Whilst I agree with Steve's assessment as it applies
to squeezing the n'th degree of efficiency from
Oracle, I'd be keen on hearing from anyone that
suffered any detectable / noticeable performance
degradation from having an excess of extent map blocks
in their system.
Don't get me wrong, I've no doubt that such a
degradation must exist, but I'd be very surprised if
there are many databases out there that are that well
optimized so that this becomes a relevant issue.
If that's the case, then I'm back to my argument that
for almost all databases, you can quite happily get
away with a 1m extent size for *every* segment in the
database (assuming a 4G ceiling on segment size)
Cheers
Connor
- Jacques Kilchoer <Jacques.Kilchoer_at_quest.com>
wrote: > A possible justification for using autoextend
was
> mentioned on the list
> recently.
>
> You have a table whose growth you cannot predict.
> Put it in an autoextend
> tablespace so that you won't end up with an unwieldy
> number of extents.
> Though of course people have shown recently on the
> list that in a locally
> managed tablespace, dropping a table with a very
> large number of extents
> (which was one of my objections to a very large
> number of extents) doesn't
> seem to take very long. But Steve Adams does mention
> in his "planning
> extents" article (
> http://www.ixora.com.au/tips/creation/extents.htm )
> : "we
> recommend that the number of extents per segment in
> locally managed
> tablespaces be limited to the number of rows that
> can be accommodated in the
> extent map within the segment header block - that
> is, approximately
> (db_block_size / 16) - 7."
>
> Another reason - one of the software products that I
> help develop asks the
> user to select a tablespace to install a repository
> of objects needed by our
> product. Some of those objects will be very small,
> and some have the
> potential of becoming very large. I don't want to
> have to ask the user to
> choose 2 or 3 different tablespaces at install time.
> So an autoallocate
> tablespace would be a good solution.
>
>
>
> > -----Original Message-----
> > From: Jared.Still_at_radisys.com
> [mailto:Jared.Still_at_radisys.com]
> >
> > Tom is a very bright guy.
> >
> > Can't say I always agree with him though. This is
> > one of those instances.
> >
> > In this article he refers to 335 extents being
> 'well within the
> > bounds of reason'. There are other places where
> he
> > states that the number of extents doesn't matter.
> >
> > Are there any good reasons for using autoallocate?
>
Connor McDonald
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Received on Wed Apr 16 2003 - 00:43:39 CDT
