Re: how many LIOs is too many

Most of us have probably seen some SQL at a point in time that has much worse LIO than this ... some of us much much worse.  There is no magic formula on when to attack problematic sql it depends on so many factors.

If you asked me if I have seen SQL that at times goes into the hundred thousands LIO per execution I would have to say "mumble mumble" ...     

 

________________________________
 From: Ram Raman <veeeraman_at_gmail.com>
To: ORACLE-L <oracle-l_at_freelists.org> 
Sent: Monday, January 20, 2014 6:31 PM
Subject: how many LIOs is too many
  


List, 
   
We have a SQL that is being executed few thousand times in an hour. The SQL belongs to an application supplied by a 3rd party vendor. The SQL accesses 500 rows from a million row table every time it executes, using idx range scan. This is spiking up the resource usage consistently.  (Do not know why an application would need 500 rows constantly, it uses rownum to filter out top 500 rows after order by asc).  
   
As of now this is the stats: 
   
SQL_ID           FETCHES EXECUTIONS DISK_READS BUFFER_GETS    CPU_SEC ELAPSEDSEC FIRST_LOAD_TIME
------------- ---------- ---------- ---------- ----------- ---------- ---------- -----------------------
037xx0tb72t5r     789387     789388         80  1998534791 1719853.25 1820107.77 2013-12-18/08:06:26
   
The LIO per exec was at ~1600 yesterday, it has gone to 2500 today.  
   
I have couple of questions 
   
1) Has anyone in this list worked on an app that does repeated executions of a sql retrieving so many rows.  
2) Is there any formula to calculate the number of LIOs for a SQL when it is time to say the sql is doing too many LIOs per exec. 

v11.2  
TIA,  
Ram. 

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