Linux – DB Server Disk I/O utilization

One good way to debug why the command being executed is not returning any valid output is to use strace. For example, I just had a problem running the check_linux_raid command via NRPE.

Run strace -f -p <nrpe pid>, and then execute the command manually from the system running nagios (e.g. /usr/lib64/nagios/plugins/check_nrpe -H remotename -c commandname -a arg1 arg2 ...).

Scan the output of strace for errors, such as permission denied or other similar errors that may occur. For example, in my case, selinux was denying permission to a file when running from the remote machine, even though that user has local access to that file.

There are no common rules

Performance rules need to be set by business & technical objectives - not arbitrary ones.

What performance issue are you trying to resolve or prevent?

Metrics do not equate performance and often have little to to do with business or even technical objectives.

Typically I look at two aspects of performance.

• What metrics do I need to monitor that meet performance objectives?
• How much resource overhead do I wish to maintain to assure I meet these performance objectives.

Focusing purely on database resource metrics in absence of other data is likely not very useful. These metrics need context - otherwise it is just premature optimization.

Metrics like these are useful for capacity planning if you know your utilization rates.

So maybe more important questions would be:

• At peak usage levels is my application performing within acceptable limits?
• At peak usage, what is my resource utilization.?
• With the expected growth, what will be my resource utilization?

Too often I find people focus on what I call ping, power and pipe (CPU/Disk/RAM). Rarely are these the important things to focus on.

Getting data and setting goals to the questions above will help you make scalability decisions with both technical and business justifications.