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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