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What do Oracle waits mean [message #332161] Mon, 07 July 2008 13:26 Go to next message
lunaut
Messages: 6
Registered: July 2008
Junior Member
I am a bit confused with definition Oracle waits. For instance, OEM or other Oracle tools indicate that a session has a long wait. There could be 3 cases
1) it is waiting for resources used by other session, more like a blocking
2) waiting for Oracle complete the job for it, like loading data blocks (disk io)
3) combination of the above 2.

In this case how to tune the query. For case 1, we should tune the blocking session, and we can identify the blocking session in v$session. For 2, this very query need to be tune.

The confusion is if a session waits for a long time and no blocking session is found, does it mean that this query causes much the overheads. In other words, we can identify the heavy queries for tuning by the longest nonblocking waits.

Thanks
Re: What do Oracle waits mean [message #332162 is a reply to message #332161] Mon, 07 July 2008 13:29 Go to previous messageGo to next message
BlackSwan
Messages: 25050
Registered: January 2009
Location: SoCal
Senior Member
http://www.orafaq.com/forum/t/88153/0/
Please read & follow posting guidelines as stated in URL above
Re: What do Oracle waits mean [message #332172 is a reply to message #332161] Mon, 07 July 2008 14:17 Go to previous message
Michel Cadot
Messages: 64152
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
You can have a look at Database Performance Tuning Guide, there is a description of wait events.

Regards
Michel
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