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Re: [pcp] pcp update: json pmda

To: Nathan Scott <nathans@xxxxxxxxxx>, Mark Goodwin <mgoodwin@xxxxxxxxxx>, "Frank Ch. Eigler" <fche@xxxxxxxxxx>
Subject: Re: [pcp] pcp update: json pmda
From: David Smith <dsmith@xxxxxxxxxx>
Date: Wed, 10 Jun 2015 10:15:51 -0500
Cc: pcp developers <pcp@xxxxxxxxxxx>
Delivered-to: pcp@xxxxxxxxxxx
In-reply-to: <50220216.14907471.1433901374432.JavaMail.zimbra@xxxxxxxxxx>
References: <20150609004114.GA9357@xxxxxxxxxx> <557641A2.7040801@xxxxxxxxx> <20150609020038.GB9357@xxxxxxxxxx> <5576D75E.2010205@xxxxxxxxxx> <50220216.14907471.1433901374432.JavaMail.zimbra@xxxxxxxxxx>
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On 06/09/2015 08:56 PM, Nathan Scott wrote:
> 
> 
> ----- Original Message -----
>>> pairs, where A-B traffic might appear then disappear then later
>>> reappear).  What pmdaCacheOp sequence would you recommend?
>>
> 
> Whatever sequence caused investigation of the original problem would
> do the trick.  It doesn't need to be complex, and doesn't need to hit
> all possible code paths/situations.  This sounds like something that
> could be readily automated using a custom pmdajson data source?  Or,
> whatever you used to expose the problem & test the fix by hand, can
> that be turned into a shell script?  That'd get the first part sorted
> (automated reproduction of the fundamental aspects of the problem),
> then...
> 
>>>> Also, some qa to demonstrate the issue and the fix would be
>>>> appropriate, especially at this stage of the release.
>>>
>>> The problem showed up with dramatic slowdowns and lots of diagnostic
>>> I/O traffic into /var/tmp and the pmda .log file, not as differences
>>> at the pmapi client level (other than sloth).  How would one qa that?
> 
> Once the above (even simple) reproducer exists, then the test could
> just do _pmda_filter_logfile ... if no logged error messages exist,
> the test demonstrates the fix & this slowdown can no longer happen
> (AIUI) as a result of that log() call.
> 
> This has the nice property that problems unanticipated at this stage
> (i.e. other logged errors, perhaps from a json library, perhaps from
> elsewhere in the PMDA) would be detected in the future with no change
> to the test, since they would also show up in the filtered log.
> 
>> maybe capture an archive with a lot of instances coming and going in
>> a 'wildly fluctuating' manner as above, e.g. a script that generates
>> json data from /dev/random modulo 1000000, with churn of say half
>> of them re-appearing or disappearing between fetches? Check the log
>> doesn't grow too much, and we get PM_ERR_INST when expected, etc.

I'm all for qa tests, but writing a qa test for this small bug seems
like overkill, especially since there really isn't a good way to test
it. The effort required to develop a test for this small bug vastly
outweighs the bugs importance IMHO.

-- 
David Smith
dsmith@xxxxxxxxxx
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)

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