RE: Hot index block split on a very busy table--what is the impact

If the load spike is very short - so short that you cannot catch the actual wait event, I'm curious as to why this is perceived as an incident and problem to be solved.  

How long a period of "during that time nothing can be done" are we talking about?  

If you are *not* getting a waits on Index Block Split during that period, then that is probably *not* your problem, so allowing the knowledge that that you have a busy index distract you from finding what you are waiting for is probably not the best pursuit. Likewise, I would not search for all waits that generate a CPU spike, but rather try to discover what you are actually waiting for. Spinning like crazy for any latch wait by many sessions will generate a CPU spike.  

So pursue the real lead you have: waiting for latch free on cache buffer chains.  

Good luck!  

mwf  

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Zhu,Chao
Sent: Wednesday, August 30, 2006 9:53 AM To: oracle-l_at_freelists.org
Subject: Hot index block split on a very busy table--what is the impact  

hi, all,

    We have a few database with very high concurrent access busy tables, that some indexes of the busy tables could be accessed 1.5K-4K times per second. (PK lookup)

    I am wondering , when such index got block split (at the root, or branch level), what will be the impact on the system.

    Index block split is said to be an expensive operation, during the block split on branch/root block, what the other sessions that is doing select based on this index, be waiting on? There is a wait event named: Index Block Split with p1,p2,p3 pointing to block address, level.

   Document "Description of oracle 7 Wait event and enqueue" says it will yield CPU.

   We have a few production incident when load suddenly jump from 10, to several hundred, and during that time nothing can be done. From our monitoring tools, it is mainly "latch free" contention inside oracle, and it is cache buffer chains. The load spike matches the oracle description of block split, but the wait event does not match. And because the load spike time is very short, we can't capture the actual wait event/p1,p2,p3 during the exact time of the load spike time.
  Anyone have similar problem/insight into this issue?   Is there some v$ view to track, (v$segstat does not) have log about which index go through how many time block split? Or any other effecitve way?    

--

Regards
Zhu Chao
www.cnoug.org

--

http://www.freelists.org/webpage/oracle-l Received on Wed Aug 30 2006 - 10:02:33 CDT