RE: many seconds waiting for I/O?
- From: "Dunbar, Norman" <norman.dunbar@xxxxxxxxxxxxxxxxxxxxxxxxx>
- To: "amonte" <ax.mount@xxxxxxxxx>
- Date: Fri, 27 Jul 2007 13:50:29 +0100
Hi Alex,
>> If it was sql*net messages why the event shows db file
>> sequential read?
A good question.
The 10g docs say that when the WAIT_TIME is non-zero that was the
sessions last wait time. I think I may have misinterpreted that to take
'last' to mean 'previous' - I do apologise.
Your WAIT_TIME was -1 so the wait is over and took less than one
hundredth of a second. The wait was indeed for 'db file sequential
read'. However, the SECONDS_IN_WAIT value is not how long the wait was
for because WAIT_TIME was -1 and that has a specific meaning of less
than 1 centi-second.
The more I read the 10g docs, the more confused I find myself getting!
For example it says that EVENT is the CURRENT wait event - what we are
waiting on now. But WAIT_TIME of -1 or -2 says the wait is over (so in
my book, EVENT should be null).
With WAIT_TIME = zero, then we are currently waiting and therefore EVENT
is what we are waiting on. SECONDS_IN_WAIT should be the time we have so
far waited.
With WAIT_TIME > zero then SECONDS_IN_WAIT is the time since the last
wait started, SECONDS_IN_WAIT - WAIT_TIME / 100 is the number of active
seconds since the last wait ended.
Clear as mud ??
So, what does it mean when SECONDS_IN_WAIT is high and WAIT_TIME is -1 -
which is what your problem appears to be?
Cheers,
Norman.
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