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Re: pctincrease = 0 or pctincrease = 1 is better?

From: Howard J. Rogers <howardjr_at_www.com>
Date: 2000/06/17
Message-ID: <394c0ddc@news.iprimus.com.au>#1/1

"Huy Vu" <huyv_at_usa.net> wrote in message news:961124340.776256_at_news.aei.ca...
> Hi all,
>
> Our oracle database 8iv2 8.1.6 was created with pctincrease = 1. The
> result after running Oracle Expert program tell us the value of
 pctincrease
> should be changed from 1 to 0.
>
> I've never worked with pctincrease = 1 so I'm confusing now.
>
> Which value should I set for pctincrease will be better?
>
> Thanks in advance for any help.
>
> H.V
>
>

Zero every time.

A non-zero setting for PCTINCREASE causes SMON to automatically coalesce free extents (ie, create large single extents of free space where before there were multiple, small contiguous extents). Sounds like good news, except that SMON will do its stuff when *it* feels like it -which may not be quite what you want for performance reasons. Furthermore, nobody ever needs coalescing if they ensure that all segments within a given tablespace use the same size extents -since all your free extents would already be the right size for all your segments, they wouldn't need coalescing into larger ones.

Given that a non-zero setting for PCTINCREASE will actually *cause* inconsistent extent sizes, it's fairly obvious that PCTINCREASE actually causes the problem it then goes on to solve, which sounds like a bad deal to me!

If you can't ensure consistent extent sizes for your segments, then you will probably need some form of coalescing from time to time -but I strongly suggest you do the 'good DBA' thing, and arrange for coalescing to take place at a time of *your* choosing -by manually issuing the 'alter tablespace X coalesce;' command (perhaps script all tablespaces to be coalesced at a quiet time for the database, using cron or AT).

In either event, it means that PCTINCREASE should always be set to zero.

Regards
HJR
>
Received on Sat Jun 17 2000 - 00:00:00 CDT

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