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Re: Autoallocate vs Uniform extent performance

From: Rachel Carmichael <wisernet100_at_yahoo.com>
Date: Fri, 04 Apr 2003 17:28:51 -0800
Message-ID: <F001.0057B2CB.20030404172851@fatcity.com>


Jack,

I've got no experience with out-of-line CLOB segments, so I don't know if that changes how the drop would work.

As for the maximum number of extents, that's what I was told. Not that it was necessarily "don't ever do that", just something to think about.

Rachel
--- JApplewhite_at_austin.isd.tenet.edu wrote:
> Rachel,
>
> At a recent past job, under 8.1.6 on Win2k we had tables with
> out-of-line
> CLOB segments of 30,000 extents (1MB each). Every month we dropped
> one to
> make room for another (6 months of CLOB documents online). It always
> just
> took a few seconds for the drop. These were in DMTs.
>
> Later we switched servers and I changed to LMTs of 100MB Uniform
> Extents
> for the CLOB segments. Going from 30,000 to 300 extents for those
> hulks
> made no noticeable difference in query or interMedia indexing
> performance,
> nor did it noticeably change the time it took to drop the tables.
>
> Here at AISD, our student information database (SASI, for those in
> Education who know this 3rd party app) has over 47,000 tables and
> 70,000
> indexes (typical abysmal design for a 3rd party app, eh?), many of
> them
> empty or with very few rows. A few months ago I rebuilt it under
> 8.1.7.4.6
> (Win2k - it was previously at 8.1.7.0.0) with LMTs of 8KB Uniform
> Extents
> to save space. Surprisingly, only 40 or so segments have over 1000
> extents. One, a consolidated Student table, has a little over 10,000
> extents. We've noticed no problem at all with performance, etc.
>
> I've not been concerned about extent counts for several years now,
> and I've
> seen nothing convincing that I should be. Maybe I've just not hit
> the
> situation where it matters. That is not to say that extents don't
> matter,
> but it's only if they obey the stupid directives of uninformed
> duhvelopers,
> such as those of our 3rd party Financials system, where they used
> PctIncrease of 50. Like children and dogs, there are no bad extents,
> just
> bad designers. ;-)
>
> Jack C. Applewhite
> Database Administrator
> Austin Independent School District
> Austin, Texas
> 512.414.9715 (wk)
> 512.935.5929 (pager)
> JApplewhite_at_austin.isd.tenet.edu
>
>
>
>
>
> Rachel Carmichael
>
> <wisernet100_at_yaho To: Multiple
> recipients of list ORACLE-L
> o.com>
> <ORACLE-L_at_fatcity.com>
> Sent by: cc:
>
> root_at_fatcity.com Subject: Re:
> Autoallocate vs Uniform extent performance
>
>
>
>
> 04/04/2003 07:01
>
> AM
>
> Please respond to
>
> ORACLE-L
>
>
>
>
>
>
>
>
>
> rumor hath it (as I've never actually had an object hit that high a
> number) that when you exceed 4K extents it's time to resize. This
> came
> from one of the instructors in Oracle University, one who is
> well-known
> to actually have more than a clue. He said this at the Data Internals
> class, before 9i was released.
>
> I have not seen his test results but.... I do know that tests done
> with
> DMTs have shown that large numbers of extents (I believe Kevin Loney
> tested with 60K extents, and I vaguely remember a conversation with
> Cary where he said he had also tested large numbers) are a problem
> during operations that empty a lot of extents (think large deletes)
> because of thrashing on FET$ and UET$. Since an LMT doesn't access
> those tables by design, I would think that that problem goes away.
> --
> Author: Rachel Carmichael
> INET: wisernet100_at_yahoo.com
>
>
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author:
> INET: JApplewhite_at_austin.isd.tenet.edu
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Rachel Carmichael
  INET: wisernet100_at_yahoo.com

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Received on Fri Apr 04 2003 - 19:28:51 CST

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