Re: Weird spike in System time every 5:00 minutes...

From: Nicholas Dronen (ndronen_at_io.frii.com)
Date: 08/29/03 

Date: 29 Aug 2003 02:28:17 GMT

Don Whitlow <dwhitlow1@wi.rr.com> wrote:
DW> Hi All,

DW> I have what I consider to be an odd behavior on some of my AIX boxes.
DW> So far, on most of the AIX servers I have that are running Sybase, I
DW> see a brief spike every 5 minutes in system time, either via sar, or
DW> through topas. In general, the spikes go up to anywhere between 20 and
DW> 40% and last for only a couple seconds. However, the 'weird' part is
DW> that it is just about always on the '5's, meaning 12:00, 12:05, 12:10,
DW> etc. etc... See sar output below:

DW> 16:09:44 %usr %sys %wio %idle
DW> 16:00:45 25 6 1 67
DW> 16:00:46 20 6 0 73
DW> 16:00:47 26 6 2 67
DW> 16:00:48 32 13 2 54
DW> 16:00:49 17 13 7 62
DW> 16:00:51 32 27 7 34
DW> 16:00:52 29 47 17 7
DW> 16:00:53 22 46 14 17
DW> 16:00:54 40 23 3 34
DW> 16:00:55 38 14 0 47

DW> I realize this could be something Sybase is doing every 5 minutes, but
DW> our DBAs can't find or think of anything that would sync itself to
DW> happening not only at given intervals, but set times as well. I
DW> figured I would put this out to the group just to see if maybe AIX
DW> does something every 5 minutes. Maybe process cleanup, memory
DW> reclamation, fs io cache writeouts, or something like that?

Syncd usually runs every 60 seconds, but if Sybase is configured
to use raw devices, syncd doesn't really apply.

DW> It might not be anything to worry about. At this point I think it's
DW> more of a curiosity. But, any thoughts on what it may be would be
DW> appreciated.

Is the monitor server running? (I know little about it but I can
imagine it polling ASE every once in a while, though not in a way
that causes a moderate spike such as yours.)

Check all crontabs on the machine for scripts that contain isql
commands. I wouldn't be surprised if there was a cron job that
ran a fairly intense query every 5 minutes.

How recent is your version of ASE? I know at least a recent
version has an internal scheduling agent. The name escapes
me, but that might be the "culprit," too.

Regards,

Nicholas 

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