Re: online index rebuilds

Hi,

Thinking about why full table scan is required for online index rebuild... 
Maybe the potential index block splits are the reason why index FFS can't be 
used for online index rebuild? Consistent reads should overcome this issue 
though, but maybe there is something we don't know...

Btw, with offline index rebuild the decision whether to go with FTS or index 
FFS is also cost based (at least 10.2). If I have only single-column table 
indexed then the offline rebuild may do an FTS instead of fasf full index scan. 
(also, even in the case of fast full index scan, rows have to be sorted anyway, 
because index fast full scan doesn't guarantee an ordered result).

Tanel.
  ----- Original Message ----- 
  From: Roger Xu 
  To: joseph@xxxxxxxxxxxxxx ; Bobak, Mark ; ORACLE-L 
  Cc: tanel.poder.003@xxxxxxx 
  Sent: Wednesday, January 25, 2006 2:05 PM
  Subject: online index rebuilds


  Any other differences besides: 1) does not lock the table; 2) does a full 
table scan instead of full index scan; ?
    -----Original Message-----
    From: oracle-l-bounce@xxxxxxxxxxxxx 
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Joseph Amalraj
    Sent: Tuesday, January 24, 2006 9:48 AM
    To: Bobak, Mark; joseph@xxxxxxxxxxxxxx; ORACLE-L
    Subject: RE: ORA-01652: unable to extend temp segment


    Thanks, 

    Had read the article, but I am interested as to why Oracle is doing a full 
table scan instead of full index scan for online index rebuilds.

    "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxxxxx> wrote:
      Well, my name is not Tanel, but I'll jump in here and point you to 
MetaLink Doc ID 272762.1.


      -Mark
      -- 
      Mark J. Bobak 
      Senior Oracle Architect 
      ProQuest Information & Learning 
      "There are 10 types of people in the world:  Those who understand binary, 
and those who don't." 




--------------------------------------------------------------------------
      From: oracle-l-bounce@xxxxxxxxxxxxx 
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Joseph Amalraj
      Sent: Tuesday, January 24, 2006 9:59 AM
      To: ORACLE-L
      Subject: Re: ORA-01652: unable to extend temp segment


      Thanks Tanel, 

      Is there any reason why Oracle does full table scans for online rebuilds 
and not for offline.

      Regards

      Joseph Amalraj

      Tanel Põder <tanel.poder.003@xxxxxxx> wrote:
        Online rebuilds don't use existing index for creating new. They do full 
table scan on the table.

        However, in both cases, old index segment is kept until new one is 
ready to use and switch to it is done. Also the journal IOTs used for online 
rebuilds are stored in the target tablespace, so if you've got lots of 
transaction s going on while you are rebuilding the index onl ine, you need 
additional space in target tablespace.

        Tanel.

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