Should you still tune queries by LIOs?

  • From: ryan_gaffuri@xxxxxxxxxxx
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Tue, 07 Sep 2004 13:24:40 +0000

I believe its Mogens chapter in the Tales of the Oak Table book where he said 
he found with 10g that LIOs and CPU usage do not necessarily correspend. He 
argues that tuning queries should be explicitly based on elapsed time.
My understanding of LIOs is that every LIO is a buffer cache latch get, so even 
if you do not use up more CPU you are incurring serialization and under 
concurrency can cause performance problems. I have seen queries go from 20,000 
LIOs down to 300 with a very small performance improvement. Is it worth it to 
spend the time to do this? 
BTW, its a very good book. The chapter by Dave Ensor on the history of Oracle 
is one of the best chapters you can find anywhere. I hope he writes more now 
that he is retired. 
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