Mark,
Appology accepted ;-)
Some people flame me because they did not read my post
carefully. I said that for optimal performance the
number of extents with an 8K blocksize was 505. People
thought that was a maximum.
2147483645 is a theoritical limit. It's like the
maximum Oracle database size : 512 Petabytes .
If everything was simple , they're would be less job
for the dba.
By putting a so large limit, you are sure that the
system won't stopped. I'd rather have 2001 extents and
not having the users complaining that the system
stopped.
- Mark Leith <mark_at_cool-tools.co.uk> a écrit : > Hi
List,
>
> I have been reading through the 8i Tuning &
> Performance Guide, and
> remembered a topic on the list a few weeks back
> discussing the maximum
> number of extents for a LMT.
>
> In the Tuning I/O section of this guide there is a
> reference to this
> stating:
>
> ---snip---
> Evaluating Unlimited Extents
>
> Even though an object may have unlimited extents,
> this does not mean that
> having
> a large number of small extents is acceptable. For
> optimal performance you
> may
> decide to reduce the number of extents.
>
> Extent maps list all extents for a particular
> segment. The number of extents
> entries
> per Oracle block depends on operating system block
> size and platform.
> Although
> an extent is a data structure inside Oracle, the
> size of this data structure
> depends on
> the platform. Accordingly, this affects the number
> of extents Oracle can
> store in a
> single operating system block. Typically, this value
> is as follows:
>
> Block Size (KB) Maximum Number of Extents
> 2 121
> 4 255
> 8 504
> 16 1032
> 32 2070
>
>
> For optimal performance, you should be able to read
> the extent map with a
> single
> I/O. Performance degrades if multiple I/Os are
> necessary for a full table
> scan to get
> the extent map.
>
> Avoid dynamic extension in dictionary-mapped
> tablespaces. For
> dictionary-mapped tablespaces, do not let the number
> of extents exceed
> 1,000. If extent allocation is local, then do not
> have more than 2,000
> extents. Having too many extents reduces performance
> when dropping or
> truncating tables.
> ---snip---
>
> Now, I also remember somebody stating that
> MAXEXTENTS should be set to 504
> for an 8K block size, and he was flamed.. I also
> added to this, and now
> appologise..
>
> Now, the question arises :
>
> I created an LMT with the default storage
> parameters, and Oracle in its
> infinite wisdom, gave a MAXEXTENTS value of
> 2147483645!!
>
> A few more than 2000, was Larry thinking of his bank
> balance when he decided
> on this? :)
>
> You know, it's so great that they put these little
> "pearls" of wisdom in to
> tuning guides, that you have to dig in to, just to
> find a ghost of an
> answer, but when it comes to putting them as
> standard in to the bloody
> product they give stupid values that would grind a
> system to a halt if ever
> allowed to happen!! Would it not then make sense to
> just set this as a
> default??
>
> Am I being naive? LOL..
>
> Can we all join hands and shout "Thank you
> LARRY!!!!"
>
> Mark
>
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Stephane Paquette
DBA Oracle
stephane_paquette_at_yahoo.com
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Received on Thu Feb 15 2001 - 11:49:19 CST
