Re: SCSI vs SATA - Mailing list pgsql-performance

At 02:19 PM 4/6/2007, Michael Stone wrote:
>On Fri, Apr 06, 2007 at 12:41:25PM -0400, Ron wrote:
>>3.based on personal observation, case study reports, or random
>>investigations rather than systematic scientific evaluation:
>>anecdotal evidence.
>
>Here you even quote the appropriate definition before ignoring it.
>>In short, professional advice and opinions are supposed to be
>>considerably more rigorous and analytical than anything
>>"anecdotal".  The alternative is "malpractice".
>
>In any profession where malpractice is applicable, the profession
>opinion had better be backed up by research rather than anecdote.
>I'm not aware of any profession held to a "malpractice" standard
>which is based on personal observation and random investigation
>rather than formal methods.
Talk to every Professional Engineer who's passed both rounds of the
Professional Engineering Exams.  While there's a significant
improvement in quality when comparing a formal study to professional
advice, there should be an equally large improvement when comparing
professional advice to random anecdotal evidence.

If there isn't, the professional isn't worth paying for.   ...and you
=can= be successfully sued for giving bad professional advice.


>>studies.  I respect that.  Unfortunately the RW is too fast moving
>>and too messy to wait for a laboratory style study to be completed
>>before we are called on to make professional decisions on most
>>issues we face within our work
>>IME I have to serve my customers in a timely fashion that for the
>>most part prohibits me from waiting for the perfect experiment's outcome.
>
>Which is what distinguishes your field from a field such as
>engineering or medicine, and which is why waving the term
>"malpractice" around is just plain silly.

Ok, since you know I am an engineer that crossed a professional line
in terms of insult.  That finishes this conversation.

...and you know very well that the use of the term "malpractice" was
not in the legal sense but in the strict dictionary sense: "mal,
meaning bad" "practice, meaning "professional practice."   ...and
unless you've been an academic your entire career you know the time
pressures of the RW of business.


>  And claiming to have to wait for perfection is a red herring. Did
> you record the numbers of disks involved (failed & nonfailed), the
> models, the environmental conditions, the power on hours, etc.?
> That's what would distinguish anecdote from systematic study.

Yes, as a matter of fact I =do= keep such maintenance records for
operations centers I've been responsible for.  Unfortunately, that is
not nearly enough to qualify for being "objective".  Especially since
it is not often possible to keep accurate track of every one might
want to.  Even your incomplete list.
Looks like you might not have ever =done= some of the studies you tout so much.


>>Agreed.  OTOH, there's not supposed to be anything casual,
>>ill-considered, or low quality about professionals giving
>>professional opinions within their
>>fields of expertise.  Whether numbers are explicitly involved or not.
>
>If I go to an engineer and ask him how to build a strong bridge and
>he responds with something like "Well, I always use steel bridges.
>I've driven by concrete bridges that were cracked and needed
>repairs, and I would never use a concrete bridge for a professional
>purpose." he'd lose his license.  You'd expect the engineer to use,
>you know, numbers and stuff, not anecdotal observations of bridges.
>The professional opinion has to do with how to apply the numbers,
>not fundamentals like 100 year loads, material strength, etc.
..and I referenced this as the knowledge base a professional uses to
render opinions and give advice.  That's far better than anecdote,
but far worse than specific study.  The history of bridge building is
in fact a perfect example for this phenomenon.  There are a number of
good books on this topic both specific to bridges and for other
engineering projects that failed due to mistakes in extrapolation.


>What you're arguing is that your personal observations are a
>perfectly good substitute for more rigorous study,

Of course I'm not!  and IMHO you know I'm not.  Insult number
two.  Go settle down.


>and that's frankly ridiculous.

Of course it would be.  The =point=, which you seem to just refuse to
consider, is that there is a valid degree of evidence between
"anecdote" and "data from proper objective study".  There has to be
for all sorts of reasons.

As I'm sure you know, the world is not binary.


>In an immature field personal observations may be the best data
>available, but that's a weakness of the field rather than a
>desirable state. 200 years ago doctors operated the same way--I'm
>glad they abandoned that for a more rigorous approach. The
>interesting thing is, there was quite a disruption as quite a few of
>the more established doctors were really offended by the idea that
>their professional opinions would be replaced by standards of care
>based on large scale studies.
..and this is just silly.   Personal observations of trained
observers are known and proven to be better than that of random observers.
It's also a hard skill to learn, let alone master.

=That's= one of the things we technical professionals are paid for:
being trained objective observers.

...and in the specific case of medicine there are known problems with
using large scale studies to base health care standards on.
The statistically normal human does not exist in the medical sense.
For instance, a given woman is actually very =unlikely= to have a
pregnancy exactly 9 months long.  Especially if her genetic family
history is biased towards bearing earlier or later than exactly 9 months.
Drug dosing is another good example, etc etc.

The problem with the doctors you mention is that they were
=supposedly= objective, but turned out not to be.
Similar example from Anthropology can be found on Stephen Jay Gould's
_The Mis-measure of Man_


Have a good day.
Ron Peacetree