RE: Parsing question

  • From: "Koivu, Lisa" <Lisa.Koivu@xxxxxxxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Thu, 4 Mar 2004 16:48:47 -0500

Thanks Wolfgang for your reply.  I suspected something of the sort but
the article didn't reference that. 

-----Original Message-----
From: Wolfgang Breitling [mailto:breitliw@xxxxxxxxxxxxx] 
Sent: Thursday, March 04, 2004 4:17 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Parsing question

Analyzing objects invalidates all execution plans which are dependent on

those objects ( unless you set no_invalidate=>true in oracle 9 ) forcing

the statement to go through the full parse again with the possibility of
e 
different execution plan as a result of the new statistics.

At 12:45 PM 3/4/2004, you wrote:
>Hello my learned friends,
>
>I read Bjorn Engsig's paper over a huge plate of sushi for lunch.
>Refreshing memory and opening your sinuses never hurts.  However, I
have
>a question about this statement:
>
>"During the first execute of a SQL statement, the optimization takes
>place, i.e. Oracle finds the best path to access data.  The access
plan,
>along with the SQL statement and it's parse tree is stored in the
>library cache.  Finally, the SQL statement is executed, and for
queries,
>the resulting rows are then fetched. Once a statement is parsed and
>executed, it can efficiently be executed again, completely avoiding the
>parse and optimization steps."
>
>My question is:  If a statement is stored with the execution plan, then
>if the statement is still in cache when the stats change, doesn't the
>plan change?  I deal with changing execution plans daily, and my first
>response is "how fresh are the stats".  95% of the time, an analyze
>fixes the problem and the plan changes for the exact same statement.
>
>What am I missing? Thanks everyone
>
>
>Lisa Koivu
>
>
>
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Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com 


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