Database News You Can Use
A monthly newsletter for Oracle users
It’s time again for another OracleWorld conference. This year’s conference takes place in San Francisco September 7-11, and Oracle Corp. will introduce its new flagship database with Grid Computing- Oracle10G. The conference offers over 300 sessions for IT Managers, DBAs, Developers, and Oracle Partners. Focus areas include topics such as: Ask DB Specialists: Null Events
For more details, registration, and up-to-the-minute information, check out http://www.oracle.com/oracleworld/sanfrancisco/conference/.
You’re invited to submit your Oracle-related questions to us at email@example.com. Include your name, telephone number and problem description. If your question gets published, you’ll receive a free copy of our reference poster on Oracle Wait Events. So, stay tuned for future issues of The Specialist! TheServerSide.com – Developer Resources
This month’s question comes from Jonathan G. in London: When I query the Oracle wait event views, I sometimes see a wait event called “null event.” What kind of wait event is this?
Chris Lawson of the Database Specialists team responds: In Oracle 9i, it is common for an event to be titled “null event.” No, this doesn’t mean that Oracle is waiting on “nothing.” Instead, this simply means that the Oracle programmers goofed—they forgot to put the title on some events. So, if your session is waiting on disk I/O, instead of seeing the wait event called “db file scattered read,” you might see a “null event.”
Fortunately, we have some extra information that can help unravel the puzzle. Remember that most wait events have three parameters, called P1, P2, and P3. Although the “mystery” event is not named properly, the P1-P3 parameters appear to still be correct. The exact value of these parameters can give you clues on what the event could be.
For instance, the P1 and P2 parameters for a multi-block read refer respectively to the File# and Block_Id for the object being read from disk. Therefore, if the P1 and P2 parameters for a given null event happen to correlate with an actual File# and Block_Id of a table that you are accessing, it is likely that the null event is really a disk-read event. (Use the Dba_Extents view to look up File# and Block_Id.) Your preliminary identification of the null event as a disk-read is even more likely if you see several null events that consistently point to the same database object.
Of course, the best solution to this puzzle is to fix the wait event diagnostics. Oracle Corporation has apparently fixed the problem in Oracle 184.108.40.206. Remember, however, that upgrading to 220.127.116.11 has nothing to do with actually solving the performance problem—it simply corrects the diagnostic routines so that the wait events are correctly named.
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It isn’t too late to register for the Northern California Oracle Users Group Summer Conference coming up on Thursday, August 21 in San Ramon, California. The Database Specialists team will lead a technical session on performance tuning using the wait event interface. (See http://dbspecialists.wpengine.com/presentations.html#wait_events2 for the white paper.)
When you’re at the conference, don’t forget to stop by our booth! You can learn more about NoCOUG and register at http://www.nocoug.org/next.html.