Re: Why Statistics doesn't match reponse time?

<poddar007_at_gmail.com> wrote in message
news:1126561319.704117.148040_at_g44g2000cwa.googlegroups.com...
> Hi jonathan
>
> Below is a quote from you
>
> "Buffer busy waits (of the change/change type)
> appear when one session pins exclusive and
> another wants to pin exclusive - the second
> session attaches to the 'waiters' pin-list and
> waits for the buffer to become available.
> But buffers are usually only pinned exclusive for very short periods. "
>
> Lets say a session pins a buffer in exclusive mode
> to make some changes.
>
> At the same time a session wants to read data
> from the buffer.
>
> Won't the second session (reader) would have to wait
> on buffer busy wait (120) till the first session has finished
> its change, so that it sees a consisten buffer ?
>
> thanks
> amit
>

Yes, you're right (though I'd have to check that it was p3=120 in that case, the only number I remember is 130 for waiting for other session to read from disk - which has become a separate wait event in 10g).

The first session would pin exclusive, the second would try to pin shared - but shared is not compatible with exclusive, so it would go on the waiters list and show a BBW.

-- 
Regards

Jonathan Lewis

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