On Apr 18, 4:01=A0pm, yf...@[EMAIL PROTECTED]
(Malcolm Dew-Jones)
wrote:
> joel garry (joel-ga...@[EMAIL PROTECTED]
) wrote:
>
> : On Apr 18, 2:29=3DA0am, Andreas Mosmann
<mosm...@[EMAIL PROTECTED]
group.org> wrote:
>
> : > Thank both of you,
> : >
> : > I will try it out.
> : > Is there also a way to determine what index is still needed/useful
for=
a
> : > special query?
> : >
> : > Andreas Mosmann
> : >
> : > --
> : > wenn email, dann AndreasMosmann <bei> web <punkt> de
>
> : I do believe that is the downside of deleting indices based on usage.
> : It only shows what's been used during the observation. =A0That implies
a=
> : bad assumption that the usage is completely stable. =A0To me, this
seems=
> : worse than just dropping an index and seeing who screams, since when
> : there is a problem in the future, you have to go through an entire
> : performance tuning workup because the linkage to the act of dropping
> : the index is obscured. =A0Maybe I'm missing the concept. =A0What about
a=
n
> : index that would be used when you pass some tipping point or boundary
> : condition or upgrade or change a session parameter?
>
> You can disable an index. =A0That way the definition exists but the
index =
is
> never used or maintained (i.e. no overhead). =A0If you decide it is
needed=
> you simply enable it.
But that's my point. The decision is being made on past performance,
why would you decide it is needed? Certiainlly if you are using
method-r the users would be complaining about it far too late, it
could have been needed for years between the time it was dropped and
the time a complaint is made - people tend to think "that's how the
system works" and not complain if something gets slower slowly. I
still don't see what synapses would have to be fired (thanks for that
one, Dan!) to make this tool useful. In my experience, either the
system has been well-vetted over time (like an enterprise system sold
to many customers), or it's newly developed and the thought have been
tested and decisions made (or, it's just a crappy system). It ought
to be useful for the enterprise, as vendors can't know what parts of
the system the customer will use, but I haven't seen much of that, as
a DBA I've only seen missing indices, and sometimes it takes quite a
bit of work to figure that out. Has anybody actually found this tool
useful? (not a rhetorical question, I'm curious, and always wondering
about it when I see some new feature trumpeted everywhere, but not
success stories. Of course, I don't see everything.).
Since it does take work to figure missing indices out, I can't help
but wonder if this tool is counterproductive, by making it too quick
on the draw to delete indices, making more work later. If you have to
make a big project out of it with dbms_stats, with no one complaining
about performance... in a complicated enterprise system, you may not
know how the future data growth will be impacted by business changes
and software upgrades.
>
> "when you pass some tipping point"
>
> If an index is enabled then presumably it will only be used when the CBO
> decides it is useful for a query.
Again, that's my point. The decision is being made before the CBO can
decide that.
jg
--
@[EMAIL PROTECTED]
is bogus.
=93It was them saying, 'We need to stick our hands up your back and move
your mouth for you.' =94 - Robert Bevelacqua, retired Army Green Beret
and former Fox News analyst.
http://www.signonsandiego.com/uniontrib/20080420/news_1n20mil.html
|
