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RE: Spotting the real cause of a Production slowdown (10g)

From: Schultz, Charles <>
Date: Thu, 20 Apr 2006 08:52:33 -0500
Message-ID: <>

Thanks. Yes, I agree with what you are saying. One of the fallouts from our case with Oracle Support is that we are bumping up against a bug whereby the 10g SGA auto-sizer will inflate the shared pool indiscriminately, even if you are flooding it with literal statements (counter-intuitive, as you pointed out below).  

The problem with finding many copies of sql statements that look similar is how granular do you go? The common method is to substring sql_text from v$sql. How many characters do you use? To be empirical, one would have to loop through all reasonable numbers (ie, between 7 and 150). Unless you know something I don't, which is entirely possible. *grin*  

Good point about which processes are consuming CPU - I did not even think about that. How does one use the Historical view of EM to determine that information? All I can find is "CPU used" under performance, and if I try to break it down, I get user processes. But I will keep looking.  

Just saw the note from Paul Baumgartel - thanks. I will experiment with the plan_hash_value.

[] On Behalf Of Dennis Williams Sent: Thursday, April 20, 2006 8:44 AM
To: Schultz, Charles
Subject: Re: Spotting the real cause of a Production slowdown (10g)


I have seen similar problems in earlier versions of Oracle - many literal statements and a large shared pool. Think about it -- when a new SQL statement is received, Oracle must check to see if it has ever received that statement before. The larger the shared pool, the more area it must scan. Of course, it doesn't find a match, so it must parse the new statement. Then it must find a spot in the shared pool to place the newly parsed statement. Which means it must age something out. And if the application is hammering Oracle with these statements inside a loop, it gets challenging for Oracle to keep up. If this is the situation, the answer is not to increase the size of the shared pool, because that just aggravates the problem.

    Rather than looking for the single statement that is getting issued the most, you may want to look a lot of statements that are issued once but look very similar, like

           select col1 from employee where empno = 1;
           select col2 from employee where empno = 2;
In our case, the solution was to get the developers to recode the worst offenders to bind variables.

     Also, you didn't mention which Oracle processes were consuming so much CPU.  

Dennis Williams  

Received on Thu Apr 20 2006 - 08:52:33 CDT

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