3801 RRDsProcessed:2274
07/31/2009 11:04:40 AM - SYSTEM STATS: Time:21.4638 Method:spine Processes:8 Threads:16 Hosts:257 HostsPerProcess:33 DataSources:3802 RRDsProcessed:2279
07/31/2009 11:03:34 AM - SYSTEM STATS: Time:20.3084 Method:spine Processes:8 Threads:16 Hosts:257 HostsPerProcess:33 DataSources:3802 RRDsProcessed:2277
07/31/2009 11:02:29 AM - SYSTEM STATS: Time:20.5435 Method:spine Processes:8 Threads:16 Hosts:257 HostsPerProcess:33 DataSources:3802 RRDsProcessed:2271
07/31/2009 11:01:25 AM - SYSTEM STATS: Time:20.4162 Method:spine Processes:8 Threads:16 Hosts:257 HostsPerProcess:33 DataSources:3802 RRDsProcessed:2276
07/31/2009 11:00:20 AM - SYSTEM STATS: Time:20.5065 Method:spine Processes:8 Threads:16 Hosts:257 HostsPerProcess:33 DataSources:3802 RRDsProcessed:2274

...this drift does start encroaching on the hard 11:05:00 start time.

any ideas why this may be happening?

[BSOD2600]

I don't believe a few seconds will be an issue, since rrdtool has mechanisms to compensate for such a thing. That stuff is documented in its manual somewhere.

[thisted]

My concern isn't about rrdtool, but rather the poller not completing its 5th poll before the cron job starts the poller.php process again.

By the time I get to the 5th poll in that cycle I effectively have only 40 seconds to complete the poll instead of 60.

I was just wondering if anyone else has noticed this and if there's a way to tell why it isn't starting at exactly 1 minute intervals.

[ARC1450]

My concern isn't about rrdtool, but rather the poller not completing its 5th poll before the cron job starts the poller.php process again.

By the time I get to the 5th poll in that cycle I effectively have only 40 seconds to complete the poll instead of 60.

I was just wondering if anyone else has noticed this and if there's a way to tell why it isn't starting at exactly 1 minute intervals.

I've noticed this myself (that sometimes the poller doesn't start right on the nose of the minute), and I do have the issue with the poller getting out-of-sync a lot.

That said, I have a feeling it wouldn't be as much of an issue with Linux, but unfortunately, my organization is quite anti-OSS (which is why I keep Cacti in the dark around here).