Re: questions regarding nologging

Mladen,
Thanks for your input. Yes, I also rebuilt all relevant indexes with nologging option so no normal redo genearation either. However, the table was moved into LMT tbs from a dictionery managed tbs.

Regards
Rafiq

Reply-To: ORACLE-L_at_fatcity.com
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: Wed, 22 Oct 2003 21:39:25 -0800

Well, Rafiq, when you move the table, indexes are marked stale, which means that you must rebuild them. Marking indexes unusable shouldn't generate any redo log, except for the dictionary block that was altered. Other then that,   moving table is an opration roughly analogous to CTAS and I suspect that if the target table is NOLOGGING, that the whole operation is done in the "direct" fashion, with block prebuild and appended below the high watermark. I tried it and I didn't see any redo log generation either. That is probably the reason why splitting partitions also doesn't generate redo, as Arup has noted. Oracle has highly optimized many of these operations and avoding
excessive redo log generarion is one of the best optimizations one can make.

On 2003.10.22 23:54, M Rafiq wrote:
>Waleed,
>I agree with you as I moved a 5GB table last week with nologging option
>with extent size 500M and did not see any normal redo generation for that.
>It is 8.1.7.0 database. that table has 8 indexes for total size of almost
>3GB.
>
>Regards
>Rafiq
>
>
>
>
>Reply-To: ORACLE-L_at_fatcity.com
>To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
>Date: Wed, 22 Oct 2003 17:14:24 -0800
>
>Alter table ...Move TS nologging....
>is 100% equivalent to CTAS and should generate minimal amount of logging
>even if it ran serially (no PQ).
>
>Actually the type of command is considered "CREATE TABLE"
>
>So I'm not sure how the original poster was able to determine that the
>operation generated huge redo logs!
>
>This could be possible if the redo logs has to do with Extents management
>and the needed RBS to manage it (specially if the extents are very small
>and
>the TS is dictionary based).
>
>Waleed
>
>-----Original Message-----
>Sent: Wednesday, October 22, 2003 4:54 PM
>To: Multiple recipients of list ORACLE-L
>
>
>That's because nologging attribute only affects the "direct"
>operations, i.e. the the operations that prebuild blocks and add
>them below the flood watermark. That includes sqlloader with direct=y,
>inserts with /*+ append */ hint and CTAS. Normal SQL based operations
>are not affected.
>
>On 10/22/2003 04:39:34 PM, Roger Xu wrote:
> > > Hi Gurus,
> > >
> > > I have a couple of questions regarding "nologging".
> > >
> > > 1) alter table tabname move tablespace tbsname nologging;
> > >
> > > How come this sql still generated same amount of redo logs equal
> > to the size of the table?
> > >
> > > 2) alter index idxname rebuild tablespace tbsname nologging;
> > >
> > > This sql only generate minimum redo logs.
> > > But the index ends up LOGGING=NO in dba_indexes view.
> > > How do I turn the logging on for this index?
> > >
> > > Thanks,
> > >
> > > Roger Xu
> > > Database Administrator
> > > Dr Pepper Bottling Company of Texas
> > > (972)721-8337
> > >
> > --
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
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>Mladen Gogala
>Oracle DBA
>
>
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Author: M Rafiq
  INET: rafiq9857_at_hotmail.com

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