Oracle-L: RE: Difference - Rebuild and Analyze index

From: <John.Hallas_at_vodafone.co.uk>
Date: Thu, 17 Oct 2002 00:33:21 -0800
Message-ID: <F001.004EBAF0.20021017003321@fatcity.com>

I think you are correct Charlie,
In 8i statistics can be collected when you are creating or altering an index. You must use compute statistics (estimate is not an option). You can rebuild an index and compute statistics, however you cannot do it using the online keyword

John

-----Original Message-----

[mailto:Charlie_Mengler_at_HomeDepot.com]
Sent: 16 October 2002 18:44
To: Multiple recipients of list ORACLE-L

At least on my DB's doing ALTER INDEX <index_name> REBUILD does in fact populate the statistics.
I discovered this by accident on one RBO DB which started giving poor performnce after doing some
REBUILDs (OPTOMIZER_MODE=CHOOSE).

                      ora ak

                      <ora_magic_at_yahoo.        To:       Multiple recipients
of list ORACLE-L <ORACLE-L_at_fatcity.com>             
                      com>                     cc:

                      Sent by:                 Subject:  Re: Difference -
Rebuild and Analyze index                              
                      root_at_fatcity.com

 

 

                      10/16/2002 08:49

                      AM

                      Please respond to

                      ORACLE-L

Yes Marul , I think there is a big differenece in them . When you are rebulding the index means you are re-organzing the entries in the index , may be removing the entries for the rows deleted in past and so forth so on. But this doesn't generate any statistics about index.

When you analyze index, you generate information ( statistics) about the data in index , like leaf blocks or depth of index etc.

None of these should require orther , but they have some effect .

Like if you rebuild index , after that you dont have latest statistics and queries may not perform upto mark .

-oramagic

Marul Mehta <marul_at_zycus.com> wrote:
Hi,

Can anybody please tell me the difference between -

SQL > execute DBMS_UTILITY.ANALYZE_SCHEMA('BLAH','COMPUTE',NULL,30,'FOR ALL INDEXES');
and
SQL > select 'ALTER INDEX ' || INDEX_NAME || ' REBUILD ONLINE;' from USER_INDEXES
If I execute any one the above do i need to execute the other also?

After how many days/hour it should be executed.

TIA,
Marul.

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