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RE: many seconds waiting for I/O?

From: Dunbar, Norman <>
Date: Fri, 27 Jul 2007 13:50:29 +0100
Message-ID: <919FC80F27E0C6428106496EDF92A7524268BE@EXCCLUS05.PRODDS.NTNL>

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?


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Received on Fri Jul 27 2007 - 07:50:29 CDT

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