RE: oracle docs do say # of extents effect performance

From: Richard Ji <Richard.Ji_at_ztango.com>
Date: Fri, 20 Jun 2003 10:20:12 -0700
Message-ID: <F001.005B6692.20030620100010@fatcity.com>

Even without stripping you can't gaurantee it will be a contiguous section of disk space. The file could be scattered across the file system.

Richard Ji

-----Original Message-----
Sent: Friday, June 20, 2003 1:12 PM
To: Multiple recipients of list ORACLE-L

My favorite part is
"and all of the table's data will be stored in a relatively contiguous section of disk space".

Is this even reasonable to believe, especially with any kind of striping implemented?

>>> [EMAIL PROTECTED] 06/20/03 12:00PM >>>
Two reasons:

if you go into extent map blocks then you will suffer an overhead of at least 1 billionth of a percent :-)
more seriously, its generally easier to pick up a "rogue" table if its run into thousands of extents and you had not intended it to. Its not a performance problem per se, but its indicative that its a segment thats doing something that was unforseen in the design phase..

hth
connor

[EMAIL PROTECTED] wrote: > I just read a .pdf by a couple of people at oracle
> called Stop Fragmenting and start living where it
> says not worry about the number of extents in a
> tablespace. However in the administrators doc it
> says the following:
>
> Estimate Table Size and Set Storage Parameters
> Estimating the sizes of tables before creating them
> is useful for the following reasons:
>
> You can use the combined estimated size of tables,
> along with estimates for indexes, rollback segments,
> and redo log files, to determine the amount of disk
> space that is required to hold an intended database.
> From these estimates, you can make correct hardware
> purchases and other decisions.
>
> You can use the estimated size of an individual
> table to better manage the disk space that the table
> will use. When a table is created, you can set
> appropriate storage parameters and improve I/O
> performance of applications that use the table. For
> example, assume that you estimate the maximum size
> of a table before creating it. If you then set the
> storage parameters when you create the table, fewer
> extents will be allocated for the table's data
> segment, and all of the table's data will be stored
> in a relatively contiguous section of disk space.
> This decreases the time necessary for disk I/O
> operations involving this table.
>
> this is at the following link:
>
>
http://download-west.oracle.com/docs/cd/A87860_01/doc/server.817/a76956/tables.htm#208

>
> am I reading this wrong or is Oracle stating that
> you should have less extents in a table? I know
> several people on here have posted that the number
> of extents used by an object is almost irrelevant.
>
> --
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> Author: <[EMAIL PROTECTED]
> INET: [EMAIL PROTECTED]
>
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Received on Fri Jun 20 2003 - 12:20:12 CDT