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Re: move table for chianed rows?

From: Andrea <netsecurity_at_tiscali.it>
Date: 27 Mar 2007 00:42:12 -0700
Message-ID: <1174981332.546918.324720@b75g2000hsg.googlegroups.com>


On 26 Mar, 16:25, "Mark D Powell" <Mark.Pow..._at_eds.com> wrote:
> On Mar 26, 7:11 am, "Andrea" <netsecur..._at_tiscali.it> wrote:
>
> > Hi,
>
> > sorry for my question (i'm a newbie DBA) but i've read on forums that
> > for resolve chained rows on tables, it is enough move table in this
> > method:
>
> > alter table FOO move;
>
> > is true? but what does it do exactly this command??
>
> > thanks for any support!
>
> > bye
> > andrew
>
> Actually a chained row is a row to big to fit into a single Oracle
> block and as such rebuilding the table will not eliminate chained
> rows.
>
> Unfortunately Oracle places the count of migrated rows in the
> dba_tables.chain.cnt column. A migrated row is a row that after an
> update operation would no longer fit back into the block it was in so
> Oracle migrates the row to a new block leaving a rowid marker behind
> that points to the new row location. Accesses via an index go to the
> old location and then have to do an extra IO to find the row in its
> new location.
>
> Before rebuilding a table to eliminate chained rows you need to look
> at the average row length and make sure it is less than the available
> space within a block. Otherwise you would be wasting your time.
>

ok, so.. if i understand...
for eliminate chained rows i have to:

  1. Estimate avg row length through dbms_stats.gather_tables or analyze
  2. Edit the storage of table (pctfree)
  3. alter table FOO move;

is right?

and you advise to use ASM ?

thanks very much! Received on Tue Mar 27 2007 - 02:42:12 CDT

Original text of this message

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