Re: question on EXPLAIN

From: Mohammad Rafiq <rafiq9857_at_hotmail.com>
Date: Wed, 06 Feb 2002 14:18:20 -0800
Message-ID: <F001.0040815D.20020206141833@fatcity.com>

Try to reduce High Water Mark on your table by creating as select a backup table
truncate original table
insert into original table from backup table...

This is based on your info for full table scan...Please also rebuild indexes on that table and analyze table if you are on COST BASED..

HTH,
Regards
Rafiq

Reply-To: ORACLE-L_at_fatcity.com
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: Wed, 06 Feb 2002 13:45:44 -0800

Hi, Bill

You are right, there is really something to do with the index. I drop&re-created that PK index, it became much faster, but after 5 minutes, it became slow again, and I am sure no records insert/delete/update happened. I drop&re-created that indexes again, nothing happened this time, it is still slow!
It is really weird!

And I found on the bad performance database, a simplest query: select count(*) from table_name will take 4 seconds! the explain_plan said it used cost-optimizer, using fast_full_index_scan on that PK index,
what should I do with the index? I already tried to re-created the PK index.

The bad performance database is on a super-box, 4 CPUs and more memory. the good performance one is on a normal box. And the table and index is analyzed at same way.

thanks a lot for your reply.

Kevin Wang

Original Message ----- From: Bill Zakrzewski To: kevin wang Sent: Wednesday, February 06, 2002 12:38 PM Subject: Re: question on EXPLAIN_PLAN

Kevin,

Have these indexes been rebuilt recently? If not, you may want to consider rebuilding the indexes. Not sure if this is your issue, but if you have inserted/deleted records from your tables over time, the index levels may have grown as well.

   Bill Zakrzewski
   Senior Consultant
   Intactus Technology, Inc.

Original Message ----- From: kevin wang To: LazyDBA.com Discussion Sent: Wednesday, February 06, 2002 2:43 PM Subject: question on EXPLAIN_PLAN

Hi, guys

The problem belows is really make me confused and gave me big trouble, is there someone can give me some hlep?

I have two databses, same version(oracle 8.1.6),same O/S(win2000), same schema structure, different data(but small difference of size).

       and even exactly same explain_plan of my sql query.
       But on one database, the cardinality of one PK index access upon one 
table is 27(cost=2,card=27,bytes=756) (table rows 263758)
       and the other is 11706!!!! (cost=3,card=11706,bytes=199002)( table 
rows 351173).
       so, on one DB the sql query took 300ms, one the other, it took 5

seconds!

Any advise is highly appreciated.

thanks,

       Kevin Wang
       Database Administrator
       Vivonet Canada Inc.

MOHAMMAD RAFIQ

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Author: Mohammad Rafiq
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Re: question on EXPLAIN_PLAN