Re: Size of Extents

Tracie Thomas wrote:
>
> Srinivasa Rao Vaikuntam wrote:
> >
> > Hi
> >
> > I am trying to figure out a way to estimate the size of the initial
> > extent and next extent for a given table. On what factors does this
> > depend? Does oracle allocate extents in any fixed block sizes? I have
> > seen some code, where it is specified for most of the tables, the
> > initial extent is 56k (in some cases 126 k), and the next extent being
> > 56k.
> >
> > Is this documented anywhere?
> >
> > We are running Oracle 7.2 on a HP-UX 10.0.
> >
> > thanks in advance
> > srini

Hi!

When you want to estimate "initial" and "next" extents pay attention to the following:

• To increase the performance of your database a table should allocate only ONE extent!
• If you allocate more than 10 extents for one table the performance is going down.

For example:
table "drawings" constis of the following attributes:

Drawing Number: char (20)
Version       : char (2)
Revision      : char (2)
State         : char (15)

You want to store 30.000 rows in this table.

Now you can estimate:
20+2+2+15=39
39*30.000=1170000 bytes = 1.1 MB

So your initial extent should be 1.1 MB or greater.

The size of the "next" extent depends on in which way the number of the rows in this table will increase.
BE CAREFULL: On HP-UX you can normaly have only max. 121 extents!!! (this depends on the db_block_size!).

In addition to this think about "PCTINCREASE". I suggest to set PCTINCREASE = 0!

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