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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Why a rebuild speeds up my queries.
David
In addition to Richard's comments: Between before and after rebuilds, table scans(short tables) have gone up from 783 to 3285, whereas table fetch by rowid has gone down from 4.4M to 3.9M. Table scan rows gotten also has gone up from 9M to 39M. I think, your process, after the table rebuild is scanning at least one smaller table using FTS too. I guess, only 10046 event trace will identify this correctly. BTW, are these SQLs use bind variables or are they literal variables ?
PS: Not sure, how you are looking at the explain plan, but in few cases, sqlplus autotrace and sqltrace explain plans do not match.
Thanks
Riyaj "Re-yas" Shamsudeen
Certified Oracle DBA
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of David Sharples
Sent: Wednesday, September 01, 2004 7:48 AM
To: oracle-l_at_freelists.org
Subject: RE: Why a rebuild speeds up my queries.
Hi Richard thanks for the snippet about dbms_stats, yes we do use that. Next time I will use analyze and see what that is.
As for pctfree, the tables are set to the default of 10. I think this is the problem because the rows start of as 'skinny' ones with all values being 0, then they get updated constantly with true values, numbers up to 10 digits, varchar2 up to 20, so they then become fat and must migrate.
Do you know of a good link where it tells me how to set pctfree properly?
Oracle docs are good but I find them to tell me more what it is about that what it should be.
Thanks very much
Dave
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Richard Foote
Sent: 01 September 2004 13:22
To: oracle-l_at_freelists.org
Subject: Re: Why a rebuild speeds up my queries.
Hi David,
Your "table fetch continued row" count has certainly plummeted so something's changed there.
When you say dba_tables shows nothing, you don't by any chance use dbms_stats to analyze as chain_cnt is only calculated with the "old" analyze command (else you just get a 0).
In which case, yes, your pctfree is buggered.
Just a thought.
Cheers
Richard
----- Original Message -----
From: "David Sharples" <dsharples_at_cerebrussolutions.com>
To: <oracle-l_at_freelists.org>
Sent: Wednesday, September 01, 2004 9:21 PM
Subject: Why a rebuild speeds up my queries.
Hi,
I have a process that overtime slowly gets slower and slower (execution
plans are the same)
A rebuild of the table / index fixes this and makes it go quick again. I know that we shouldn't need to rebuild things, so I need to know what is wrong in my setup which is causing this.
The setup is this: oracle 9.2.0.4 on Solaris
Running queries against hashed partitioned table which never get deleted them, they only get inserted into and then updated a fair amount.
We think it is due to row migration / chained rows but chain count from dba_tables showed nothing after an analyze.
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