RE: Query on Number of Parses and Executions(for Selects from Views)

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Tue, 6 Apr 2004 01:53:43 -0500
Message-ID: <006101c41ba3$e9b99790$6f01a8c0@CVMLAP02>

Sriram,

How many parse *calls* get made is determined entirely by the application. The application is simply telling the database to parse the same statement 2,079 times. The Oracle kernel is smart enough to know that only the first requires a "hard parse," but once the app tells the db to execute a parse call, the db counts it as a parse call. ...And it costs a lot of end-user response time to process all these parse calls: lots of CPU and lots of network latency that shows up as time spent in "SQL*Net message from client" timed events.

To fix the problem, pull the parse call outside of whatever loop it's in within the application source code. If it's PL/SQL, then use the DBMS_SQL package to extract the parse call from the loop so that you have this:

  /* good */
  dbms_system.parse(...)
  loop
    dbms_sql.execute_and_fetch(...)
  end

...And NOT this:

  /* bad */
  loop
    execute immediate ...
  end

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
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-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of k.sriramkumar_at_iflexsolutions.com
Sent: Tuesday, April 06, 2004 1:23 AM
To: oracle-l_at_freelists.org
Subject: Query on Number of Parses and Executions(for Selects from Views)

Hi Guru's

I have a query like this

  select <column_name list>,rowid
  from <view>
  where col1=:b1 and col2 =:b2 and col3='N'   order by col5

This SQL is executed from PL/SQL and the query static in nature
Oracle version is 9.2.0.4
This query would be executed say 2000 times for various values of col1,col2
I traced the session and tkprof output shows that number of parses and executes are 2079.

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ----------

Parse 2079 216.92 233.07 0 0 0 0
Execute 2079 0.33 0.43 0 0 0 0
Fetch 5297 1.54 2.71 233 11929 0 3218
------- ------ -------- ---------- ---------- ---------- ----------

total 9455 218.79 236.21 233 11929 0 3218

I expected that this statement to be parsed once and executed 2079 times. why is it getting parsed 2079 times?.

Also,

Misses in library cache during parse: 1

which means that the statement was not found in the library cache only once...

My initial guess was that the optimizer was rewriting the query but checked query_rewrite_enabled=false...The optimizer mode is RULE...would not be able to change the optimizer_mode for now

Would be great if you could throw some light on this please.

Best Regards

Sriram Kumar

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Received on Tue Apr 06 2004 - 01:50:17 CDT