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From Bryan Pendleton <bpendleton.de...@gmail.com>
Subject Re: Could use some thoughts on a problem with a query in production
Date Wed, 07 Jun 2017 13:46:40 GMT
Hi Brett,

Cache cleaning in general is a very I/O intensive activity, so I agree that
it is odd that your system appeared to be CPU busy during that time.

It's interesting that whatever it was, persisted for such a long time.

In the past, I have developed small operator scripts which collect system
information, which can be run by a simple monitoring tool and can keep a
history about the observations they make.

If you were to build and install such a monitoring system, you might be
able to develop more clues about the "larger picture" of activity on your
machine during that time period.

Sorry to be so vague and non-specific, but I find that retrospective
analysis of problems like this is VERY challenging.

Often, the best you can do is:
1) Try to figure out some way to make the problem happen on demand, so you
can cause it and observe it.
2) Instrument everything, and ensure you are preserving a history of your
instrumentation recordings, so that you can have a mountain of detail when
those rare events occur.

It strikes me as being like high-energy physics, where your experiment
generates volumes of data, and it takes weeks or months of analysis
afterward to figure out what actually occurred.

Not that I'm much good at high-energy physics, either, I'm afraid. :)

bryan

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